1869: Birth of ecology. Most people are unaware that the subdivision of biology called ecology is over a century old. Over the course of its development, ecology has emerged as one of the most significant and studied aspects of biology. Ecology refers to the overall interrelated system of nature and the interdependence of all living things.

The word ecology has been popularized more recently because of the many environmental concerns that have been raised since the 1970s. But as a word, ecology was coined in about 1869 by a German zoologist named Ernst Haeckel. A researcher in evolution and a strong supporter of Charles Darwin’s theories, Haeckel spent most of his career teaching at the University of Jena.

The study of ecology dates back to the ancient Greek philosophers. An associate of Aristotle named Theophrastus first described the relationships between organisms and their environment. Today the field of ecology has expanded beyond narrow biological studies to include environmental pollution, population growth, and food supplies.

Organisms considered harmful to humans or their interests are called pests. They include plants or animals that carry disease, cause disease, or destroy crops or structures. The definition of a pest is subjective. An ecologist would not necessarily consider a leaf-eating caterpillar on a corn plant a pest, but a farmer might. The term pest may refer to insects, viruses, and bacteria that carry or cause disease. It may also refer to organisms that destroy crops or man-made structures. Plants, such as weeds or fungi, and vertebrates, such as rats, mice, and birds, are sometimes called pests when they destroy crops or stored foods.

The elimination of pests or the inhibition of their reproduction, development, or migration is known as pest control. The control of pests has a great influence on the world economy. Even with current pest-control measures, agricultural pests are responsible for the annual destruction of millions of acres of crops worldwide. In South east Asia, rodents have been known to destroy as much as 50 percent of a rice crop before it is harvested. In the United States, over 500 million dollars are lost annually to insect and rodent infestation of stored foods and grains.

Some insects are considered pests because they are wood-eaters. They are a threat to wooden structures houses and other buildings, trees, and fences. Several species of ants, bees, and beetles can also damage wooden structures.

In the field of agriculture, pest control is used to protect farm crops and forests that are harvested for their wood. Pest control has also contributed to the management of many health-threatening diseases, including plague, encephalitis, yellow fever, malaria, and typhus.

Chemical Control

The most common method of pest control is the use of pesticides chemicals that either kill pests or inhibit their development. Pesticides are often classified according to the pest they are intended to control. For example, insecticides are used to control insects; herbicides to control plants; fungicides, fungi; rodenticides, rodents; avicides, birds; and bactericides to control bacteria. Pesticides also include chemosterilants and growth regulators, which are used to interfere with the normal reproduction or development of the pest.

Pyrethrum, old genus of composite family which botanists now place in genus Chrysanthemum; most garden varieties were derived from Chrysanthemum roseum, or Pyrethrum roseum, a handsome perennial with finely dissected leaves and white to crimson and lilac flowers; the flowers of Chrysanthemum cinerariaefolium, used in insecticides, had important part in U.S. troops’ fight against malaria-carrying mosquitoes in World War II.

Chemical control of pests probably began with poisonous plant compounds. In the 18th and 19th centuries, farmers ground up certain plants that were toxic to insects or rodents plants such as chrysanthemums or tobacco. The plant “soup” was then applied directly to either the crops or the pests. Chemists later discovered that they could extract the toxic compounds from these poisonous plants and apply the compounds as liquid sprays. Such chemicals as nicotine, petroleum, coal tar, creosote, turpentine, and pyrethrum (obtained from a type of chrysanthemum) were eventually extracted for use as sprays. Organic compounds such as these were eventually replaced by more effective inorganic chemicals, including arsenic, lime, sulphur, strychnine, and cyanide.

With the advent of synthetic organic compounds during World War II, a dramatic change occurred in pest control. The discovery of the insecticidal properties of the synthetic compounds DDT (dichlorodiphenyltrichloroethane) which was widely used against disease-spreading insects during the war and BHC (benzene hexachloride) made the notion of pest-free crops realistic. The development of another synthetic organic compound, the selective herbicide 2,4-D (2,4-dichlorophenoxyacetic acid), led to the development of other selective herbicides.

With the discovery of DDT, 2,4-D, and BHC, researchers began to develop other synthetic organic pesticides, especially growth regulators, chemosterilants, pyrethroids (compounds with insecticidal properties similar to those of pyrethrum), and organophosphate chemicals. This research expanded in order to develop other, non chemical, methods of pest control after the harmful persistence of pesticides in the environment was recognized. It was discovered in the 1950s that DDT and its related compounds are not easily broken down in the environment. DDT’s high stability leads to its accumulation in insects that constitute the diet of other animals. These high levels of DDT have toxic effects on animals, especially certain birds and fishes. Scientists also found that many species of insects rapidly develop populations that are resistant to the pesticide.

By the 1960s, the value of DDT as an insecticide had decreased, and in the 1970s severe restrictions were imposed on its use. In the United States, the Federal Environmental Pesticide Control Act of 1972 and the Federal Insecticide, Fungicide, and Rodenticide Act passed in 1972 required pesticide manufacturers to conduct scientific tests on the biological activity, defectiveness, persistence, and toxicity of any new pesticide before the chemical could be marketed. In the late 1980s, the average cost to develop and register a pesticide product was 10 million dollars. In the 1960s and 1970s, public objections were raised over the indiscriminate use of pesticides. The Environmental Protection Agency (EPA) was created in 1970 to ascertain past damage and possible future damage that could occur to the environment as the result of widespread pesticide use, and to set up programs to combat environmental problems.

An alternative concept of integrated pest management was adopted for many agricultural pests. This approach involves non-chemical pest-control methods, including crop exclusion, crop rotation, sanitation, and biological control. These methods augment other pest control programs designed to minimize pesticide usage.

Biological Control

The biological control of pests involves exposing them to predators or parasites. The use of predators and parasites is usually accompanied by a program in which pest-damaged fields are scouted and pest population estimates are made. Predators and parasites are then released by the millions to assure control of the target pest.

China (or People’s Republic of China), country in e. Asia; area 3,692,000 sq mi (9,561,000 sq km); cap. Beijing; pop. 1,165,888,000. Circa 1995.

Biological pest control was used by the ancient Chinese, who used predacious ants to control plant-eating insects. In 1776, predators were recommended for the control of bedbugs. The modern era of biological pest control began in 1888, when the vedalia beetle was imported from Australia to California to control the cottony-cushion scale insect. This biological control project saved the citrus-fruit industry.

Insect predators also have been used to control the bean beetle, tomato horn worms, and aphids. Another biological method is the use of bacteria against grubs, or insect larvae. For example, the bacterium Bacillus thuringiensis is used to control the caterpillar larvae of the gypsy moth, as well as the larvae of mosquitoes In the 1980s, mosquito-eating fish and nematodes that prey on such soil insects as corn root worms were introduced as biological-control agents.

Since the 18th century, the breeding of host plants for pest resistance also has been used to control pests. Wheat has been the object of the most extensive plant-resistance research. Effective wheat-breeding programs have led to the development of new wheat varieties that are resistant to rusts various parasitic fungi that infect the leaves and stems of the plant. Corn breeding has resulted in varieties resistant to other fungal diseases, including smut and leaf blight. The classic example of this plant-resistance approach to pest control was the control of phylloxera, insects that attacked the root stock of the European wine grape and almost completely ruined the European wine industry. The problem was solved by grafting the European plants onto the resistant American wine grape root stock.

The development of insect predators to control structural pests has met with little success. Nematodes have been used against termites in laboratories, but field tests have not been successful. Parasitic wasps used against various cockroach species have also been unsuccessful in the field.

Other Controls

Cultural control methods are used to alter the pest’s environment and thereby reduce access to breeding areas, food, and shelter. Cultural methods have been used to control the yellow-fever mosquito, which breeds in swamps and small pools of water. With the draining of swamps and the elimination of stagnant pools and other containers where water accumulates, the number of potential breeding places for the pest is reduced. Cultural control has also been used against structural pests, which depend on protected places such as cracks in side walks, roads, or buildings; garbage; and weeds for survival. Structural pests are often effectively deterred when openings to potential hiding places are sealed and debris and refuse are eliminated.

Crops are sometimes protected from harmful pests through diverse planting techniques. Crop rotation, for example, prevents the development of fungus and bacterium populations. Open-area planting relies on the wind to hinder flies and other insects that damage vegetable crops.

Physical or mechanical control methods are effective against some pests. Such controls include sticky barriers, heat killing (for storage pests), and flooding (for ground pests). Pressure-treated wood is protected against many wood-damaging fungi and insects. Traps are another mechanical method of pest control. Some traps are designed to either kill or capture rodents and other vertebrate pests. Netting and metal shields are used to keep birds from damaging fruit crops or from roosting on buildings. Electrical light traps attract insects and electrocute them. In some buildings, fans are installed above doors to prevent the entry of flying insects.

An area of pest-control research that has received much attention in recent years involves baiting traps with the pest’s own sex attractants, or pheromones. Pheromone traps have been used extensively against the fruit fly and gypsy moth. Pheromones are also being used to attract and trap pests that infest stored foods and grains.

Many countries use importation and quarantine regulations to control the importation of foreign plant or insect pests. Fruit is especially prone to insect infestation and disease. In the United States, the Animal and Plant Health Inspection Service monitors incoming products and materials and requires certain products to be treated prior to entry. Similar controls exist in other countries. Some regions have quarantine regulations to ensure that certain insect pests are not brought into the area. In the United States, individual states have their own inspection services. Some states even have border inspection stations to prevent unauthorized transport of plants across state lines.

Assisted by George W. Rambo.

DEFINITION:1 a) the branch of biology that deals with the relations between living organisms and their environment b) the complex of relations between a specific organism and its environment 2 Sociology the study of the relationship and adjustment of human groups to their geographical and social environments.

1869: Birth of ecology. Most people are unaware that the subdivision of biology called ecology is over a century old. Over the course of its development, ecology has emerged as one of the most significant and studied aspects of biology. Ecology refers to the overall interrelated system of nature and the interdependence of all living things.

The word ecology has been popularized more recently because of the many environmental concerns that have been raised since the 1970s. But as a word, ecology was coined in about 1869 by a German zoologist named Ernst Haeckel. A researcher in evolution and a strong supporter of Charles Darwins theories, Haeckel spent most of his career teaching at the University of Jena.

The study of ecology dates back to the ancient Greek philosophers. An associate of Aristotle named Theophrastus first described the relationships between organisms and their environment. Today the field of ecology has expanded beyond narrow biological studies to include environmental pollution, population growth, and food supplies.

