Man Vs. Insect
INSECTS LOVE US. TERMITES ARE CONNOISSEURS OF THE wood we use in construction, each year munching through $3 billion worth. Fleas, ticks (which are not insects, strictly speaking), biting flies, and disease-vectoring mosquitoes are blood-loving little vampires in search of warm, carbon dioxide-exhaling bodies to dine on. Housefleases they transmit is big Every year more than a billion pounds of pesticide, with active ingredients worth $8.5 billion, changes hands in the United States. New York City alone spends more than $100 million annually just combating ants. America, the nation of consumer choice, has 20,000 household pesticide products to choose from, including bug bombs, bait boxes, liquids, granules, dusts, aerosols, and sticky strips. The average American family keeps a home arsenal of three or four pest-control products, and restaurants in the $400 billion U.S. food industry remain on heightened alert against vermin like cockroaches and the always irritating fly in the soup.
Despite this massive pest-control blitz and the harshest modern chemical warfare, the enemy has suffered only temporary setbacks and continues to counterattack. More than 500 insect species, from malarious mosquitoes to houseflies and farm pests, in 168 countries are resistant to insecticides ranging from the old organochlorine compounds, like DDT and chlordane, to organophosphates, carbamates, and the latest natural products derived from plants and microbes. In Illinois and Indiana, the Western corn rootworm has recently fought back against a traditional nonchemical remedy, corn/soybean crop rotation, by acquiring a taste for soybeans. This amazing adaptability and talent for overcoming adversity has served insects well, allowing them to survive major global climate changes and outlive the dinosaurs.
That’s one reason people keep falling back on a conceptually very simple—yet vexingly difficult—solution: trapping insects. Trapping is often used, with varying success, for short-term pest relief in small areas like farm fields, yards, rooms, and buildings. One of the rare large-scale implementations of trapping took place in China in the 1970s, when millions of blacklight traps blanketed whole rural provinces for agricultural pest control. Insects trapped in pails of water beneath the lights became fodder for fish farming, but the system was not sophisticated enough to avoid trapping beneficial insects along with the pests.
Trapping is at its best, however, and provides better longterm relief, when integrated with other pest-control technologies like pheromones, attractants, sanitation, and pest-fighting beneficial insects. Traps are also useful for detecting infestations of such insects as underground termites, and in these days of greater environmental awareness, traps can form part of a larger insect-management effort that uses small amounts of chemicals but targets them precisely.
Medieval Europeans associated pest outbreaks with superstitions and divine punishment for sins and pursued everything from magical rituals to legal and religious proceedings in their attempts to get rid of troublesome insects. Cutworms, for example, were excommunicated in Bern in 1476, and caterpillars were banished by the vicar of Venice in 1485. Neither method proved effective. It was not until 1668 that the Italian physician Francesco Redi demonstrated, using scientific experiments with sealed and open food flasks, that winged adult flies laid eggs that hatched into maggots. In the early 1700s, spurred on by the realization that insects had life cycles and could be studied and controlled, the German physician Franz Ernst Br’fcckmann began building flea traps and flytraps to protect public health.
Rodent trapping was commonplace in medieval Europe, but ancient insect control had hit a plateau in 200 B.C. , when sticky bands made of oil and bitumen trapped bugs pestering the Roman Empire. The Romans also mixed arsenic or hellebore with milk or wine to make poisonous fly baits. Then insect control and Roman notions of sanitation slipped into the Dark Ages, and flea-borne bubonic plague, the Black Death, killed 30 to 50 percent of Europe’s population after its emergence in 1348 and remained a periodic scourge for centuries.
Brückmann’s devices were the first flea traps in human history, and a flea-bitten European aristocracy flocked to them in a big way. Worn around the neck like haute couture pendants, the flea traps were exquisitely crafted perforated cylinders made of ivory or silver. A rod inside the trap was smeared with blood or a sticky honey bait. Fleas entered through small holes to get the bait and were trapped inside. One version came equipped with a small microscope, “to examine the captured enemy,” according to the German entomologist Bernhard Klausnitzer, who saw a flea trap from Cologne engraved with the motto “Revenge is sweet.”
Brückmann also built a flytrap; it was equally serious in its public health purpose but also more like a clever toy. He described it as “a wooden machine, or oblong, rectangular box,” containing a sweetly scented honey or syrup bait. The trap was placed in a room buzzing with flies, and “when a goodly crowd has assembled” inside the trap, a slight pressure from the finger activated a spring, snapping the lid shut and trapping the flies inside.
