The Bugs Are Coming

The struggle between man and insects began long before the dawn of civilization, has continued without cessation to the present time, and will continue, no doubt, as long as the human race endures. We commonly think of ourselves as the lords and conquerors of nature. But insects had thoroughly mastered the world and taken full possession of it before man began the attempt. They had, consequently, all the advantage of possession of the field when the contest began, and they have disputed every step of our invasion of their original domain so persistently and successfully that we can even yet scarcely flatter ourselves that we have gained any very important advantage over them. If they want our crops, they still help themselves to them. If they wish the blood of our domestic animals, they pump it out of the veins of our cattle and our horses at their leisure and under our very eyes. If they choose to take up their abode with us, we cannot wholly keep them out of the houses we live in. We cannot even protect our very persons from their annoying and pestiferous attacks, and since the world began, we have never yet exterminated--we probably shall never exterminate--so much as a single insect species.

This gloomy view of man's perennial adversaries was written 60 years ago by U.S. Entomologist S.A. Forbes, but his modern counterparts would be hard pressed to find fault with it today. Despite mind-boggling advances in science and technology over the past several decades--the harnessing of nuclear energy, the mastery of space flight, the breaking of the genetic code--humankind has made little progress in its age-old battle with bugs. For a brief time after World War II, newly developed chemical pesticides gave scientists hope that the ultimate weapon against insects had been developed. Indeed, the bugs were sent temporarily into unprecedented retreat.

Now, however, all over the U.S. and in many areas around the globe, bugs are on the march, relentlessly not only retaking the ground so recently won by Homo sapiens but also making new advances. Aided by Government restrictions on pesticides as well as their own growing immunity to the chemicals, and benefiting further from the miscalculations and complacency of their human enemies, insects seem well on their way to fulfilling the chilling prophecy of The Hellstrom Chronicle: "If any living species is to inherit the earth, it will not be man."

In the U.S., the South American fire ant has advanced from its initial beachhead--Mobile, Ala., in 1918--and now infests some 150 million acres in nine Southern states, injuring and sometimes killing livestock with its fiery sting and driving farm workers from the fields. Some experts believe that it will continue to press forward, adapting to cooler temperatures and inexorably moving toward both the North and the West. In forest areas, the gypsy moth, the tussock moth, the spruce budworm and the southern pine beetle are wreaking devastation on huge areas of woodland, defoliating and killing millions of valuable trees and destroying in 1975 alone enough board feet of timber to build 910,000 houses.

Corn borers and rootworms are attacking crops in the Midwest corn belt at a prodigious rate, and the boll weevil--between crop loss and control measures--annually costs U.S. farmers $260 million. Insects destroy some 10% of all crops grown in the U.S., causing between $5 billion and $6 billion in losses. Besieged modern-day farmers can still appreciate the doggerel composed by the early American pioneer to explain why he planted four kernels of corn for every plant he hoped to harvest: "One for the maggot/ One for the crow/ One for the cutworm/ And one to grow." Each year across the land, millions of people are stung and bitten by insects. Some of these victims die from their reaction to the bite or from the disease transmitted by it. The U.S. may some day have another bothersome bug: descendants of the high-strung and aggressive "killer bee." Imported from Africa and accidentally released in Brazil--where it bred with honeybees of European origin--this fierce hybrid is moving northward at a rate of as much as 200 miles a year, without provocation attacking and sometimes killing both animals and humans. It has now reached the Amazon delta.

In other parts of the world, insects are also on the offensive. Malaria, transmitted by mosquitoes and not long ago almost eliminated from many regions, is returning with a vengeance. It strikes 100 million people a year in sub-Saharan Africa, killing 800,000--most of them children under five. River blindness, carried by a species of black fly, afflicts a million Africans yearly in the Volta River basin alone, leaving 700,000 of them sightless. The tsetse fly, bearer of sleeping sickness, continues to dominate a large part of the continent. Says John Strangways-Dixon, a deputy director of Nairobi's International Center of Insect Physiology and Ecology: "The fly has taken over in 25% of Africa. I can't think of any other insect that has got man so tied down."