The science that deals with the ways in which plants and animals depend upon one another and upon the physical settings in which they live is called ecology. Ecologists investigate the interactions of organisms in various kinds of environments. In this way they learn how nature establishes orderly patterns among a great variety of living things. The word ecology was coined in 1869. It comes from the Greek oikos, which means “household.” Economics is derived from the same word. However, economics deals with human “housekeeping,” while ecology concerns the “housekeeping” of nature.

Interdependence in Nature

Ecology emphasizes the dependence of every form of life on other living things and on the natural resources in its environment, such as air, soil, and water. Before there was a science of ecology, the great English biologist Charles Darwin noted this interdependence when he wrote: “It is interesting to contemplate a tangled bank, clothed with plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and so dependent upon each other in so complex a manner, have all been produced by laws acting around us.”

Ecology shows that people cannot regard nature as separate and detached something to look at on a visit to a forest preserve or a drive through the country. Any changes made in the environment affect all the organisms in it. When vehicles and factories hurl pollutants into the air, animals and plants as well as humans themselves are harmed. The water they foul with wastes and silt threatens remote streams and lakes. Even ocean fisheries may experience reduced catches because of pollution.

The Balance of Nature

Each kind of life is suited to the physical conditions of its habitat the type of soil, the amount of moisture and light, the quality of air, the annual variations in temperature. Each survives because it can hold its own with its neighbours However, the continued existence of the whole group, or life community, involves a shifting balance among its members, a “dynamic equilibrium.”

Natural balances are disrupted when crops are planted, since ordinarily the crops are not native to the areas in which they are grown. Such disturbances of natural balances make it necessary for man to impose artificial balances that will maintain or increase crop production. For the effective manipulation of these new equilibriums, information on nature’s checks and balances is absolutely essential, and often only a specialist is able to provide it. For example, if a farmer were told that he could increase the red clover in his pasture with the help of domestic cats, he might ridicule the suggestion. Yet the relationship between cats and red clover has been clearly established. Cats kill field mice, thus preventing them from destroying the nests and larvae of bumblebees. As a result, more bumblebees are available to pollinate clover blossoms. The more thoroughly the blossoms are pollinated, the more seed will be produced and the richer the clover crop will be. This cat-mouse-bee-clover relationship is typical of the cause-and-effect chains that ecologists study.

The Wide Scope of Ecology

Long before a separate science of ecology arose, men in all sorts of occupations were guided by what are now regarded as ecological considerations. The primitive hunter who knew that deer had to stop at a salt lick for salt was a practical ecologist. So too was the early fisherman who realized that gulls hovering over the water marked the position of a school of fish. In the absence of calendars, men used ecological facts to guide their seasonal endeavours They planted corn when oak leaves were the size of a squirrel’s ear. They regarded the noise of geese flying south as a warning to prepare for winter.

Natural history, the study of nature in general; forerunner of the sciences of biology and ecology.

Until about 1850, the scientific study of such phenomena was called natural history, and the student of the great outdoors was called a naturalist. Afterwards, natural history became subdivided into special fields, such as geology, zoology, and botany, and the naturalist moved indoors. There he performed laboratory work with the aid of scientific equipment.

While the scientists were at work in their laboratories, other men were continuing to cope with living things in their natural settings on timber lands, on range lands, on crop lands, in streams and seas. Although these men often needed help, many of their problems could not be solved in the laboratory.

The forester, for example, wanted to know why trees do not thrive on the prairie, the desert, and the mountaintop. The rancher wanted to know how to manage his pastures so that his cattle would flourish, and how such creatures as coyotes, hawks, rabbits, gophers, and grasshoppers would affect his efforts.

As for the farmer, almost every part of his work posed problems for which scientific answers were needed. The game manager came to realize that his duties entailed much more than the regulation of hunting. To preserve the animals for which he was responsible, he had to make sure they had the right kinds of food in all seasons, suitable places to live and raise their young, and appropriate cover.

The fisherman learned that most aquatic life fares poorly in muddy and polluted waters. He became interested in land management and waste disposal when he discovered that the silt he found so troublesome came from rural areas where timber, range land, and crop land were mishandled and that the waters he fished were polluted by urban wastes. The ocean fisherman wanted to know why fish were abundant in one place and scarce in another. He needed information on the breeding habits of his catches and of the tiny animals and plants upon which they fed.

These are all ecological problems. To solve them the ecologist must understand biology the science of living things including botany and zoology. He must also understand the sciences that deal with weather, climate, rocks, earth, soil, and water.

An ecologist is concerned with both the past and the future. The present and potential condition of a field, stream, or forest cannot be understood without knowing its earlier history. For example, great stretches of light-green aspen trees may grow in parts of the Rocky Mountains while nearby slopes are covered with dark-green fir and spruce trees. This indicates that a forest fire once destroyed stands of evergreens. Aspens are the first trees capable of growing on the fire-scarred land. After about 40 years spruce and fir seeds begin to germinate in the shade of the aspens. In the course of time the evergreens can be expected to regain their lost territory.

SOME PRINCIPLES OF ECOLOGY

Ecology is a relatively young science. Its laws are still being developed. Nevertheless, some of its principles have already won wide acceptance.

The Special Environmental Needs of Living Things

One of these principles can be stated as follows: life patterns reflect the patterns of the physical environment. In land communities vegetation patterns are influenced by climate and soil. Climate has a marked effect on the height of dominant native plants. For instance, the humid climate of the Eastern United States supports tall forest trees. Westward from Minnesota and Texas the climate changes from sub humid to semiarid. At first the land has squatty, scattered trees and tall grasses or thickets. As the climate becomes drier, tall-grass prairies dominate. Finally, on the dry plains at the eastern base of the Rockies, short-grass steppe appears.

Rocky Mountains (or Rockies), chain of ranges, along e. side of North American Cordilleras from Mexico to Alaska.

Climates and plant varieties change quickly at the various elevations of mountain range. At very high altitudes in the Rockies, alpine range lands exist above the timberline. Here, the climatic factor of cold outweighs that of moisture, and tundra vegetation similar to that of the Arctic regions is nurtured. West of the Rockies, however, in basins between other mountains, the desert scrub vegetation of arid climates prevails. Near the northern Pacific coast may be found lush rain forests typical of extremely humid temperature climates.

Though moisture and temperature determine the overall pattern of a region’s vegetation, unusual soil conditions may promote the growth of un-typical plant species. Thus, even in arid climates cat tails grow near ponds and forests rise along streams or from rocky outcrops where run off water collects in cracks.

Plants and animals flourish only when certain physical conditions are present. In the absence of such conditions, plants and animals cannot survive without artificial help. Domestic plants and animals ordinarily die out within a few generations without the continued protection of man. Of all the forms of life, man seems least bound by environmental limitations. He can create liveable conditions nearly everywhere on the planet by means of fire, shelters, clothing, and tools. Without these aids, man would be as restricted in his choice of habitat as are, for example, such species as the polar bear, the camel, and the beech tree. However, given his capacity to develop artificial environments, man is able to range not only over the entire Earth but also in the heights of outer space and the depths of the ocean bottom.

Communities of Plants and Animals

Community, in biology, a group of organisms living together in a particular environment.

Closely related to the life patterns principle is the principle of biotic communities. According to this principle, the plants and animals of a given area its biota tend to group themselves into loosely organized units known as communities. The community is the natural home of each member-species.

This means that certain types of plants and animals live together in readily identified communities. Pronghorn antelope are associated with dry steppe grasslands; moose inhabit northern spruce forests; and such trees as oak and hickory or beech and maple are found together in forests. By contrast, certain living things cat tail and cactus, for example never share the same natural environment.

Large communities in turn contain smaller ones, each with its own characteristic biota. Bison, coyotes, and jack rabbits are part of the grasslands community. Fox squirrels, wood pigeons, and black bears are part of the forest community. By means of computers, ecologists have simulated communities containing various plants and animals. In this way they have been able to determine optimum populations for each of the species in a community.

Competition in Communities

Competition is a characteristic of all communities. Plant roots in dry range lands compete for water. The trees of a rain forest compete for light. Crops compete for both of these as well as for nutrients. Competition is usually keen in areas where one type of community seems to overlap another. For example, a continuum between a shrub community and a marsh contains some aspects of both communities. Animals and plants trying to establish a foothold in such an overlap must cope with difficulties often non-existent in a stable community. Shrubs moving toward the marshy area must compete with other pioneer shrubs and reeds for light and nutrients.

Similarly, reeds attempting to invade the shrubby area must compete with shrubs and other reeds. This shows that competition may often be greatest among living things that have the same needs. For the same reason, competition may be extremely harsh within a species among wolves for meat or among cattle for grass, for example.

On the other hand, competition is sometimes modified through behavioural adjustments even cooperation among the members of a community. Shrubs are spaced widely on deserts. Birds nest in patterns that prevent overcrowding. Bees live together in a hive. Man can make similar adjustments, and unlike other species he can achieve cooperation by rational means. Yet human competition sometimes ends in wars, and wars frequently destroy the very things which the belligerents are striving to take away from one another.

Should it become necessary to control an undesirable species in a community, this can best be done by modifying the community. A rancher, for example, may discover that weedy annual plants are invading his native perennial pastures. His initial reaction might be to attack the weeds with chemical herbicides. This approach would be self-defeating since nature would provide the resultant bare soil with an unlimited supply of weed seed. To solve the problem ecologically, the rancher should modify the community by managing the degree and time of cattle grazing to permit normal growth of the native plant community, which would then crowd out the undesirable weeds.

Succession in Communities

A third major principle of ecology is that an orderly, predictable sequence of development takes place in any area. This sequence is called ecological succession. The successive changes produce increasingly mature communities from a barren or nearly barren start. Succession usually culminates in a climax, a fairly stable community in equilibrium with, and limited by, climate and soil.

At one time or another virtually all land surfaces have undergone basic climatic changes and been occupied by types of plants and animals which they may no longer be able to sustain. This, however, is not what is meant by ecological succession. It is known as biotic history, extends over the vast scale of geologic time, and is deduced from fossil remains. The future communities of an area cannot be predicted from its biotic history. Such prediction can be based only on a knowledge of ecological succession.

As soon as the first patches of soil are formed in barren areas, a series of events takes place that eventually terminates in the establishment of a climax community. This process is called primary succession. Because soil formation requires the slow weathering of rock, primary succession ordinarily spans hundreds of years. Once it begins, however, the sequence of events rarely alters. As soil formation proceeds, a succession of plants and animals appear. The last stage in this progression is the climax community.

Disclimax, an ecological community that occurs following a disturbance.