“If such a box is now held to the ear,” Br’fcckmann wrote in his 1735 booklet The Newly Invented and Curious Fly Trap , “it is impossible for any pen to describe what a lamentable concert is to be heard, composed of all kinds of humming, buzzing, singing, sounding voices, with a complete lack of harmony, enough to afflict the ear. Anyone wanting to play the tragedy to the end and cause a veritable bloodbath, need only apply firm pressure several times to the extended rod which drives home the attached square of wood, thus squashing and killing all the flies…. If one repeats this process several times in a house or room which is alive with flies and midges, the house will soon be clear of them.”
The inventor suggested that “it would be a good thing if … landlords were obliged by a firm statutory regulation to acquire such a fly trap” for inns and taverns, which he described as “often thoroughly incrusted with fly droppings.” There is no evidence that he got his wish, but he would no doubt have been a happy traveler if he could have seen the hidden cockroach traps, ant baits, and fly-snagging light traps that protect many restaurants today. Though their origins were long ago forgotten, Br’fcckmann’s insect-trapping ideas eventually traveled across the ocean to a fly-plagued U.S.A., where mechanical flytrap designs were patented as early as 1851.
“In the horse and buggy days a small or large fly trap was a common gadget in the home, barn or store,” wrote the Ohio entomologist Alvah Peterson in 1934. Until automobiles came along, the manure from thousands of horse-drawn streetcars and carriages bathed big American cities in a sea of flies. Rural America’s millions of poultry, cattle, and pigs added more manure and flies. One pound of manure can serve as a nursery for 400 flies in four days, and one cattle-size animal’s droppings can theoretically produce four million flies annually. Thus, even the cleanest-swept streets in the 1800s and early 1900s had enough animal waste, not to mention garbage and other organic debris, to keep homes and businesses buzzing.
American industry, like its nineteenth-century European counterpart, produced an array of poisons, screens, netting, curtains, fans, flypaper, and traps to keep nuisance flies within tolerable limits. Chairs with bicycle pedals powering fans to shoo off flies were the equivalents after the Civil War of today’s Exercycles. Honey-baited lantern- or chimney-style flytraps bolted to buildings were a common sight in the Mississippi River area and the urban South.
Baited flytraps are mostly variations on an inverted screenedcone design that has changed little in more than a century. The design takes advantage of the strong tendency among adult flies to be attracted to light. This behavior is also exploited by light-trap manufacturers, who are moving from bug-zapping electrocution grids (which date from 1927) to old-fashioned sticky trapping surfaces. Light traps are also becoming more design-conscious for restaurants and retail outlets, giving patrons the illusion that they’re viewing decorative light fixtures.
“You can work a fly from room to room by turning on lights in one room and darkening lights in other rooms,” says Jerry Hogsette, a U.S. Department of Agriculture entomologist. “But the bugs do change very quickly.” Hogsette is now encountering flies so well adapted to dark, wet poultry-house environments that they refuse to fly into light.
Nonetheless, the average nuisance fly is still easily outwitted by the old-fashioned baited cone. The record single-day catch from an inverted-cone flytrap is 129,000 flies, and the all-time single-season record catch from one is 8,337 gallons of flies in 1930s Texas. Thé basic design, which requires regular replacement of baits and cleaning out of dead flies, is still a variation on what Alvah Peterson described in 1934:
“It usually consisted of an all screen cylinder [covered at the top and open at the bottom] with metal supports and mounted on short legs. On the inside a screen cone was attached to the lower metal ring. This extended upwards at least half way toward the top and terminated in a small opening not over one inch in diameter. Baits attractive to flies were placed in a dish below the center of the screen cone… . When the adult flies were fully fed they flew upwards toward the light and came to rest on the inner portion of the cone. From this point they crawled upward and entered the cage through the hole in the top of the cone. Once within the cage they assembled on the outer wall where they lived and died. So far as is known no fly ever reversed its course and escaped from the cage through the hole in the cone. This type of cage is just as effective today as it was 50 years ago.”
Another time-honored favorite is the walk-through flytrap, which is like a dry car wash that removes flies from cattle. The basic idea is that cattle walk in at one end with flies on their skin and leave at the other end without them. The target is the tenacious, blood-sucking horn fly, which irritatingly lodges itself where cattle cannot remove it with their mouths or tail swishing. One of the earliest patented walk-through flytraps was designed by Robert H. Guthrie, a Canadian farmer. His 1893 barnlike enclosure had brushes mounted on the inside. Flies were shuttled Rube Goldberg-style from cattle to brushes to netting to cages for destruction in furnaces. A variety of walk-through sheds, houses, and tunnel-like enclosures with varied means of catching and destroying flies were patented over the next century.