Agricultural pests also plague the developing nations of Africa. Tanzanian authorities estimate that insects destroy 25% of their country's crops after harvesting; in Kenya, officials estimate that 75% of the nation's crops is lost to insects. Larvae of shootflies ruin sorghum crops, depriving the region of an important source of protein. Army worms (the destructive larvae of a species of moth) are currently on the march in east Africa. "The worms reduced my half-acre field of wheat to stubble overnight," lamented a Kikuyu farmer in Kenya, adding: "Insecticides are beginning to cost almost as much as I get for my few bags of grain." One locust swarm observed in eastern Africa was 100 ft. deep along a mile-wide front, covered the sky like a great black cloud and took nine hours to pass a given point.

Clearly, the trend is not running in man's favor. "If we keep on going the way we are, in the end man will be gone and all that will be left will be a few bugs, some amoebae and a couple of rats scampering around," says Robert van den Bosch, an entomologist on the Berkeley campus of the University of California. "We are losing the war against bugs."

Man's most formidable adversaries are included by scientists in a phylum, or group, called arthropods--from the Greek for jointed feet. Insects differ in several important respects from other members of this phylum, which also includes crustaceans such as the lobster and crab and the arachnids (scorpions, ticks and spiders). Lobsters and crabs, for example, have five pairs of walking legs; millepedes may have two hundred pairs. But all insects, like Gaul, are divided into three parts, or segments--a head, a thorax or chest, and an abdomen. All have three pairs of legs, and most of them have wings.

Within those limitations, however, insects come in all shapes and a variety of sizes. Entomologists estimate that there may be as many as 5 million insect species, of which fewer than a million have been identified and named (there are, for example, more than 300,000 species of beetles alone). Insects range in size from those no larger than a dust particle, and a species of hairy winged beetle that can crawl through the eye of a needle, to the Atlas moth of India, which has a 12-in. wingspan, almost as large as an oriole's. Brian Hocking of Canada's University of Alberta gives an estimate in his book Six-Legged Science that the insect population of the world is at least 1,000,000,000,000,000,000 and, taking the weight of each insect as a not unreasonable 2.5 milligrams (less than one ten-thousandth of an ounce), he figures that the weight of the earth's insect population exceeds that of its human inhabitants by a factor of twelve.

The insect made its appearance on earth some 400 million years ago, and in the intervening time has become well equipped to survive. (In fact, the durable cockroach evolved into something very similar to its current unpleasant form some 320 million years ago and apparently saw little need for further improvement.) An insect has a strong exterior skeleton and seems disproportionately powerful in relation to its size (an ant can lift 50 times its own weight). Its capacity for flight (most but not all insects can fly), attained about 100 million years before the first flying reptiles or birds, enables it to escape its enemies and range far and wide in search of food. The insect's small size frees it from the need to compete with many larger animals for a place in the environment; its simple physiology enables it to endure conditions that kill other animals. Some insects can survive temperatures as low as -- 30DEG F, or as high as 120DEG F.

The insect's life cycle is also an asset to its survival. Many insects are completely metamorphic, passing from egg through larval, pupal and sometimes suspended stages before developing into full-fledged adults that can then mate and start the process all over again. This enables them to take advantage of a wide variety of food supplies. Insect fecundity is frightening. Many species lay hundreds or thousands of eggs after each mating. Some pass through their entire life cycles, from egg to adult, in a matter of days or weeks, producing dozens of generations a season. This gives them an enormous evolutionary advantage, as scientists have learned to their dismay. If only a tiny fraction of a species has resistance to a new man-made spray that wipes out the remainder, for example, the few survivors can quickly multiply into a huge insect population with built-in immunity to the insecticide.

Insect senses are also highly specialized for survival.

Multifaceted compound eyes, often mounted on the ends of posts or stalks, give bisects something approaching 360DEG vision, as anyone who has tried to swat a housefly can verify. Their sensitive antennae enable them to smell food sources or find mates; some insects can smell the sex pheromones, or attractants, emitted by females of their species more than 15 miles away.

Most insects lead solitary, asocial lives and spend their brief days on earth trying desperately to be diners rather than dinners. Some species, however, live in societies so well structured that humans might profit by emulating them. Honeybees group together in hives or colonies that might be compared to the human body--the queen, the only fertile female in a hive, functioning as the reproductive system; the workers, or sterile females, who gather nectar and feed the young, as the arms, legs and digestive tract; the drones, whose sole function is to fertilize the queen, as the heart that keeps the system going.