A disturbance at any point during primary succession or even at the climax can destroy the vegetation of a primary succession in whole or in part. The vegetation that follows a disturbance of this kind is called a disclimax. The disturbance can be caused by ploughing, logging, or overgrazing. When such a disturbance takes place, climate and soil are no longer the principal determinants of vegetation. The further natural growth of plants at the site of a disclimax, as contrasted with the raising of crops, is called secondary succession. This can be completed in a few years or, at most, in decades because soil has already been formed. After secondary succession restores a balance between eroded soil and vegetation, the further development of both again becomes dependent on primary succession. Wise landowners use secondary succession to restore overgrazed range lands, cut over timber lands, and abandoned crop lands They need only protect the land from further disturbances while secondary succession heals the scars of abuse.

Changes in the community during secondary succession are rapid, because every living thing contributes to its alteration. For instance, the weeds that grow on a vacant lot produce shade and increase the soil’s ability to absorb and store water. They also attract insects and birds and enrich the soil when they die and decay. The bare ground of the vacant lot is the best possible place for the pioneer sun-loving weeds to grow. Later the weeds are replaced by tree seedlings if the lot is in a forest climate, by native grasses if it is in a grasslands climate. Such changes occur until plants and animals that can make maximum use of the soil and climate are established.

The Ecosystem

A fourth key principle of ecology asserts that a community and its environment the living and the non-living constitute an ecological system, or ecosystem. Every natural community draws vital materials from its surroundings and transfers materials to it. Raw materials and decay products are exchanged continuously. Thus, in an undisturbed area basic resources are sustained, never exhausted.

Ecosystems exist on many kinds of lands, in lakes, in streams, and in oceans. They are found wherever soil, air, and water support communities. The combined ecosystems of the Earth constitute the biosphere.

Ecosystems generally contain many kinds of life. A cornfield, for example, contains more than just corn. Also present are smaller plant species, insects, earthworms, and a host of soil microbes. Each of these organisms fills a specific niche each performs an essential function in the ecosystem.

The inhabitants of an ecosystem are classified as producers, consumers, and decomposers. Green plants of any kind, whether stately oaks or tiny algae, are producers because they make their own food through photosynthesis. Animals, including man, feed on plants or on other animals and are therefore classed as consumers. Organisms that cause decay bacteria and fungi are decomposers.

Food chain, sequences in which organisms within an ecosystem feed on one another.

The sequences in which the organisms within an ecosystem feed on one another are called food chains. Usually organisms of higher biological rank feed on those of lower rank. Ecologists group the members of any food chain into a pyramid of numbers. At the base of such a pyramid are the green plants, which are the most numerous organisms in the chain. The next level might contain first-order consumers, such as the sheep that eat the green plants. At the peak of the pyramid might be second-order consumers, such as the herdsmen who feed on the sheep. When the producers and consumers of an ecosystem die, their bodies are broken down by the decomposers into nutrients used by new plants for growth. In this manner, the food chain is perpetuated.

The biosphere seems capable of sustaining life even in the absence of consumers. Without consumers, the rate of plant growth would eventually strike a balance with the rate of decay caused by the decomposers. Hence, even if all herbivores, or plant-eaters, were absent from the biosphere, plant growth could be expected to stabilize at certain levels.

Through plant growth and decay, water and carbon, nitrogen, and other elements are circulated in endless cycles. The driving force behind these cycles is the sun. Solar energy becomes converted into food through the photosynthesis of green plants and into heat through the respiration of plants and animals.

APPLICATIONS OF ECOLOGY

Ecologists are often employed to solve serious environmental problems. Early in this century, for example, southern Ohio was ravaged by a terrible flood. The inhabitants of the area, determined to prevent a repetition of the disaster, constructed large earthen dams across the valleys north of Dayton to contain future flood waters Since the slopes of these dams consisted of gravel with an admixture of clay, they washed away easily. It was necessary to stabilize the steep slopes quickly with plant cover. Knowing which plants would grow best in such places, an ecologist recommended the scattering of alfalfa and clover seed, followed by brome grass and Japanese honeysuckle. His recommendations were followed, and dam slopes were soon covered with a fine cohesive turf. Many of the hills on neighbouring farms lacked such cover and were quickly eroded.

In the Dust Bowl region of Texas, sandy soil in dry areas blew into great dunes after the land was ploughed for wheat. Bulldozing these dunes was thought too expensive. However, an ecologist recommended that certain plants be raised near the shifting dunes. The plants in front of the dunes caught and held the soil, while those behind them kept the rear from blowing deeper. In a short time, wind had levelled off the high dune tops and vegetation had anchored the soil.

Ecology and Wildlife Conservation

Measures for the preservation of ducks and other migratory wild fowl are examples of ecological work with animals. When these birds grew scarce, state and federal agencies sought ways to protect them and help them reproduce. At first, laws were recommended that forbade shooting the birds in the spring when they were flying north to nest. Every female killed in the spring could mean one less brood returning in the fall. Further studies showed that many of the birds’ breeding places were being destroyed when the land was drained for other uses. Some of these sites were not well-suited for the sustained growth of crops; others, where marshes and potholes once released stored water slowly, now contributed to downstream floods. Draining thus had a doubly harmful effect. Ecologists captured the endangered birds and put aluminium bands on their legs to trace their breeding places and movements. In this way it was discovered that the problem was international. As a result, the United States began to work in close cooperation with Canada and Mexico for the protection of migratory birds.

Ecologists also investigated the food habits of birds. They recognized that if proper food was unavailable, the birds would disappear even if hunting was regulated. Experts examined the stomach contents of thousands of birds from many different areas. This work led to the finding that bird food consists mainly of plant materials that thrive under natural conditions. To ensure the availability of these materials, man had to cease altering many natural communities and to stop polluting them with his wastes.

HOW DDT KILLED THE ROBINS. Dutch elm disease threatened to destroy most of the majestic elms that once flourished along residential streets. To eliminate the beetles that carry this fungus disease, many communities sprayed their elms with massive doses of DDT. The pesticide stuck to the leaves even after they fell in the autumn. Earthworms then fed on the leaves and accumulated DDT in their bodies. When spring came, robins returned to the communities to nest. They ate the earthworms and began to die in alarming numbers. Of the females that survived, some took in enough DDT to hamper the production or hatching of eggs. Robin populations were so seriously affected by DDT poisoning that the very survival of the songbird seemed in jeopardy. This experience was a vivid example of the far-ranging effects that flow from upsets in the delicate balances of nature.

Ironically, the DDT did little to prevent the spread of Dutch elm disease.

By the 1970s ecologists had accumulated considerable evidence demonstrating that the widely used pesticide DDT and its metabolites, principally DDE, altered the calcium metabolism of certain birds. The birds laid eggs with such thin shells that they were crushed during incubation. This discovery was one of many that led to the imposition of legal restraints on the use of some agricultural pesticides.

Ecologists know that the well-being of a biotic community may require the preservation of a key member-species. For example, the alligator performs a valuable service in the Florida Everglades by digging “‘gator holes.” These are ponds created by female alligators when they dig up grass and mud for their nests. During extremely dry spells, these holes often retain enough water to meet the needs of bobcats, raccoons and fish until the arrival of rainy weather.

Many birds use the holes for watering. Willow seeds take root along the edges, and fallen willow leaves later add substance to the soil. Thus, many forms of life are sustained by ‘gator holes. But poachers have been hunting the alligators almost to extinction for their valuable hides.

As a result, the number of ‘gator holes can be expected to dwindle, and various forms of Everglades wildlife may be deprived of these refuges. Such ecological findings strengthen the case for the protection of alligators.

Another ecological threat to the Everglades arose in the late 1960s, when plans were made to build a jet airport near the northern end of the national park. The airport would have wiped out part of a large swamp that furnishes the Everglades with much of its surface water. Ecologists and conservationists opposed the project, arguing that it would hamper the flow of surface water through the park and thus endanger the biota of the unique Everglades ecosystem.

Their arguments aroused public concern, and in 1970 plans for the airport were dropped.

An Ecological Mistake

Kaibab National Forest, forest in Arizona, adjoining Grand Canyon National Park; 1,780,475 acres (691,395 hectares); forest headquarters Williams, Ariz.

At times, seemingly practical conservation efforts turn out to be mistakes. Cougars, or mountain lions, and deer were once abundant in Grand Canyon National Park and Kaibab National Forest. Because the cougars preyed on the deer, hunters were allowed to shoot the cougars until only a few were left.

With their chief enemy gone, the deer of the area increased so rapidly that they consumed more forage than the Kaibab could produce. The deer stripped the forest of every leaf and twig they could reach and destroyed large areas of forage in the Grand Canyon National Park as well. The famished deer grew feeble, and many defective fawns were born. Finally, deer hunting in the Kaibab was permitted, in the hope that the size of the deer herd would drop until the range could accommodate it. In addition, the few surviving cougars were protected to allow them to multiply. They then resumed their ecological niche of keeping the herd size down and of killing those deer not vigorous enough to be good breeding stock.

The Ecological Control of Pests

Many of the insects and other pests that have plagued North America originated elsewhere. There these pests were held in check by natural enemies, and the plants and animals they infested had developed a measure of tolerance toward them. However, when they were placed in an environment free of these restraints, the pests often multiplied uncontrollably.

At first, farmers fought the pests with toxic sprays and other powerful chemicals. However, these methods were expensive, sometimes proved unsuccessful, and were often dangerous. After decades of use, some pesticides were banned. In certain instances, pesticide use gave way to an ecological approach.

Research showed that severe damage from certain pests the Mexican beetle and the European corn borer, for example is confined to crops grown on particular types of soil or under certain conditions of moisture. Changes in land use helped control some pests. Others were controlled biologically by importing parasites or predators from their native lands. This important form of pest control proved successful in limiting damage by scale insects.

By destroying birds and other animals, as well as their breeding places, people lose valuable allies in their constant war with insects. Once, when the sportsmen of Ohio supported a proposal to permit quail hunting, the farmers of the state objected. They knew that a single quail killed enough insects to make it worth at least as much to them as a dozen chickens.

In some 3,000 locally organized Resource Conservation Districts ecological principles are being used to guide land use and community maintenance practices. These districts encompass the federal lands of the United States and more than 95 percent of its privately owned farmlands.

GOALS OF ECOLOGY

Throughout the world man-made communities have been replacing the communities of nature. However, the principles that govern the life of natural communities must be observed if these man-made communities are to thrive. People must think less about conquering nature and more about learning to work with nature.

