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. any of a large family (Aphididae) of small, soft-bodied homopteran insects that suck the juice from plants.

On a stem or on the underside of a leaf sometimes a crowded colony of plant lice, or aphids, may be visible. They are parasites that have sharp sucking beaks and live on the sap of plants. There are many kinds. Most feed exclusively on a particular crop, weed, or tree.

The smallest aphids measure about 1/20 of an inch (0.13 centimetre) in length and the largest about 1/14 of an inch (0.64 centimetre). Most species are green, but some are pink, white, brown, or black. Those that migrate are born with wings. Most generations are made up of wingless females. During the feeding season these females, without mating, produce living young that are all females and that themselves produce several generations of young during the summer. In the fall a generation is born that includes both males and females. After mating, the females of this generation lay eggs that will hatch in the spring to start new colonies.

Aphids secrete from the alimentary canal a sweet watery liquid that is called honeydew. Ants relish this as food. Some species of ants care for whole herds of aphids (so-called “ants’ cows”). The ants build mud shelters for them at the roots of plants and move them often to new pastures as the old ones wither. To induce the flow of honeydew the ants milk the “cows” by stroking them with the antennae. Most aphids, particularly the woolly aphids, spread a white, waxy secretion over themselves for protection.

Many aphids suck plant sap or inject poisonous saliva into plants, causing the plants’ leaves to curl and sometimes drop off. Some aphids produce gall-like swellings on roots and bark. One of the most destructive aphids is the green bug, which infests oats, wheat, and other small grains. Fields of corn are often destroyed by the corn-root aphis, which is dependent on the cornfield ant for survival.

Aphids reproduce so rapidly that if unchecked they can destroy entire fields of crops. Their numbers may be controlled by such natural enemies as ladybird beetles (ladybugs), aphid lions, and lacewings. Farmers frequently control the insects by spraying with pest-control agents. Aphids belong to the order Homoptera and the family Aphididae.

Water Pollution

Since the beginning of civilization, water has been used to carry away unwanted refuse. Rivers, streams, canals, lakes, and oceans are currently used as receptacles for every imaginable kind of pollution. Water has the capacity to break down or dissolve many materials, especially organic compounds, which decompose during prolonged contact with bacteria and enzymes. Waste materials that can eventually decompose in this way are called biodegradable. They are less of a long-term threat to the environment than are more persistent pollutants such as metals, plastics, and some chlorinated hydrocarbons. These substances remain in the water and can make it poisonous for most forms of life. Even biodegradable pollutants can damage a water supply for long periods of time. As any form of contamination accumulates, life within the water starts to suffer. Lakes are especially vulnerable to pollution because they cannot cleanse themselves as rapidly as rivers or oceans.

A common kind of water pollution is the effect caused by heavy concentrations of nitrogen and phosphorus, which are used by plants for growth. The widespread use of agricultural fertilizers and household detergents containing these elements has added large amounts of plant nutrients to many bodies of water. In large quantities, nitrogen and phosphorus cause tiny water algae to bloom, or grow rapidly. When the algae die, oxygen is needed to decompose them. This creates an oxygen deficiency in the water, which causes the death of many aquatic animals. Plant life soon reduces the amount of open water. These events speed up the process of eutrophication, the ageing and eventual drying up of a lake.

Sedimentation also pollutes water. It is the result of poor soil conservation practices. Sediment fills water-supply reservoirs and fouls power turbines and irrigation pumps. It also diminishes the amount of sunlight that can penetrate the water. In the absence of sufficient sunlight, the aquatic plants that normally furnish the water with oxygen fail to grow.

Factories sometimes turn waterways into open sewers by dumping oils, toxic chemicals, and other harmful industrial wastes into them. In mining and oil-drilling operations, corrosive acid wastes are poured into the water. In recent years, municipal waste treatment plants have been built to contend with water contamination. Some towns, however, still foul streams by pouring raw sewage into them. Septic tanks and cesspools, used where sewers are not available, may also pollute the groundwater and adjacent streams, sometimes with disease-causing organisms. Even the purified effluent from sewage plants can cause water pollution if it contains high concentrations of nitrogen and phosphorus. Farm fertilizers in some regions fill groundwater with nitrates, making the water unfit to drink. Agricultural run-off containing dangerous pesticides and the oil, grime, and chemicals used to melt ice from city streets also pollute waterways.

Land and Soil Pollution

In order to sustain the continually growing human population, current agricultural methods are designed to maximize yields from crop lands In many areas, the overuse of land results in the erosion of topsoil. This soil erosion, in turn, causes the over-silting or sedimentation of rivers and streams.

One of the most hazardous forms of pollution comes from agricultural pesticides. These chemicals are designed to deter or kill insects, weeds, fungi, or rodents that pose a threat to crops. When airborne pesticides drift with the wind or become absorbed into the fruits and vegetables they are meant to protect, they can become a source of many illnesses, including cancer and birth defects.