Some wasps are also highly social, building houses of paper, which they make by chewing up plant material and mixing it with saliva, and living together in harmony. The most social and best organized of all insects are the ants.

Divided into castes that include workers, soldiers and immature young, ants carry out a wide variety of organized activities. Ordinary garden ants herd aphids, which they milk for their sweet nectar. Some species of ants farm, tending crops of tiny fungi in their underground chambers; others take and keep slaves from rival ant colonies. Species like the driver ants of Africa and the army ants of South America conduct military campaigns with a precision that any general would envy, advancing in columns protected by soldiers over routes carefully scouted by advance parties. Ants are also accomplished architects; African termites, for example, build mounds with thick walls that keep the air inside at a constant temperature all year round. Some species of ants apparently share the human characteristic of using tools. Joan and Gary Fellers of the University of Maryland reported recently in Science that four species of ants seem to use pieces of leaf, mud and sand grains as tools to carry soft foods from distant sources back to the colony, an efficient practice that enables them to compete more successfully with other species of ants.

Insects, like other creatures, hold well-defined places in nature's scheme of things. They are a crucial link in the food chain, providing a large part of the diets consumed by fish, small mammals and birds; some species of birds, for example, have been threatened with extinction when natural causes or man-made pesticides kill the insects that they feed upon.

Some insects are also useful to man and important to agriculture. Nectar-sucking insects, especially bees, pollinate flowering plants, and bees are the source of the honey that sugar-loving humans consume in great quantities each year. Other insects are also considered beneficial. The attractive red and black ladybird beetle, or ladybug, celebrated in the nursery rhyme, eats aphids and other small insects--to the gardener's delight. Before the development of dyes made from coal-tar derivatives, a scale insect provided the world with red dye; other species of scale insects are still used in the manufacture of shellac. The flesh-eating larvae of the dermestid beetle are used by museums to strip clean the bones of animals so that their skeletons can be mounted for display. Ancient Egyptians venerated the scarab beetle as a symbol of immortality; among its other activities, the insect breaks up and carries away animal and human droppings that might otherwise provide breeding grounds for dis ease. With rare exceptions, however, man through the ages has been instinctively entomophobic, or afraid of insects. Not for nothing did the ancient Israelites give Beelzebub, or Satan, the title of "Lord of the Flies."

Efforts to control the ravages of insects are as old as civilization itself. During the classical era, citizens of Cyrene, on the coast of what is now Libya, were required to turn out three times a year to fight locusts by crushing them. During the Middle Ages, people frequently relied on ecclesiastical courts to control infestation by pests. In 1120 the Bishop of Leon in France excommunicated the caterpillars that were consuming local crops. In 1488 the high vicar of Autun took a similar step; he directed priests of neighboring parishes to order weevils to stop their attacks on grainfields and to excommunicate the insects. Undeterred, the weevils ate on.

Desperate for a defense against insects, man began to develop chemical controls. During the late Middle Ages, people attempted to control tree-destroying insects by exposing the roots of afflicted trees, pouring in old wine lees and then closing the hole. Infusions of tobacco were used in France as early as 1690 to fight lace bugs on pear trees. Pyrethrum, a compound obtained from the chrysanthemum family, was used as far back as 1800 to kill fleas. Rotenone, which can be extracted from various plants, was introduced in 1848 to attack leaf-eating caterpillars. Synthetic insecticides were introduced during the 19th century, and one--Paris green--was used against the Colorado potato beetle in the U.S. during the 1860s.

The single most significant development in insect control was the discovery of a compound with the unpronounceable name of dichlorodiphenyltrichloroethane, or, as it came to be known, DDT. First synthesized in 1874, the chemical languished in the laboratory until 1939, when Chemist Paul Miiller of Switzerland's J.R. Geigy chemical company discovered its insecticidal properties. The U.S. Army considered the chemical so effective that it classified it "top secret," and first used it against a typhus epidemic in Naples, Italy, in 1943. It worked so well that the military promptly began applying DDT against a wide variety of insects responsible for spreading malaria, typhus, cholera and encephalitis. Says Berkeley's Van den Bosch (who now opposes widespread reliance on chemical insecticides): "DDT was beautiful. It was cheap and it killed just about everything."