In addition, each person must realize his interdependence with the rest of nature, including his fellow human beings. To safeguard life on Earth, people must learn to control and adjust the balances in nature that are altered by their activities.

Maintenance of the Environment

Climate cannot be changed except sporadically by cloud seeding, inadvertently by pollution, and on a small scale by making windbreaks or greenhouses. However, human activities can be successfully adapted to the prevailing climatic patterns. Plants and animals, for example, should be raised in the climates best suited to them, and particular attention should be paid to the cold and dry years rather than to average years or exceptionally productive years. In the United States the serious dust storms of the 1930s occurred because land that was ploughed in wet years to grow wheat blew away in dry years. Much of that land should have been kept as range land

Soil is a measure of an environment’s capacity to support life. It forms very slowly but can be lost quickly as much as an inch in a rainstorm. Wise land use ensures its retention and improvement.

For agricultural purposes, land is used principally as timber land, range land, or crop land Timber land and range land are natural communities. Crop land is formed when what was originally timber land or range land is cultivated. To ensure the best possible use of land, it is classified according to its ability to sustain the production of timber, pasture, or crops.

Water, like soil, is a measure of the abundance of life. Usable water depends on the amount and retention of rainfall. An excessive run-off of rainwater, however, may result from human activities for example, the building of roads and drainage ditches; the construction of extensive parking areas and shopping centres; the unwise harvesting of timber; year-round grazing of ranges; and the cultivation of easily eroded lands. Excessive run-off may cause floods. It may also lead to drought, which can occur when too little water is stored underground. Moreover, run-off strips soil from the land. This is deposited in reservoirs, ship channels, and other bodies of water. These silt-laden bodies must then be either dredged or abandoned. Water movements in and out of the soil must be controlled in such a way as to minimize damage and maximize benefits.

The Conservation of Natural Communities

Community, in biology, a group of organisms living together in a particular environment.

The communities of plants and animals established by humans usually consist of only a few varieties, often managed in a way that harms the environment. By contrast, natural communities usually enhance the environment and still yield many products and sources of pleasure to people.

Land once cultivated but now lying idle should be restored to the natural communities that formerly occupied it. In addition, people should use the findings of ecology to improve their artificial communities such as fields, gardens, orchards, and pastures. For example, few man-made agents for the control of pests can outperform the wide variety of insect-eating birds.

The Curtailment of Waste

Modern machines and weapons and the harmful wastes of technology can be used to destroy the environment. At the same time, the wise use of machinery can also enable humans to conserve their surroundings. Just as negotiation rather than warfare can be employed to resolve international disputes, no doubt the means can be devised to curtail the destructive wastes of factories and vehicles. True, ever-growing demands for goods and services, nurtured by increasing human populations and rising expectations, are placing more and more pressure on the environment. An understanding of the causes and consequences of environmental deterioration, however, may bring about a change in the goals that people pursue and the means they use to achieve these goals.

Increases in human material possessions have been accompanied by a potentially dangerous worsening of the natural environment. A central function of ecology is to study human interactions with the natural environment in order to modify them favourably.

Assisted by E.J. Dyksterhuis, Professor of Range Ecology, Texas A & M University.

BIBLIOGRAPHY FOR ECOLOGY

Books for Children

Jaspersohn, William. How the Forest Grew (Greenwillow, 1980).

Pringle, Laurence. City and Suburb: Exploring an Ecosystem (Macmillan, 1975).

Sabin, Francene. Ecosystems and Food Chains (Troll, 1985).

Selsam, M.E. How Animals Live Together, rev. ed. (Morrow, 1979).

Books for Young Adults

Billington, E.T. Understanding Ecology, rev. ed. (Warne, 1971).

Pringle, Laurence. Lives at Stake: The Science and Politics of Environmental Health (Macmillan, 1980).

Sharpe, G.W. Interpreting the Environment, 2nd ed. (Wiley, 1982).

Sharpe, G.W. and others. Introduction to Forestry, 4th ed. (McGraw, 1976).

The reasonable use of the Earth’s natural resources water, soil, wildlife, forests, and minerals is a major goal of conservation. Conservation is the preservation and maintenance of the environment to meet human needs for production while insuring that proper consideration is also given to aesthetics and recreation. An effective conservation program results in a continuous production and supply of native plants and animals, and the continued availability of critical mineral resources. Timber, fuels, ores, and other resources are being depleted at such a rapid rate that the need to conserve them has become crucial. The prevention of environmental pollution from industrial, agricultural, urban, and domestic sources, including toxic chemicals, radioactive wastes, and elevated water temperatures, is another concern of conservation. People concerned with conservation seek to prevent the waste of natural resources, to maintain a high-quality environment, and to preserve the natural heritage for future generations.

1869: Birth of ecology. Most people are unaware that the subdivision of biology called ecology is over a century old. Over the course of its development, ecology has emerged as one of the most significant and studied aspects of biology. Ecology refers to the overall interrelated system of nature and the interdependence of all living things.

The word ecology has been popularized more recently because of the many environmental concerns that have been raised since the 1970s. But as a word, ecology was coined in about 1869 by a German zoologist named Ernst Haeckel. A researcher in evolution and a strong supporter of Charles Darwin’s theories, Haeckel spent most of his career teaching at the University of Jena.

The study of ecology dates back to the ancient Greek philosophers. An associate of Aristotle named Theophrastus first described the relationships between organisms and their environment. Today the field of ecology has expanded beyond narrow biological studies to include environmental pollution, population growth, and food supplies.

2300 BC: Invention of paper In ancient Egypt paper was made from the papyrus plant. The stalk was split, sliced, pressed and dried into thin sheets. In China, a government servant named Ts’ai Lun is credited with inventing paper in AD 105. He made the paper from mulberry fibres, hemp waste, rags, fish nets, and other materials. It took many centuries for this invention to travel west: it reached Samarkand, in Central Asia, by 751 and Baghdad by 793. Finally, through Arab contacts, this technology arrived in Europe in about the 12th century. Three hundred years later the invention of printing with moveable type spurred the demand for paper in Europe. Even so, processes for making it were not technologically advanced, and shortages persisted for several hundred years. The use of wood pulp in the early 19th century greatly increased the paper supply. In the 20th century, concern over deforestation led to the growth of recycling processes for paper.

 Soot, car fumes, and acid rain pollute the air.

The world’s rain forests are being destroyed.

Toxic waste and garbage contaminate the water.

Pesticides and chemicals poison our food.

Strip mining ravages the land.

Gas and oil are wasted.

Humans have been slowly destroying the world’s resources for years.

The goal of conservation is to make the environment clean and healthy while continuing to use the Earth’s resources. This goal is gaining popularity throughout the world as all nations begin to see the results of abusing the environment.

Everyone must think seriously about the environment. Humans cannot live happy, healthy lives in an unhealthy world.

Renewable Resources can be maintained with careful planning. Examples include:

wild animals

forests

soil and water

grasslands

Non-renewable Resources will eventually be used. Examples are:

oil, coal, and gas

gold and silver

uranium

iron

Natural resources are sometimes classified as renewable or non-renewable Forests, grasslands, wildlife, and soil are examples of renewable resources. They can be regenerated, and prudent management can maintain them at steady levels. Such resources as coal, petroleum, and iron ore are non-renewable Consumption, wasteful or not, of their limited supply speeds the rate at which they are depleted.

Every creature, large or small, plays a part in the balance of nature.

Balance of nature means the way in which everything in nature depends upon other things in nature in order to live. All of nature works well together, with one creature or plant or mineral supporting others. Sometimes it appears that the elements of nature are not working well together, for example when a volcano erupts or when lightning starts enormous forest fires. However, both of these events that may seem like total disasters are extremely helpful in that they make it possible for new habitats to be created.

In many cases, people have upset this balance of nature. The Earth’s environment can handle some of the bad things done to it, but with so many people living on the Earth, there’s no such thing as “a little bit” of damage. All people on Earth need a healthy, balanced environment.

Natural resources are a vital part of sustaining human life, and conservation measures are designed to control, manage, and preserve them so that they can be used and appreciated to the fullest. Freshwater habitats must be kept clean for drinking and for recreational activities. Soils must be kept fertile, without the accumulation of toxic chemicals from pesticides or herbicides, to provide fruits and vegetables. Forests must be managed in a manner that can provide not only lumber and pulpwood for paper products but also homes for native wildlife. The use of oil, coal, and minerals important for an industrial society must be carefully monitored to be certain that the supply does not dwindle too rapidly. The proper conservation of these natural resources is of key concern in maintaining the balance of nature in a world with a large human population.

The Abuse of Natural Resources

When the first European settlers arrived in North America, they found a continent rich in natural resources. Much of the land was covered with forests where wild animals abounded. Great herds of bison roamed the grasslands. The soil was deep and fertile. Clean lakes and streams, unpolluted with silt and chemical wastes, held a wealth of fish.

In the struggle to obtain food, clothing, and shelter the settlers cut down and burned most of the Eastern forests. As they moved westward, they ploughed up the grasslands to plant corn and wheat. Their growing cities dumped sewage and waste materials from factories into the lakes and streams.

The roots of hundreds of thousands of ground-covering plants and grasses form a sponge-like net that holds the topsoil in place and soaks up rainwater.

If this plant cover is removed:

There is no net to hold the soil down, and nothing for rain to soak into.

The good soil needed for farming and the water needed to fill underground reservoirs wash away into streams and rivers.

Flooding occurs because the rivers and streams can’t hold all of the water and soil that is washing away.

Flooding is a major problem in areas of North America where rain tends to fall quickly in heavy thunderstorms. In Europe rains usually fall slowly and gently enough not to wash away bare topsoil.

The settlers who first came to North America didn’t know that the heavy rains of America would cause so much damage to bare soil. They also had no idea that the methods they used to plough and plant crops were causing soil problems to worsen.

Much of the spring and summer rain in the United States falls in torrential thunderstorms, especially in the vast Missouri, Mississippi, and Ohio river basins. The farmers who settled the country were mainly Europeans who had been used to gentle rains. The methods of tilling and planting which they brought with them were not suited to the new climate. The land’s capacity for water storage was diminished by the loss of the grasses that hold soil in place and prevent the escape of rainwater. With the blotter like plant cover gone, many rivers flooded when the winter snows melted. During natural drought periods, wells ran dry and crops died in the fields. Dust storms blew the topsoil away. Birds and animals that once thrived in the forests and on the prairies became scarce. Some kinds vanished forever. Fish died in the unclean waters.

The Conservation of Natural Resources

The Earth’s environment will continue to become less healthy unless all nations work together to improve it. To protect our world, everyone must understand the need for conservation.