WITH HORN-FLY COSTS APPROACHING A BILLION DOL lars a year in the United States alone, walk-through flytraps attracted a renewed burst of inventive energy in the 1980s and 1990s. Robert Tozer and Robert Sutherst, of Australia, brought their new designs to the United States and collaborated with university and USDA inventors like Larry Pickens, who had achieved renown in the insect world for his solar-powered, electrically shocking, housefly-zapping pyramid solar traps. The state of the art in walk-through traps has a solar-power option and an interior equipped to brush off and zap cattle flies. Exterior colors and lighted grids attract and kill the flies that hop off outside the trap (mostly lightloving flies that avoid entering darkened areas) to wait for exiting cattle.
Flypaper, a variation on the ancient Roman sticky bands, was manufactured in America before the Civil War by Samuel Wightman of Philadelphia. Many people also had their own recipes and made flypaper at home, coating paper with, for instance, a blend of one part molasses and six parts bird lime. Others went to local druggists, who custom-coated paper with adhesive on demand. Today the Tanglefoot Company, of Grand Rapids, Michigan, maker of adhesive pest-management products, traces its origins to the manufacture of flypaper in the 1880s by the O & W Thum Company.
“Sticky fly-paper, as ordinarily manufactured,” Otto Thum wrote in an 1883 patent, “consists of a sheet of sized [i.e., treated with a starchy surface coating] paper coated with an adhesive mixture of resin and castor-oil, a margin being left uncoated for convenience in separating the sheets,” which were boxed in lots of 25 to 100. The messy, often runny adhesive layer limited flypaper manufacture to small batches and localarea sales. Otto Thum changed the industry and addressed this issue in his patent:
“My invention relates to an improved method of making and packing sticky fly-paper; and its object is to prevent the running and spreading of the adhesive coating under any circumstances, so that large quantities of the paper may be packed and transported without deterioration and kept on hand. The invention consists in surrounding the adhesive coating with material of such a nature that it will adhere slightly to an adjoining sheet, but will separate readily for use, and when the sheets are in contact will prevent the adhesive coating from spreading.” Thum did not specify exactly what that material might be.
Whatever it was, its longer shelf life enabled Grand Rapids to become a world center for flypaper manufacture and to export this previously delicate article as far as Russia, Europe, and Africa. But today the once-popular Tanglefoot brand and its distinctive in-store displays are little more than a 1918 caselaw footnote often cited in trademark-infringement cases. Flypaper went the way of the blacksmith as America motorized and manure disappeared from city streets. Then the Nobel Prizewinning discovery of DDT’s killing powers, by Paul Hermann M’fcller, a J. R. Geigy Dye-Factory Company chemist in Switzerland just before World War II, ushered in an era of reliance on synthetic pesticides. With broad-spectrum insecticides like DDT and chlordane, life became easier (at least until resistance developed) because one product worked against most insects.
HOWEVER, INSECT-TRAPPING ADHESIVES NEVER COM pletely disappeared under the pesticide onslaught. Even today the USDA’s Forest Service and others routinely use adhesives like Tree Tanglefoot by the gallon in ways the ancient Romans would have recognized—for example, attaching sticky bands to tree trunks to trap gypsy moth caterpillars. Adhesives also coat tens of millions of disposable cardboard, wood, and plastic traps, capturing uncounted billions of beetles, cockroaches, moths, flies, and other insects every year. In the war against biting flies, adhesive substances from various manufacturers have coated black roofing shingles, brown boards, Plexiglas squares, plywood pyramids, fiberglass panels, colored boxes, cow silhouettes, cylinders, brightly colored helium-filled balloons, ribbons, tape, white buckets on poles, and blue plastic cups mounted on cars or worn beanie-like atop heads.
To be successful, trapping requires studying the biology and ecology of each targeted pest species to learn its preferences (optimum trap size, shape, humidity, temperature, texture, color, placement, bait, sex pheromone blend). This means employing entomologists to conduct the insect equivalent of focus groups.
Insect preferences are teased out through various means. For example, in an electroantennogram, insect antennae are excised and wired to equipment measuring neural responses to airborne puffs of pheromones and plant aromas. Servospheres are incandescent globes with computerized motors that keep insects walking in place while recording body movements in response to precise quantities of scent molecules. Clear plastic tubes with odors flowing downwind are used as wind tunnels to test insects’ upwind flight responses. Insects can also be placed at the stem end of a Y-shaped glass tube and given a choice between two odors. Elaborate choice arenas with multiple compartments offer insects simultaneous choices among several different substances. Cameras can capture insect behaviors such as movements or antenna cleaning for computer software to quantify in the search for the best trap baits, attractants, and pheromone blends.
In 1959 the German chemist Adolph Butenandt completed nearly three decades of research, which included grinding up half a million female silkworm moths, to discover the first sex pheromone ever identified, bombykol. Since then more than 1,500 insect sex pheromones with potential trapping and mating disruption uses have been discovered (as well as animal and human ones). In her 1962 book Silent Spring , Rachel Carson hailed pheromones as “an experiment in psychological warfare” because synthetic female sex pheromones fooled male insects into mating with inanimate pheromone-impregnated objects.