DDT's success prompted the introduction after World War II of a host of similar chlorine derivatives, including chlordane, heptachlor, aldrin, dieldrin, toxaphene and endrin. Wartime research on nerve gases also led to the development of a whole family of phosphorus-based insecticides, such as parathion, malathion and dimethoate, which, unlike DDT and other chlorine-based compounds, tended to break down more quickly into innocuous substances in the soil.

The introduction of these insecticides had a remarkable effect on agriculture, which for the first time in history could be relatively bug free. Through insecticides alone, U.S. farmers increased their crop yields by some 10% in the years between 1940 and 1975. Their counterparts in Africa and Asia also began to make some headway in the battle against bugs, as did public health authorities. Widespread spraying of mosquito breeding areas slashed the incidence of malaria in Italy and other Mediterranean lands and made inroads against the disease on the Indian subcontinent.

But pesticides proved to be a mixed blessing. Beginning in the late '40s, researchers began to discover traces of DDT --which degrades, or breaks down, very slowly--in the tissue of fish, wildlife and humans. At about the same time, scientists began to report that the chemical was causing some species of birds to lay eggs with abnormally thin shells that broke during brooding; as a result, the numbers of ospreys, peregrine falcons, bald eagles and brown pelicans were declining. These revelations were followed by the publication in 1962 of Rachel Carson's book, Silent Spring, which began to crystallize anti-insecticide sentiment. But the coup de grace was administered by later studies showing that DDT could cause cancer in laboratory animals. Deciding that the compound was a hazard to humans, the Environmental Protection Agency ordered DDT sales to be restricted in 1972 and banned its use in the U.S. except in cases of sudden serious epidemic or infestation, when it still can be applied against disease-carrying insects. Its use is also allowed in certain areas for the protection of onions, green peppers and sweet potatoes.

DDT's demise was followed by those of other insecticides. In October 1974, the EPA halted the manufacture and restricted the sale and use of two products that are highly effective against corn pests: aldrin and dieldrin, which had also been linked to cancer in laboratory animals. Last year, for the same reason, it placed severe restrictions on the sale and use of heptachlor and chlordane, effective termite killers. The EPA has also curtailed the use of Mirex, the pesticide that is most effective against the fire ant as well as harvester and Texas leaf-cutting varieties. Tests showed that the substance is potentially carcinogenic in rats and mice and toxic to such common crustaceans as shrimp, crabs and crayfish.

Farmers are furious over the bans. "They've taken away the insecticides that really do the job," says Steve Pfister, a Lexington, Neb., corn and alfalfa farmer. But entomologists and some farm experts feel that in the long run, less dependence on pesticides will be beneficial to the farmer. Many scientists believe that the introduction of pesticides like DDT, which promised easy pest control, actually intensified the problem by encouraging the abandonment of such traditional--and sound--agricultural practices as rotating and diversifying crops and adjusting times of planting to avoid insect infestations. "Insecticides have failed not because of any inherent weakness in the concept of reducing insect populations by chemicals," writes Vincent Dethier of the University of Massachusetts in his newly published book Man's Plague? (Darwin Press; $9.95). "They have failed because of misuse, because of the unrealistic goals we set ourselves, because of irresponsibility, profit motive, laziness and ignorance."

One sign of insecticide failure is obvious. Because of overexposure, insects are becoming more immune to chemical pesticides. In fact, the Department of Agriculture reports that of the 500 or so species of insects that do significant damage to crops, 267 have built up resistance to insecticides.

As this resistance has developed, U.S. farmers have been forced to use ever greater amounts of increasingly expensive insecticides. In 1966 the U.S. used 150 million Ibs. of insecticides at a cost of $241 million. Now, the U.S. investment in insecticides is some $2.5 billion a year. But the country is receiving an ever smaller return from its investment. In California, which uses an estimated 5% of all pesticides employed worldwide, some crop losses have actually increased, in part, because pesticides frequently kill off the beneficial bugs that help keep pests under control. Prior to the introduction of insecticides, for example, spider mites were relatively insignificant pests in California. But now that spraying has killed off their natural enemies, their attacks have increased; the mites now cost the state's agricultural industry more than $116 million a year, five times what they cost 15 years ago. The rising prices of pesticides are also putting them out of reach of farmers in poor countries, such as India and the nations of Africa, where insects have been regaining lost ground.