People who worry about the environment have grouped together into organizations that fight for conservation, such as:

the Sierra Club

Greenpeace

the Nature Conservancy

the World Wildlife Fund

Many of these groups have succeeded in getting laws passed to protect land, wildlife, and other natural resources. Once laws have been passed, anyone who disobeys them can be punished.

The abuses of the past and even the present have emphasized the need for the wise use of natural resources. Conservation groups have promoted corrective legislation and instituted legal proceedings against violators. People have been made increasingly aware that their continued existence depends on these efforts to stop environmental deterioration.

Individuals have no right to destroy nature’s wealth for profit. The logging company that cuts down too many trees without replanting for the future; the industrial plant that fouls a river or pollutes the air with its wastes; the farmer who neglects his own farm and so damages his neighbour’s land are injuring their whole community. The camper whose carelessness starts a forest fire; the automobile driver who wastes gasoline; the picnickers who tear up armfuls of wild flowers or litter the landscape with their garbage; the hunter who kills more than the legal limit all are abusing natural resources. Conservation is everyone’s responsibility. It is a uniquely human problem. Stringent laws to stop the waste and destruction of natural resources must be supported and effectively enforced.

RESULTS OF LACK OF CONSERVATION

1. Rampant streams destroy land and fail to recharge underground water sources.

2. Bad forestry leaves timber fire-prone and causes soil erosion and flooding.

3. Poor farming methods drain soil fertility and hasten erosion by wind and water.

4. Sprawling, monotonous suburbs blight good land and foster obsolescence.

5. Rural industrial parks create pollution that can affect downstream communities.

6. Abandoned mining operations poison streams and permanently scar the landscape.

7. Haphazard placement of industry leads to the pollution of water and air in cities.

8. Failure to treat garbage and sewage adequately contaminates the surroundings.

9. Bad industrial zoning downgrades nearby property and produces urban eyesores.

10. Polluted rivers cannot sustain fish life and need costly purification for drinking.

11. Poorly managed traffic facilities snarl urban travel and aggravate air pollution.

12. Densely grouped high-rise apartment buildings wall out air and sunlight.

Conservation can help maintain the natural beauty of a community. When land is mistreated, the countryside can become unattractive. Vacant lots covered with trash, bare roadsides, and garbage-laden streams are ugly. Conservation also helps preserve areas suitable for recreation. As cities grow crowded, natural areas are needed for people enjoying leisure time. People need city parks, county forest preserves, and national parks; grass and trees bordering roads and highways; and sparkling streams.

The Prairie Dog Coterie – A Complex Social Group

The prairie dog is a rodent that maintains an elaborate social organization. Bond formation among prairie dogs depends on the exchange of auditory, visual, and chemical stimuli. The coterie the social unit of the prairie dog is maintained in a network of burrows occupying a fairly restricted area.

Prairie dog pups are altricial at birth that is, they are so undeveloped that they need adult aid for survival. When the pup is born, its mother is attracted to the helpless young organism. She licks the pup as it emerges from the birth canal, thus replenishing the salts she lost before and during birth. While licking the pup, she breaks the sac in which it developed as an embryo and thus stimulates its breathing response. The pup, still wet from birth, is attracted to the warmth of the mother’s body. Moments after birth, the mother and her offspring are exchanging highly attractive stimuli, quickly forming a social bond. As the pup nurses, it relieves the pressure in the mother’s milk gland. Again, the exchange of stimulation strengthens the bond between the mother and her offspring, thus helping to ensure the infant’s survival.

As the pup matures, other stimuli become attractive. When it is able to see and hear, the pup begins to recognize the relationship between stimuli that occur at the same time. Soon it leaves its burrow and encounters other adults that it stimulates. From birth, the prairie dog is constantly nuzzled and licked by its mother. When it emerges from its burrow, it is handled similarly by other prairie dogs.

Grazing land, non farm area where animals feed on grass or other plants.

These behavioural patterns maintain prairie dogs in a well-organized life space. There, the family unit reproduces, finds shelter, and feeds. Being grazers, prairie dogs check the growth of tall grasses that would prevent them from easily spotting predators. At the same time, their grazing habits encourage the dominance of fast-growing plants. Thus, the social organization of prairie dogs influences the ecological balances in their environment. Limited grazing space soon forces maturing prairie dogs to seek new areas. When they enter the burrows of another coterie their odour marks them as strangers, and they are rejected. Pairs of rebuffed animals band together to form new coteries.

The Chimpanzee Family

The chimpanzee is one of the great apes. It lives in a family unit even more complex than that of the prairie dog. The chimpanzee family moves as a group through familiar feeding and resting areas. It has also evolved effective ways of defending itself against predators or from belligerent chimpanzees attempting to mate with the family’s females.

When a chimpanzee has been attacked or has spotted a predator, it lets out an intense cry that raises the level of excitement of the other members of the family. They scream at the predator, throw rocks and other objects, and scamper off. As they flee, the females and the youngest chimpanzees are surrounded by the juveniles and the young males. The largest males guard the group. Thus, the action of a single chimpanzee serves as a signal that affects the behaviour of the rest of the family.

Animal Communication

Communication in the animal world takes many forms. These include chemical, visual, and audible signals. Attacked insects secrete a pheromone that so excites their con-specifics that they either attack or escape from the predator. Flocks of birds behave similarly, except that sounds rather than chemicals trigger the response. Vocalization also evokes social responses in the porpoise, an aquatic mammal. Porpoises communicate by means of whistles and other sounds. When a porpoise is born, females may be attracted by the mother’s whistles. They swim to the baby and nuzzle it. The mother does not attack other females at this time. Possibly, this experience with many adult porpoises in the earliest days of infancy helps form the tight social bond of porpoises.

Reciprocal stimulation affects the behaviour of any animal, whether briefly or for a long time. Each organism is the source of environmental changes that affect other organisms. For example, after an amoeba ingests a food particle, it excretes a metabolic by-product that changes the chemical characteristics of the environment. If another amoeba is nearby, it tends to approach the first, though it will not do so if the chemical concentration is too intense. A sexually mature male cricket stridulates rubs its legs together and produces a sound whether or not another cricket stimulates it. However, it is more likely to stridulate when it hears another cricket.

When one animal can prompt an anticipated response in another, it displays a more advanced type of communication. For example, in an experiment a chimpanzee was trained to obtain a banana by pulling on a rope attached to a weight. Then the experimenter increased the weight so that one chimpanzee could not raise it but two could. If the second chimpanzee had already been trained to pull the rope, the first was able to stimulate it to do so by gesture, vocalization, and shoving. The two would then pull together and get the banana. In this case, the consequence of the second chimpanzee’s behaviour was in some way anticipated by the first.

The directed activity of one animal toward another for the solution of a problem or the attainment of a planned goal is evident only in advanced species. Furthermore, man is the only species capable of transmitting ideas through a complex system of speech and writing.

The study of the evolution of language has given rise to a science called semiotics. This science attempts to understand the similarities and the differences among the many forms of communication.

Heredity and Behaviour

The evolutionary principle of selective adaptation holds that a species survives when it is able to adapt to environmental changes and when it is able to transmit to its offspring the genetic information that makes such adaptations possible. But how do genetic processes contribute to the development of behavioural patterns? Which behavioural patterns are hereditary? Which must be learned by each new generation?

In an effort to answer such questions, behavioural scientists have designed a number of experiments. In one type of experiment, closely related species with distinctly different behaviour patterns are hybridized. For example, two species of parakeets that practically share a natural habitat but do not interbreed were crossed in the laboratory. The parakeets of one species ordinarily tuck nesting material under their tail feathers. The others carry it in their beaks. The hybrid female offspring made inadequate tucking motions with the nesting material, and the twigs fell out from their feathers. However, all the hybrids carried the nesting material successfully in their beaks. Scientists felt that since all the hybrids performed some part of the tucking behaviour, it was probably the earlier form of behaviour in the evolution of these species.

The relationship between heredity and behaviour has fuelled an old but continuing controversy in the behavioural sciences. Some scientists believe that genetic processes underlie every kind of behaviour, while others think that the environment can modify genetically influenced behaviour In one type of experiment testing these views, animals with different genetic backgrounds are reared in the same environment. In another type, animals with the same genetic backgrounds are raised in different environments.

Chaffinch, European bird of the finch family, sought as a cage bird because of its beauty of voice and its ability in learning to sing tunes.

Cross-fostering is used to rear species with different genetic backgrounds in the same environment that is, the young of one species are raised by a female of another species. In one cross-fostering study, a female great tit reared a baby chaffinch with her own babies. Great tits and chaffinches are closely related birds that feed in different ways. The great tit holds food under its feet; the chaffinch does not. A chaffinch hatched by a great tit did not use its feet during feeding, while its nest mates did. Its feeding behaviour remained typical for its species, although it had no opportunity to observe other chaffinches.

However, when a great tit was reared in isolation, though it too demonstrated species-typical behaviour by holding its food down, it did so very clumsily. Only after repeated tries did its performance improve. This experiment showed that experience may be important even in genetically determined behavioural patterns.

Manipulation of the physical environment was used to study the subspecies of deer mice. One subspecies lives in the forest, is a climbing animal, and has a longer tail and larger ears than the other, a prairie subspecies that lives in grassy fields. The two subspecies were reared in the same laboratory and then released in a room containing artificial grass and wooden posts with flat tops. Although neither subspecies had experienced its species-typical environment, the forest deer mice organized their life space around the “trees,” and the prairie deer mice settled under the “grass.” However, when prairie deer mice were bred in a laboratory for more than a dozen generations, they no longer showed a preference for the field. The environment eventually so altered the genetic processes of these experimental animals as to change their species-typical behaviour

Meadowlark, bird of the genus Sturnella, family Icteridae; sharp-billed, 8 to 11 in. (20 to 28 cm) long; two North American species streaked brown above, with yellow breast crossed by black V; western meadowlark (S. neglecta) known for intricate fluting call.

Bird-song patterns are species-specific and have, therefore, been regarded as genetically determined. Studies of the development of species-typical song patterns have helped to clarify the relative roles of heredity and experience in the development of such patterns. For example, if a meadowlark is exposed to another bird’s song while it is learning to sing it will learn the other bird’s song; however, if the meadowlark is exposed to the songs of other meadowlarks along with those of another species, it will learn only its own species-typical song. The bird instinctively chooses its species-typical song when it is in a situation in which there is a choice.