Pesticides are often designed to withstand rain, which means they are not always water-soluble, and therefore they may persist in the environment for long periods of time. Some pests have developed a genetic resistance to these chemicals, forcing farmers to increase the amounts or types of pesticide.

The pesticide DDT provides the best-known example of the dangers of introducing synthetic chemical compounds into the environment. Chemically a chlorinated hydrocarbon, DDT was widely used for many years after World War II. At first it was highly regarded because it reduced the incidence of malaria throughout the world. Then, evidence began to show that DDT might be doing more harm than good. DDT, like other chemically stable pesticides, is not readily biodegradable. It has been found in the tissues of every organism tested for its presence. DDT is now known to affect biological activities. It reduces the rate of photosynthesis in marine phytoplankton, organisms that form the basis of most ocean food chains.

Although DDT has been banned in the United States and most other countries, it is still manufactured and used in some parts of the world. Many other pesticides also have been banned. Thousands of pesticides remain in use and, in some cases, their agricultural value may balance out their risks.

Some urban areas are beginning to experience a serious problem regarding the disposal of garbage and hazardous wastes, such as solvents and industrial dyes and inks. In many areas landfill sites are approaching their full capacity and many municipalities are turning to incineration as a solution. Giant high-temperature incinerators have become another source of air pollution, however, because incineration ashes sometimes contain very high concentrations of metals as well as dioxins, a dangerous family of chemical poisons.

One answer to the garbage problem is recycling. Some towns have passed ordinances that encourage or require residents to separate glass and aluminium cans and bottles from other refuse so that these substances can be melted down and reused. Although lightweight steel, cardboard, and paper are also economically recyclable, most industries and cities still burn or bury large amounts of scrap metal and paper products every day.

Radioactive Pollutants

Cosmic rays, highly penetrating radiations reaching the Earth from outer space.

Radioactivity has always been part of the natural environment. An example of natural radioactivity is the cosmic radiation that constantly strikes the Earth. This so-called background radiation has little effect on most people. Some scientists are concerned, however, that humans have introduced a considerable amount of additional radiation into the environment.

Since the first atomic bomb was dropped on Hiroshima, Japan, on Aug. 6, 1945, there has been an increased awareness of the environmental threat posed by nuclear weapons and radioactive fallout. Many scientists are concerned about the long-term environmental impacts of full-scale nuclear war. Some suggest that the large amounts of smoke and dust thrown into the atmosphere during a nuclear explosion would block out the sun’s light and heat, causing global temperatures to drop.

Even the testing of nuclear weapons directly affects the environment. Such tests are rarely conducted above ground or in the ocean. International concern over the effects of these tests led the United States, Great Britain, and the Soviet Union to sign the Nuclear Test-Ban Treaty in 1963.

On April 26, 1986, the Chernobyl nuclear power plant in the Soviet Union malfunctioned creating the worst peacetime nuclear disaster. Many details of the Chernobyl accident remain undisclosed, but it is known that the radioactive core of the power plant became exposed, and there was a partial meltdown, releasing large amounts of radioactive materials. Because the medical effects of exposure to nuclear radiation can take years to become apparent, it is not yet known how many additional cases of cancer, birth defects, and skin disease will have been caused by the Chernobyl accident.

Another immediate environmental problem is the disposal of nuclear wastes. Some radioactive substances have a half-life of more than 10,000 years, which means they remain radioactive and highly dangerous for many thousands of years. In nuclear physics, a half-life is the period of time required for the disintegration of half of the atoms in a sample of a radioactive substance. Science has not yet found a safe method of permanent disposal of high level radioactive wastes. Even temporary storage of these wastes is a dangerous and expensive problem. Experiments are under way to investigate the possible use of salt mines several thousand feet below the surface of the Earth as repositories for spent nuclear fuel rods and similar highly radioactive substances.

Thermal, or Heat, Pollution

While the concept of heat as a pollutant may seem improbable on a cold winter day, at any time of year an increase in water temperature has an effect on water life. Heat can be unnaturally added to streams and lakes in a number of ways. One is to cut down a forest completely. The brooks and streams that flowed through it are then exposed to the sun. Their temperatures begin to rise. As they flow into larger bodies of water, these in turn are warmed. This can kill fish and other water animals incapable of tolerating the higher temperatures.

Heat pollution is a consequence of the rising energy needs of man. As electric power plants burn fossil fuels or nuclear fuel to provide this energy, they release considerable amounts of heat. Power plants are usually located near bodies of water, which the plants use for heat-dissipation purposes. Some stretches of the Hudson River in New York no longer freeze in winter because of the flow of hot water into the river from adjacent power plants. Living things especially such cold-blooded animals as fish are very sensitive to even small changes in the average temperature. Because of the added heat in waters affected by power plants, many aquatic habitats may be undergoing drastic change. In some instances, the warmer water may cause fish eggs to hatch before their natural food supply is available. In other instances, it may prevent fish eggs from hatching at all.