The major result of overreliance on insecticides is what Van den Bosch calls a "pesticide treadmill," in which growers use larger amounts of pesticides each year at greater cost to achieve a degree of control. Says he: "You can't beat insects with insecticides, and we are only fooling ourselves if we think we can. They are too adaptable. They have tremendous genetic plasticity. They are prolific as hell and they are mobile. They can move if they have to."

To get off the treadmill, entomologists are advocating a different approach to pest control. They no longer speak of eradicating insect species: the costs both in dollars and environmental side effects are simply too great, the chances of success too small. What they are after instead is what George Georghiou of the University of California at Riverside calls a Mexican standoff, in which insect depredations could be kept small enough to be acceptable economically.

The strategy for achieving this goal is called integrated pest control, or ICP. Advocates of ICP leave room in their antibug arsenals for insecticides. The more potent pesticides will always be needed, they say, to cope with any insect problem that suddenly gets out of hand--a mosquito infestation brought on by an unusually hot, damp summer, for example, or an unexpected attack on a particular crop. But entomologists and agricultural scientists now believe that the most promising weapons for the battle are biological controls, which can be aimed at specific insect targets without adversely affecting either humans or the environment. Among some of the more diabolic elements of biological control:

HORMONES. Scientists are beginning to identify and mimic the hormones that regulate the growth, development and reproductive activities of insects. Zoecon Corp. of Palo Alto, Calif., has just started marketing a compound called Altosid SR-10, which is chemically similar to the juvenile hormone secreted by insects during an early stage of development. Approved for use against floodwater mosquitoes only, the compound prevents harmless juveniles from maturing into annoying adults. Mosquitoes exposed to the chemical are trapped and die in their larval or pupal stages. William Robbins, of the U.S. Department of Agriculture's research station at Beltsville, Md., is currently working on hormones that will prevent insects from molting, or shedding their outer covering, prior to passing on to the next stage of growth, and Martin Jacobson has applied for a patent for a juvenile hormone that affects house, stable and face flies, some mosquitoes and the fire ant. Taking a different approach, Entomologist William Bowers, of the New York State Agricultural Experiment Station, has isolated two substances from ageratum, a flowering plant, that interfere with an insect's production of juvenile hormones. When these antihormones are applied to immature cotton stainers and Mexican bean beetles, the insects grow into sterile adults. Colorado potato beetles treated with the chemical enter a hibernation from which they never emerge.

PHEROMONES. Insects give off and are programmed to respond to chemical compounds called pheromones. The pheromone exuded by a female insect, for example, automatically draws males of the same species for miles around. Other pheromones identify members of a colony, trigger fight or flight reactions, or are used to mark a path toward food sources. At Beltsville, Jacobson has identified the sex pheromones of the American cockroach. Oriental fruit fly, Mediterranean fruit fly and southwestern pine tip moth. Synthetic forms of such chemicals could, if spread in large quantities over an insect-infested field, so confuse male insects that they might never find females and mate with them.

In other work, scientists at the Boyce Thompson Institute for Plant Research isolated frontalin, a pheromone released by the female western pine beetle to attract other beetles when it finds a tree suitable for feeding and nesting. They also isolated verbenome, a pheromone given off by the males to stop the influx of beetles to the tree after the proper balance of males and females is achieved. After synthesizing both pheromones, the researchers applied both of them to several trees. Approaching beetles were so confused that they lost their nesting and mating instincts and dispersed into the forest. Capitalizing on the irresistible attraction of sex pheromones for specific species of insects, pest-control experts have been using the compounds to lure insects into traps, where they can be killed or counted to help entomologists determine whether further antipest activities, such as spraying with insecticides, may be necessary.

STERILIZATION. Since the females of many insect species mate only once in a lifetime, bug birth rates can be reduced by tricking them into mating with males that have been sterilized by exposure to radiation. In the 1960s, sterile males were used to eradicate the resident screwworm fly population in Florida and large areas of the Southwest. In a somewhat similar program, Agriculture Department officials in California recently released more than 350 million sterile males and females in an apparently successful attempt to control an invasion of relatively small numbers of the Mediterranean fruit fly. The invaders, mating mostly with the overwhelming numbers of sterile flies, could produce no offspring. Officials at Nairobi's ICIPE are experimenting with the sterile male technique in their war against mosquitoes and the tsetse fly. Says ICIPE founder and current director Professor Thomas R. Odhiambo: "It looks as though family planning has at last caught up with our ecosystem's co-inhabitants, the insects."