The response patterns of birds are so varied that the contributions made by genetic processes and by the auditory and other experiences of a bird during singing are hard to separate. It may be that in the course of its development a bird produces certain sounds that are a function of its peculiar body make-up These sounds may be the fundamental vocalization of the bird’s species. Additional experience by the bird with hearing and producing its own song, as well as hearing those of other birds in a social setting, may yield the “dialect,” or song pattern, associated with the species. However, genes do not carry this pattern as such. Rather, they carry the code for the biochemical processes that develop certain body systems that, aided by experience, will affect the animal’s behaviour in its typical environment.

Assisted by Ethel Tobach, Curator, Department of Mammalogy, American Museum of Natural History, New York City.

BIBLIOGRAPHY FOR ANIMAL BEHAVIOUR

Black, Hallie. Animal Cooperation: A Look at Sociobiology (Morrow, 1981).

Caras, Roger. The Private Lives of Animals (McGraw, 1987).

Fraser, A.F. Farm Animal Behaviour, 2nd ed. (Saunders, 1983).

Freedman, Russell and Morriss, J.E. The Brains of Animals and Man (Holiday, 1972).

Lydecker, Beatrice. What the Animals Tell Me (Harper, 1982).

McFarland, David, ed. The Oxford Companion to Animal Behaviour (Oxford, 1981).

National Geographic Society. How Animals Behave (National Geographic, 1984).

Pringle, L.P. Animals at Play (Harcourt, 1985).

Pringle, L.P. The Secret World of Animals (National Geographic, 1986).

Waller, E.J. Why Animals Behave the Way They Do (Scribner, 1981).

 

Industrial Pollution

Efforts to improve the standard of living for humans through the control of nature and the development of new products have also resulted in the pollution, or contamination, of the environment. Much of the world’s air, water, and land is now partially poisoned by chemical wastes. Some places have become uninhabitable. This pollution exposes people all around the globe to new risks from disease. Many species of plants and animals have become endangered or are now extinct. As a result of these developments, governments have passed laws to limit or reverse the threat of environmental pollution.

All living things exert some pressure on the environment. Predatory animals, for example, reduce the population of their prey, and animal herds may trample vast stretches of prairie or tundra. The weather could be said to cause pollution when a hurricane deposits tons of silt from flooded rivers into an estuary or bay. These are temporary dislocations that nature balances and accommodates to. Modern economic development, however, sometimes disrupts nature’s delicate balance. The extent of environmental pollution caused by humans is already so great that some scientists question whether the Earth can continue to support life unless immediate corrective action is taken.

Ecology and Environmental Deterioration

The branch of science that deals with how living things, including humans, are related to their surroundings is called ecology. The Earth supports some 5 million species of plants, animals, and micro-organisms These interact and influence their surroundings, forming a vast network of interrelated environmental systems called ecosystems. The Arctic tundra is an ecosystem and so is a Brazilian rain forest. The islands of Hawaii are a relatively isolated ecosystem. If left undisturbed, natural environmental systems tend to achieve balance or stability among the various species of plants and animals. Complex ecosystems are able to compensate for changes caused by weather or intrusions from migrating animals and are therefore usually said to be more stable than simple ecosystems. A field of corn has only one dominant species, the corn plant, and is a very simple ecosystem. It is easily destroyed by drought, insects, disease, or overuse. A forest may remain relatively unchanged by weather that would destroy a nearby field of corn, because the forest is characterized by greater diversity of plants and animals. Its complexity gives it stability.

Every environmental system has a carrying capacity for an optimum, or most desirable, population of any particular species within it. Sudden changes in the relative population of a particular species can begin a kind of chain reaction among other elements of the ecosystem. For example, eliminating a species of insect by using massive quantities of a chemical pesticide also may eliminate a bird species that depends upon the insect as a source of food.

Such human activities have caused the extinction of a number of plant and animal species. For example, over hunting caused the extinction of the passenger pigeon. The last known survivor of the species died at the Cincinnati Zoo in 1914. Less than a century earlier, the passenger pigeon population had totalled at least 3 billion. Excessive hunting or infringement upon natural habitats is endangering many other species. The great whales and the California condor are among the endangered.

Population Growth and Environmental Abuse

The reduction of the Earth’s resources has been closely linked to the rise in human population. For many thousands of years people lived in relative harmony with their surroundings. Population sizes were small, and life-supporting tools were simple. Most of the energy needed for work was provided by the worker and animals. Since about 1650, however, the human population has increased dramatically. The problems of overcrowding multiply as an ever-increasing number of people are added to the world’s population each year.

The rate of growth of the world’s population has finally begun to slow, after reaching an all-time high of about 2 percent in 1970. In 1987 there were 5 billion people on the planet. The United Nations predicts the population growth rate will decline to 1.5 percent by the year 2000. Even so, there will be 6.1 billion people living on Earth at the beginning of the 21st century twice the number of people living on Earth in 1960.

The booming human population is concentrated more and more in large urban areas. Many cities now have millions of inhabitants. In less developed countries of Asia, Africa, and Latin America, many of these cities are overpopulated because of an influx of people who have left rural homes in search of food, shelter, and employment. Some farmers have been forced off their land by drought and famine.

Environmental pollution has existed since people began to congregate in towns and cities. Ancient Athenians removed their refuse to dumps outside the main part of the city. The Romans dug trenches outside the city to hold garbage and wastes (including human corpses), a practice which may have contributed to outbreaks of viral diseases.

The ancient Romans may have been among the first people to experience the effects of toxic pollution in the form of lead poisoning. Like many other minerals and metals, lead can enter the body with food or drink or may be inhaled with particles of dust. The accumulation of lead in the blood and other tissues can cause severe illness or, in large quantities, death. The Romans used lead to line the inside of bowls and pitchers. It was also used for plates, cups, and spoons. In some areas, it was used in plumbing systems. Some historians believe that the long-term exposure to lead was a major health risk for the Romans.

The adverse effects of pollution became more noticeable as cities grew during the Middle Ages. In Europe, medieval cities passed ordinances against throwing garbage into the streets and canals, but those laws were largely ignored. In 16th-century England, efforts were made to curb the use of coal in order to reduce the amount of smoke in the air again with little effect.

In the 19th century, the Industrial Revolution placed greater pressures on the environment, and pollution changed and increased dramatically. Although industrial development improved the standard of living, there was a great environmental cost.

Air Pollution

Factories and transportation depend on huge amounts of fuel billions of tons of coal and oil are consumed around the world every year. When these fuels burn they introduce smoke and other, less visible, by-products into the atmosphere. Although wind and rain occasionally wash away the smoke given off by power plants and auto mobiles, the cumulative effect of air pollution poses a grave threat to humans and the environment.

Smog, combination of fog and smoke; common in industrial areas.

In many places smoke from factories and cars combines with naturally occurring fog to form smog. For centuries, London, England, has been subjected to the danger of smog, long recognized as a potential cause of death, especially for elderly persons and those with severe respiratory ailments. Air pollution in London originally resulted from large-scale use of heating fuels.

A widespread awareness of air pollution dates from about 1950. It was initially associated with the Los Angeles area. The Los Angeles Basin is ringed for the most part by high mountains. As air sinks from these mountains it is heated until it accumulates as a warm layer that rises above the cooler air from the Pacific Ocean. This results in a temperature inversion, with the heavier cool air confined to the surface. Pollutants also become trapped at surface levels. Because of air-circulation patterns in the Los Angeles Basin, polluted air merely moves from one part of the basin to another part.

Scientists believe that all cities with populations exceeding 50,000 have some degree of air pollution. Burning garbage in open dumps causes air pollution. Other sources include emissions of sulphur dioxide and other noxious gases by electric power plants that burn high-sulphur coal or oil. Industrial boilers at factories also send large quantities of smoke into the air. The process of making steel and plastic generates large amounts of smoke containing metal dust or microscopic particles of complex and sometimes even deadly chemicals.

The single major cause of air pollution is the internal-combustion engine of auto mobiles Gasoline is never completely burned in the engine of a car, just as coal is never completely burned in the furnace of a steel mill. Once they are released into the air, the products of incomplete combustion particulate matter (soot, ash, and other solids), unburned hydrocarbons, carbon monoxide, sulphur dioxide, various nitrogen oxides, ozone, and lead undergo a series of chemical reactions in the presence of sunlight. The result is the dense haze characteristic of smog. Smog may appear brownish in colour when it contains high concentrations of nitrogen dioxide, or it may look blue-grey when it contains large amounts of ozone. In either case, prolonged exposure will damage lung tissue.

The costs of air pollution are enormous. The American Lung Association sites sulphur-dioxide exposure as the third leading cause of lung disease after active and passive smoking. Contaminants in the air also have been implicated in the rising incidence of asthma, bronchitis, and emphysema, a serious and debilitating disease of the lung’s air sac.

pH, quantitative measure of the acidity or basicity of liquid solutions.

In the mid-1970s, people became aware of the phenomenon called acid rain. When sulphur dioxide emissions from electric power plants combine with particles of water in the atmosphere, they fall to ground as acid rain or snow. The acidity or basicity of liquids, including rainfall and snow, is measured by a special scale, called the pH scale. Developed in 1909 by the Danish biochemist S.P.L. Sorensen, the pH scale is used to describe the concentration of electrically charged hydrogen atoms in a water solution. A pH of 7.0 means that the solution is neutral. A pH above 7.0 means the solution is basic; below 7.0 means the solution is acidic. Normal rainwater has a pH of 5.5. The National Center for Atmospheric Research has recorded storms in the north-eastern United States with a pH of 2.1, which is the acidity of lemon juice or vinegar. In Canada, Scandinavia, and the north-eastern United States, acid rain is blamed for the deaths of thousands of lakes and streams. These lakes have absorbed so much acid rain that they can no longer support the algae, plankton, and other aquatic life that provide food and nutrients for fish. Acid rain also damages buildings and monuments. Scientists are concerned that the deaths of thousands of trees in the forests of Europe, Canada, and the United States may be the result of acid rain.

Freon (CFC, or chlorofluorocarbon), various chemical compounds used as refrigerants.

Another new and troubling form of air pollution comes from a variety of chemicals called chlorofluorocarbons, also known as CFCs. These chemicals are used for many industrial purposes, ranging from solvents used to clean computer chips to the refrigerant gases found in air conditioners and ice boxes. CFCs combine with other molecules in the Earth’s upper atmosphere and then, by attaching themselves to molecules of ozone, transform and destroy the protective ozone layer. The result has been a sharp decline in the amount of ozone in the stratosphere. At ground level, ozone is a threat to our lungs, but in the upper atmosphere ozone works as a shield to protect against ultraviolet radiation from the sun. If the ozone shield gets too thin or disappears, exposure to ultraviolet radiation can cause crop failures and the spread of epidemic diseases, skin cancer, and other disasters. In late 1987, more than 20 nations signed an agreement to limit the production of CFCs and to work toward their eventual elimination.