In addition, a very small rise in the average temperature of the Earth’s surface could produce profound climatic changes. Some experts believe that it would cause the Greenland and Antarctic ice caps to melt, raising ocean levels and inundating large areas of land.

Average worldwide temperatures can be affected when the products of combustion carbon monoxide, water vapour, and carbon dioxide are emitted into the air, especially at high altitudes. Since the normal level of carbon dioxide in the air is quite small, any significant addition is a potential threat. Although solar energy on its way to the Earth’s surface easily passes through layers of carbon dioxide, some of the heat escaping from the Earth would be absorbed by increased amounts of atmospheric carbon dioxide, much as heat is trapped in a greenhouse. A worldwide greenhouse effect of this type might produce a dangerously warmer world. Since the late 19th century, the average global temperature has increased between 0.54°F and 1.08°F (0.3°C and 0.6°C). Internationally, 1990 was the hottest year on record since official weather records first started being kept by the British in about 1860.

Noise Pollution

The hearing apparatus of living things is sensitive to certain frequency ranges and sound intensities. Sound intensities are measured in decibels. For example, a clap of thunder has an intensity of about 100 decibels. A sound at or above the 120-decibel level is painful and can injure the ear. Noise pollution is becoming an unpleasant fact of life in cities, where the combination of sounds from traffic and building construction reverberates among high-rise buildings, creating a constant din.

In addition, the intense volume at which some popular music, especially heavy metal rock music, is played has resulted in the loss of some or all of the hearing of a few musicians and members of their audiences. There is some evidence that extreme levels of noise can produce other deleterious effects on human health and on work performance.

Efforts to Halt Pollution

The solution of some pollution problems requires cooperation at regional, national, and international levels. For example, some of the acid rain that falls in Canada is caused by smokestacks of coal-burning power plants in the United States. Thus, rejuvenating the lakes of eastern Canada requires the cooperation of electric utilities in Indiana and Ohio.

Greenpeace Foundation, international organization for the protection of the environment.

In the United States laws have been passed to regulate the discharge of pollutants into the environment. The Environmental Protection Agency (EPA), which was formed through the National Environmental Policy Act (NEPA) of 1969, oversees most federal anti pollution activity. The National Environmental Policy Act also mandated the use of environmental impact statements, which require that businesses or governments examine alternatives and acknowledge the possible harmful effects of such activities as opening new factories, building dams, and developing new oil wells. With the advent of massive oil spills from supertankers, the washing up of medical wastes on shores in New York and New Jersey, and an increased build-up of toxic wastes, such international organizations as Greenpeace have become ever more dedicated to preventing environmental abuses and heightening public awareness of environmental issues.

The Clean Air Act, the Safe Drinking Water Act, and the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (known as Super fund) are among the laws that set standards for healthy air and water and the safe disposal of toxic chemicals. In 1990 President George Bush signed the Clean Air Act of 1990, the second amending legislation since the original Clean Air Act of 1970. The new law called for reductions in emissions of sulphur dioxide and nitrogen oxide by half, carbon monoxide from vehicles by 70 percent, and other emissions by 20 percent. The number of toxic chemicals monitored by the EPA would increase from 7 to about 250, and industry would be required to control their waste release by means of the best technology available. In the same year, the California Air Resources Board introduced the strictest vehicle-emission controls in the world. By 2003 the hydrocarbon emission of all new cars sold in California would have to be at least 70 percent less than that of 1993 models, and by 1998, 2 percent of all cars (rising to 10 percent by 2003) would have to release no harmful emissions at all. Several North-eastern states followed suit by introducing similar, though slightly less severe, controls.

Assisted by John H. Thomas, professor of biology at Stanford University, and Paul J. Allen, Director of Communications at the Natural Resources Defense Council, Washington, D.C.

BIBLIOGRAPHY FOR ENVIRONMENTAL POLLUTION

Caplan, Ruth. Our Earth, Ourselves (Bantam, 1990).

Carson, Rachel. Silent Spring (Houghton, 1987).

Luoma, Jon. The Air Around Us (Acid Rain Foundation, 1989).

Mott, Lawrie and others. Pesticide Alert (Sierra Club and National Resource Defense Council, 1988).

Newton, David. Taking a Stand Against Pollution (Watts, 1990).

Thackray, Sue. Looking at Pollution (David and Charles, 1987).

Trager, Oliver, ed. Our Poisoned Planet: Can We Save It? (Facts on File, 1989).

Tripathi, A.K. and Pandey, S.N. Water Pollution (South Asia Books, 1990).

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).