PEST-RESISTANT PLANTS. Plant geneticists have been increasing their efforts to develop plants with natural toxins or physical defenses that repel specific pests. In 1900, less than 1% of total U.S. agricultural acreage used such plants; by 1965, more than three-quarters of the overall acreage was so planted. More than 100 commonly grown food plants are now resistant to a total of 25 insect pests, but the work of developing pestproof plants must go at a rapid pace if it is to stay ahead of insect evolution. Wheat bred by man for resistance to the Hessian fly has held its own for some 30 years, even though the fly has gone through eight evolutionary changes in that period. USDA-funded scientists at Purdue University are working right now with resistant wheat strains to keep ahead of the fly's ninth change. Other researchers are also using botany to fight certain bean-eating leaf hoppers. They are developing a plant with hooked hairs on the underside of its leaves; the hairs impale soft-bodied immature hoppers as they approach for their meal.

PREDATORS AND PARASITES. The old idea of using insects to combat insects achieved a striking success in the late 1800s after a USDA official went to Australia and sent back 129 Vedalia beetles that were then released in California's citrus groves, where they ate up the cottony-cushion scale that had been damaging fruit trees. At Cornell University, Entomologists Maurice and Catherine Tauber found a tiny wasp to control the white fly, which causes serious loss to florists by attacking poinsettia plants. The wasp deposits its egg in the white fly; when the egg hatches, the white fly dies and is used for food by the newly hatched wasp. The wasps also accompany the poinsettia into the home, continuing to kill off the white flies.

Other parasites--generally the larvae of wasps or flies--are also proving effective in controlling certain insects. The spotted alfalfa aphid was brought under control by the late 1950s with the help of three Mediterranean parasites, and a total of 42 other species of insects, including the face fly that torments cattle, have since succumbed to parasites of various types. Another may soon be joining their ranks. Dr. William Nickle of the USDA at Beltsville has found a nematode, a tiny roundworm, that destroys mosquito larvae.

Even more exotic attacks are being investigated. One promising technique is the use of pathogenic, or disease-causing bacteria, to control specific insects. Entomologists have already succeeded in controlling some populations of Japanese beetle by infecting them with a bacterium that produces a fatal condition known as milky spore disease. The EPA has recently approved the use of a viral insecticide for use against the cotton bollworm and tobacco budworm.

Other approaches include the development of short-lived pesticides, which can kill insects and then break down harmlessly before they can affect other elements of the environment. Some scientists are trying to learn insect languages in an attempt to decipher them. Investigators at ICIPE are studying the pheromones termites use for communicating with each other in hopes of cracking the code and learning how to "talk termite." "When we acquire the full vocabulary of termite language, we shall be in a position to confuse or lead insects astray and therefore disrupt their social life," says ICIPE'S Gilbert Oloo. "It will be an efficient and environmentally safe mode of control."

Achieving effective, environmentally acceptable methods of insect 'control will be expensive. The cost of producing even a few ounces of a pheromone runs into thousands of dollars; the expenses involved in sterilizing insects, identifying and isolating their hormones or finding parasites or pathogens that will prey upon them are equally high. The USDA alone, for example, will spend $48 million on insect control research this year. It will be money well spent, essential for keeping the insects at bay. Even as manufacturers begin producing some of the new biological controls, there are ominous signs that the ever adaptable insect may be adjusting to man's latest weapons against them. California's Georghiou has found, in laboratory tests, that after 15 generations both houseflies and mosquitoes develop resistance to juvenile hormone insecticides.

So the battle between humans and bugs goes on, with some hope that man will continue to maintain an uneasy detente with the insect world for centuries to come. But for the long run, the odds are still heavily in favor of the insect. For, as W.J. Holland's The Moth Book poetically prophesies, it is likely that "when all cities shall have long been dead and crumbled into dust, and all life shall be on the very last verge of extinction on this globe; then, on a bit of lichen ... shall be seated a tiny insect, preening its antennae in the glow of the worn-out sun, representing the sole survival of animal life on this earth--a melancholy 'bug.' " By then, of course, man may have moved on to other worlds, friendlier solar systems. But the stowaways will have gone along.

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