Congress of the United States, legislative branch of the government, composed of Senate and House of Representatives.

Air pollution has been the target of some of the most complicated and far-reaching legislation ever enacted. In 1970, the United States Congress passed legislation aimed at curbing sources of air pollution and setting standards for air quality. A few years later, Congress passed laws designed to phase out the use of lead as an additive in gasoline. Since 1975, the level of lead in the average American’s bloodstream has declined. Further action against the causes of acid rain is continually debated in North America and throughout Europe.

Bhopal,India, capital of Madhya Pradesh state; formerly a Muslim state; ruled 1844-1926 by women (begums, or princesses); Sultan Jahan Begum (1858-1930) did much to advance position of women, education, and medical aid; in 1926 abdicated in favour of son; state acceded to India 1947; disaster in 1984 caused by leak of deadly gas from Union Carbide Corp. plant; pop. 309,285. Circa 1995.

Although the release of toxic chemicals into the atmosphere is against the law in most countries, accidents can happen, often with tragic results. In 1984, in Bhopal, India, a pesticide manufacturing plant released a toxic gas into the air that within a few hours caused the deaths of more than 2,000 people.

CLASSIFICATION

Insects belong to the phylum Arthropoda, one of the chief divisions of the animal kingdom. The name comes from two Greek words, arthron (“joint”) and podos (“foot”), and refers to the jointed feet. Arthropods also include spiders, lobsters, centipedes, and other animals. In this phylum, insects belong to the class Insecta. Each insect has two parts to its scientific name. For example, the housefly is Musca domestica. The first half of the name is that of the genus (a group of closely related species) to which the species domestica belongs. The many thousands of insect genera (plural of genus) are grouped under more than 900 families. These families, in turn, are grouped under as many as 30 orders.

To summarize, the housefly is classified as follows: kingdom, Animalia; phylum, Arthropoda; class, Insecta (Hexapoda); order, Diptera; family, Muscidae; genus, Musca; species, domestica. Each of these groups is often divided even further into subgroups (subphylum, subclass, suborder, and so on).

Ancestors of the Modern Insect

Insects appeared on Earth long before the advent of humans or the earliest mammals. The first insects probably evolved from primitive ringed worms. These insect ancestors were wingless and developed without metamorphosis, as do today’s silverfish.

The oldest fossils of ancestral insect forms are believed to be some 350 million years old. There are also fossil records, from later eras, of highly developed forms very similar to the mayflies, cockroaches, and dragonflies now in existence. Some ancient insects were truly huge; dragonflies, for example, had a wingspread of 2 feet (0.61 meter) or more.

THE IMPORTANCE OF INSECTS TO HUMANS

Insects that attack humans or anything of value to humans are termed pests; many of these are mutually competitive with humans for the world’s food supply. Other insects are benefactors of humans, as they devour the carcasses of dead animals, pollinate orchards, manufacture honey, or simply serve as another link in the food chain of the animal kingdom, for humans eat the animals including fish and birds which, in turn, live upon the insects.

HARMFUL INSECTS

About 10,000 species of insects have been classified as pests. Some are disease carriers, afflicting and often killing humans. Many insects prey upon domestic animals; others eat human food, clothing, and other possessions. Still others, in their quest for food or lodging, destroy trees, wood, and paper.

Carriers of Disease

 

Following are the names of some insects and the diseases they carry, and what may happen to someone who gets the disease.

INSECT	DISEASE CARRIED	RESULT
Tsetse fly	African sleeping sickness	Death
Mosquito	Yellow fever Encephalitis Malaria	Liver damage Death Chills Fever
Rat flea	Bubonic plague	Death
Human louse	Typhus	Fever Depression
Assassin bug	Chagas’ disease	Heart damage Brain damage Blindness

 

As vectors, or transmitting agents, of disease organisms, insects have caused more deaths and have inflicted greater misery and hardship on humankind than all the wars of history. In their efforts to find food, insects wage their own war against the human race. Some feed upon humans directly. Notable among these are the true flies, including mosquitoes, horseflies, black flies, tsetse flies, and other two-winged pests.

Perhaps humankind’s worst enemy among the insects is the mosquito. More lives have been lost as a result of malaria, yellow fever, encephalitis, and other mosquito-borne diseases than from all the other insect-borne diseases combined.

The tsetse fly has been a serious deterrent to the development of much of tropical Africa, for the insect acts as a vector of trypanosomiasis (African sleeping sickness) among humans and of nagana, a serious disease of livestock.

Horseflies and stable flies also transmit disease through their bites. The common housefly is not a biter, but it can carry myriad disease organisms on the hairs and the sticky secretions of its body. The assassin, or kissing, bug transmits the highly fatal Chagas’ disease.

Bedbugs, fleas, and lice live on the blood of birds and mammals, including humans. The human louse lives on the blood of humans alone and transmits typhus, relapsing fever, and trench fever.

The flea is potentially one of humankind’s deadliest enemies; rat fleas, for example, carry the germs of murine typhus and bubonic plague, which was instrumental in wiping out the lives of one fourth of the population of Europe in four years.

Household Pests

Insect pests in the home are most commonly chewers. One of the most troublesome of these the clothes moth attacks furs, woollens, and materials made of hair.

The silverfish and the fire-brat eat sized or stiffened material, such as the paper and bindings of books and starched clothing and curtains. In some parts of the United States, termites do considerable damage to furniture and paper products, as well as to the timber frameworks of buildings.

Plant-Eating Pests

Most insects are herbivorous that is, they feed on plants. Virtually every part of a plant, from the flower to the root, is vulnerable to their attack. They do their damage in a variety of ways.

Insects with chewing mouth-parts are the most destructive plant eaters. A horde of grasshoppers, for example, can strip every blade of vegetation from a field in a few hours. The destruction caused by other chewing insects, such as beetles, can also be enormous.

Insects with sucking mouth-parts, though usually smaller and less conspicuous than the chewers, also do a great deal of damage to farm crops and to forest and garden plants. These insects pierce plant tissues and draw out the vital juices. These insects include the aphids, chinch bugs, cicadas, and scale insects.

Damage is also done to the host plant from within by many other plant pests usually as larvae. Some eat their way between the top and bottom layers of a leaf, giving it a blotched appearance. The leaf roller, the larval form of certain moths, rolls a leaf into a tube and spins silk to hold it together. The caterpillar then feeds on the leaf. Other insect pests tie several leaves together into a large nest.

Gall-flies cause swellings on buds, flowers, leaves, stems, bark, or roots of plants. Usually the female pierces the plant and lays an egg; the plant then grows a gall, or swelling, around the egg.

Insect Immigrants Upset Nature’s Balance

As long as a region is left in its natural state, no species of insect is likely to increase disproportionately in numbers. The balance of nature prevents this from happening. Every insect has natural enemies, such as the spider, the praying mantis, and many kinds of disease organisms, that help keep the number of insects down.

The balance of nature in the New World was upset when settlers from Europe brought their domestic plants with them. Many insects that were harboured by these plants escaped the natural controls that were present in their old environments and became pests. The widespread use of such insecticides as DDT, now largely discontinued, also disrupted the balance of nature in some areas.

Pests arrive in many ways and from many lands. The gypsy moth, for example, was brought to the United States for experiments in the 1860s. It escaped from the laboratory and before the end of the 19th century had cost millions of dollars annually in damage to shade trees. The Argentine ant, an enemy of field crops and stored foods, was a stowaway in a cargo that reached New Orleans, La., in 1891. The brown-tail moth, another shade-tree pest, reached New England from Europe in about 1897. The alfalfa weevil came to Utah in 1902 in soil adhering to imported plants. The corn borer was carried from southern Europe in 1909 in a shipment of broom-corn Two serious pests came from Japan the Oriental fruit moth, on cherry trees presented by the city of Tokyo to Washington, D.C., in 1913; and the Japanese beetle, on trees reaching New Jersey in 1916. Also in 1916, carloads of cotton-seed from Mexico brought in the pink boll-worm Four arrived in 1920: the satin moth, an enemy of shade trees; the Asiatic beetle, which destroys lawns; the Mexican bean beetle, which feeds on a variety of beans; and the Mediterranean fruit fly, which is highly destructive of fruits, nuts, and vegetables.

METHODS OF INSECT CONTROL

Until the middle of the 19th century Americans were helpless against the growing insect menace. Finally, in the 1860s, arsenic compounds were found to be effective in combating the Colorado potato beetle. This was the first successful control of insect pests by scientific means. In the Morrill Act, in 1862, Congress provided for the study of insect pests and other agricultural problems.

Six principal methods are used in the control of insect pests. These methods are chemical, mechanical, radiological, cultural, biological, and legal.

Chemical. The chemical substances used to destroy insects are called insecticides. These may be broadly classified as stomach poisons, contact poisons, fumigants, and sorptive dusts. The stomach poisons are more effective against the chewing insects; the contact poisons, against sucking insects. Fumigants are gaseous poisons that enter the insect’s breathing system. Sorptive dusts are dry chemical compounds that kill insects by absorbing fatty substances from the exoskeleton, thus causing vital body fluids to evaporate.

Mechanical. Mechanical methods of insect control often primitive and time-consuming are generally less effective than chemical methods. They can seldom be applied practically to large populations of insects or over wide areas. These methods include swatting, the use of traps and barriers, water control, and temperature control. Water control involves adjustment of the water level or the rate of flow in breeding places. Temperature control is sometimes effective against insects that infest enclosed storage facilities. Reducing the temperature to 40 or 50 F (4 or 10 C) will cause most insects to become dormant; raising the temperature to 130 F (54 C) for three hours is sufficient to kill almost any insect.

Radiological. Perhaps the most dramatic, wholesale destruction of insects can be accomplished by making them infertile. Sexual sterility in male insects is induced by treating them with the rays of radioactive cobalt. If a large number of a particular species undergo this process in the laboratory, the treated males though sterile will still mate with fertile females; but the eggs laid by these females will be sterile. Following continual releases of sterile males in a single area, the number of young can be gradually reduced over a period of several generations until the population of the insect is totally wiped out within that area.

Through this technique the screw-fly, a serious pest of cattle, was first eradicated from the island of Curacao in the West Indies in 1954. Radiological warfare was then used to bring the screw-fly under control in the south-eastern United States.

Cultural. The cultural control of insect pests is of special interest to the farmer. Methods include the destruction of plant residues and weeds, crop tillage, crop rotation, and the growing of insect-resistant strains of crops.

Four things that farmers can do to control insects are

1. destroy plant residues and weeds. This can kill insects that are hibernating so they will not reproduce the following year.

2. crop tillage. This means to plough plants that have finished growing so they go back down into the soil and replenish the land. If a farmer ploughs at the right time of year, many insects living in the soil are killed.

3. crop rotation. This means to change the type of crop grown in a certain field in different seasons. Insect numbers are kept down when a farmer switches to a crop that insects do not like to eat.

4. insect-resistant strains. These are crops that insects do not like to eat. Developing insect-resistant strains of food limits insect populations.

When the farmer destroys the crop residues and weeds, he also destroys hibernating insects that would otherwise reproduce the following season. By ploughing or cultivating at the right time of year, he can often eliminate large numbers of harmful insects living in the soil. Crop rotation is an important means of combating insect pests of field crops, for many such pests will feed on only a single species or a single family of plant. Thus, if a farmer grows a grain one season and a legume the next, populations of many grain pests (as well as legume pests) can be kept down or eliminated.

Insect-resistant strains of many crops have been developed. Many of these strains have been developed by means of genetic engineering techniques. Resistance to the European corn borer, the wire-worm, and the chinch bug, for example, has been obtained in a single corn hybrid through selective breeding.

Biological. The control of insects by biological means involves the application of the pest’s natural enemies. These enemies may be microbes, mites, or other insects. Scientists have succeeded in controlling harmful insects by first determining the major predators or parasites of that insect in its country of origin. Then the scientists introduced these natural enemies as control agents in the new country that the pest had infested. A classic example is the cottony cushion scale, which threatened the survival of the California citrus industry in 1886. The predatory ladybird beetle, or vedalia beetle, was introduced from Australia, and within two years the scale insect had virtually disappeared from California.

In eastern Canada in the early 1940s the vicious European spruce sawfly was completely controlled by the spontaneous appearance of a viral plant disease, perhaps unknowingly introduced from Europe. This event led to increased interest in plant diseases as potential means of pest control.

Legal. The legal control of insects concerns government regulations to prevent the spread of insect pests from one country or region to another. The Federal Plant Quarantine Act of 1912 began the fight against imported pests by providing for inspectors at ports of entry. These officials examine all plant products as well as passengers’ baggage. Infested material is destroyed or thoroughly fumigated. Aircraft are examined and may be fumigated as soon as they arrive in the United States from countries where insect pests are a potential threat.

By the time an immigrant pest is discovered in domestic plants, it is usually too late for eradication of the injurious insect. In some instances, however, control has been achieved. In 1929 the Mediterranean fruit fly was detected in Florida orchards; the insects threatened ruin to the fruit crop. State and federal entomologists united for battle, and all Florida was quarantined. Abandoned and run-down orchards were destroyed. Chemists developed new poison sprays. By the end of the summer not a “medfly” could be found in Florida. In 1956 a second such outbreak occurred; this too was put down after several months of intensive warfare.

In 1981 a serious spread of the medfly threatened California’s agricultural regions with economic disaster. The pest had been imported accidentally in 1980. An attempt to control the insects by importing sterilized males from Peru failed. The Department of Agriculture threatened to quarantine the state’s produce unless the infected areas were fumigated. Governor Jerry Brown finally authorized helicopter spraying of the pesticide called malathion in July 1981. The spraying halted the threat to the California crops.

BENEFICIAL INSECTS

Numerous species of plants depend upon insects to pollinate them. In visiting flowers for nectar, insects carry pollen from one flower to the pistil of another. In this way they fertilize the plant and enable it to make seeds.

Without insects there would be no orchard fruits or berries. Tomatoes, peas, onions, cabbages, and many other vegetables would not exist. There would be no clover or alfalfa. The animals that need these forage crops would be of poor quality, and humankind’s meat supply would suffer. There would be no linen or cotton; no tea, coffee, or chocolate.

The honeybee produces honey and wax. Silk is made by the silkworm larva. Shellac is secreted by an Oriental scale insect. Such insects as the dobsonfly are used in sport fishing as bait.

In many underdeveloped areas of the world grasshoppers, caterpillars, and other insects are necessary to humans as food. Insects are also important to humans as food for other animals. Freshwater fishes depend upon insects for food. Hundreds of species of birds would perish if there were no insects to eat.

Insects have also played a significant role in the biological laboratory. The Drosophila fly, in particular, has been valuable in the study of inherited characteristics. The European blister beetle, or Spanish fly, is helpful in the fight against human disease, for it secretes cantharidin, a substance used medically as a blistering agent.

Many insects are invaluable as predators on insects that are pests to humans. In the same way, plant-eating insects are often valuable for their destruction of weeds. Insects that burrow in the earth improve the physical and chemical condition of the soil.

As scavengers, insects perform the important function of eating dead plants and animals. The housefly, scorned as a disease carrier, is beneficial in its larval form the maggot. It feeds on decaying refuse and in this way makes the world somewhat cleaner and more habitable for others.

The Principal Insect Orders

In the following list are the principal orders within the two subclasses of the class Insecta. Several obscure orders with relatively few species are omitted. The orders of the most primitive groups are given at the beginning of the list; the most highly developed at the end. After the name of each order, its meaning is given. The suffix -ptera means “wing”; -aptera, “wingless”; -ura, “tail.”

Subclass Apterygota

(wingless, no metamorphosis)

Thysanura (“tassel tail”) silverfish, bristle-tails, and fire-brats; wingless, scaly, three long bristles at the end of the body.

Collembola (“glue bolt”) spring-tails; tiny, wingless; jump by means of a springlike appendage below the abdomen.

Subclass Pterygota

(winged, undergo metamorphosis)

The following 11 orders are sometimes known as the Exopterygota. These have incomplete metamorphosis.

Orthoptera (“straight wings”) cockroaches, grasshoppers, crickets, walking-sticks, mantids, katydids, locusts, and their allies; fore-wings leathery; hind wings folded fan-wise

Dermaptera (“skin wings”) earwigs; fore-wings short; abdomen ends in a forceps-like appendage.

Plecoptera (“braided wings”) stone flies; membranous wings fold flat over the back; aquatic nymphs breathe with gills.

Isoptera (“equal wings”) termites; social insects with a caste system; resemble ants but have a broad, rather than narrow, waist.

Psocoptera (“gnawers”) psocids, book lice, and their allies; winged or wingless; feed on books and museum specimens.

Mallophaga (“wool eaters”) biting lice; flat, with chewing mouth-parts; external parasites of birds and certain warm-blooded animals.

Ephemeroptera (“living but a day”) mayflies; night-flying, delicate, short-lived; with membranous wings and two or three long tail filaments; nymphs aquatic; adults do not feed.

Anoplura (“unarmed tail”) sucking lice; with piercing mouth-parts for feeding on blood; external parasites of mammals.

Thysanoptera (“fringed wings”) thrips; usually four minute narrow fringed wings; pests of cultivated plants, spread viral plant diseases.

Hemiptera (“half wings”) (includes the order Homoptera) true bugs, aphids, leaf-hoppers, scales, and their allies; mostly four-winged, with piercing or sucking mouth-parts; many are plant pests.

Odonata (“toothed”) dragonflies and damselflies; two similar pairs of long, narrow wings; dragonflies keep wings outstretched at rest, damselflies keep them together over the back.

The remaining orders are sometimes known as the Endopterygota. These have complete metamorphosis.

Neuroptera (“nerve wings”) lacewings, ant lions, snake flies, and dobsonflies; two similar pairs of large, membranous wings, usually folded roof-like over the body when at rest.

Mecoptera (“long wings”) scorpion flies; long-faced, narrow-winged; in some males tip of abdomen curls over the back as a scorpion’s does.

Trichoptera (“hair wings”) caddis flies; adults moth-like but with longer antennae and uncoiled proboscis; larvae aquatic, make fixed or portable cases in which they live and pupate.

Lepidoptera (“scale wings”) moths and butterflies; wings covered with minute, overlapping scales; coiled proboscis usually present.

Coleoptera (“sheath wings”) beetles and weevils; fore-wings hard, vein-less, and opaque, meeting in a straight line; hind wings membranous, translucent; the largest order of insects, numbering some 300,000 species.

Strepsiptera (“twisted wings”) males winged, females wingless; females of most species are parasites on other insects.

Hymenoptera (“membrane wings”) wasps, ants, bees, and their allies; many species useful to man; ovipositors in some females modified as a stinger.

Diptera (“two wings”) true flies, mosquitoes, and midges; two developed wings; mouth-parts variable; many species pupate inside the last larval skin.

Siphonaptera (“siphon wingless”) fleas; tiny, jumping insects with narrow bodies adapted for moving between the hairs of animal hosts, whose blood they suck; some species transmit disease.

Assisted by Thomas Park, Professor Emeritus of Biology, University of Chicago; former President, Ecological Society of America. Critically reviewed and updated by J. Whitfield Gibbons, Senior Research Ecologist and Professor of Zoology, Savannah River Ecology Laboratory, University of Georgia.

BIBLIOGRAPHY FOR INSECT

Barbosa, Pedro and Jack Schultz. Insect Outbreaks (Academic Press, 1987).

Better Homes and Gardens Editors. Bugs, Bugs, Bugs (BH&G, 1989).

Blum, Murray. Fundamentals of Insect Physiology (Wiley, 1985).

Borror, Donald. An Introduction to the Study of Insects (Saunders College Publications, 1989).

Boy Scouts of America. Insect Study (BSA, 1985).

Burton, John. The Oxford Book of Insects (Oxford, 1982).

Gattis, L.S. Insects for Pathfinders (Cheetah Publications, 1987).

Goor, Ron and Nancy Goor. Insect Metamorphosis (Macmillan, 1990).

Higley, Leon. Manual of Entomology and Pest Management (Macmillan, 1989).

Horton, B.G. and others. Amazing Fact Book of Insects (Creative Editors, 1987).

Leahy, Christopher. Peterson Field Guide to Insects (Houghton, 1987).

Line, Les and Lorus Milne. The Audubon Society Book of Insects (Abrams, 1983).

Mayer, Daniel and Connie Mayer. Bugs: How to Raise Insects for Fun and Profit (And Books, 1983).

Seymour, Peter. Insects: A Close-Up Look (Macmillan, 1985).

Stiling, Peter. An Introduction to Insect Pests and Their Control (Macmillan, 1985).