Pheromones for thousands of different insects from flies to codling moths are formulated into lures. Every year millions of these are placed into disposable adhesive-coated cardboard traps or plastic traps like those sold in supermarkets and hardware stores for cockroach control. Thousands of new trapping possibilities are arising as researchers investigate plant aromas, essential oils, food baits, and various other natural and synthetic insect attractants and repellents.
Since at least 1922, carbon dioxide from dry ice has been used as a mosquito bait, mostly by entomologists doing trapping surveys or research. (Target species sense carbon dioxide and moisture and think they come from exhaled animal or human breath.) What’s new in recent years is the almost bewildering array of mosquito and biting-fly traps being marketed to homeowners at several hundred dollars apiece. Despite arguments that there are better mosquito traps on the market, the Sonic Web has vector-control specialists excited. The best SonicWeb models combine the lure of carbon dioxide, moisture, warmth (body heat), other fly attractants (octenol, along with light on some models), heartbeat sounds, and sticky flypaper.
Working with Tracey Tarn, a graduate student, the USDA entomologist Jerry Hogsette has found that traps with inaudible, low-frequency sounds that suggest blood pulsing could form a barrier stopping 90 percent of stable flies from reaching horses. The original SonicWeb inventors combined “Radio Shack stuff” like automobile speakers and computer chips with PVC tubes, says Hogsette. Now he’s toying with the idea of adding a dial to customize the heartbeat sounds to match those of cattle, horses, dogs, and humans.
Integrating disparate attractors like scents, sounds, shapes, and colors is a challenge for trap designers. For example, without carbon dioxide, SonicWeb is much less effective against mosquitoes. White plastic traps with heartbeat sounds capture horseflies, but black plastic traps with heartbeat sounds do not. Red spheres are best for trapping apple maggot flies (an attractant apple odor and pesticide may also be added). White sticky traps snare the tarnished plant bug, whose feeding gives strawberries the puffy, disfigured look known as catfacing. Blue cardboard sticky strips and adhesive-covered blue plastic cups are best for capturing thrips. Orange or yellow sticky strips snag adult carrot rust flies before they lay eggs that will hatch into root-ruining maggots. But the most promising development of all may be integrated pest management, an approach that eschews preventive pesticide use and relegates spraying to a last resort when all else has failed. The key to IPM is monitoring insect populations to indicate imminent damage.
In the mid-twentieth century, saturating soils with a barrier of a long-lasting chemical like chlordane was the top choice for protecting real estate from subterranean termites. Then in the late 1980s the U.S. Environmental Protection Agency banned chlordane, leaving only a less long-lasting chemical, chlorpyrifos (Dursban), for soil termite barriers. Dow Chemical was marketing heavy volumes of Dursban and had an 80 percent market share for soil termite barriers in the absence of competition from chlordane. But by the late 1980s heavy soil applications of Dursban were causing their own pollution and costly litigation headaches.
IN 1988 NAN-YAO SU WAS HIRED BY THE UNIVERSITY OF Florida to come up with a weapon against the Formosan subterranean termite, a pest that had hitchhiked to the United States on ships from the South Pacific during World War II. Formosan termites were spreading rapidly through the South and causing devastating damage in some areas, particularly New Orleans’s famous French Quarter. Florida feared that its new housing tracts would soon become termite fodder. Indeed, subterranean termites of various sorts were beginning a continentwide orgy, munching on older neighborhoods as far north as Toronto and threatening to undermine the White House and the Statue of Liberty.
As a graduate student at the University of Hawaii in the late 1970s and early 1980s, Su was already formulating the trapping and baiting ideas and the IPM approach that he would later persuade Dow Chemical to adopt in lieu of heavy volumes of soil termiticides. “It was very clear to me that the traditional chlordane soil barrier was a myth,” said Su.
As early as 1930 a man named E. M. Ehrhorn had written an article criticizing soil barriers because they did not kill the termite colony. In the case of subterraneans, as the University of Hawaii professor Minoru Tamashiro and his graduate students in more recent decades learned, this could include castes of several million workers and soldiers (termites have antlike social arrangements) spread out over acres. But chlordane worked better as a soil barrier than anything else before it, and people had tried arsenic, kerosene, and everything else they could think of. Moreover, chlordane was cheap, so everybody used it until it was banned. Dow no doubt sensed that Dursban could suffer the same regulatory fate as chlordane, and it assigned some creative thinkers to consider an eventual replacement.
Su was heavily influenced by Tamashiro, whom those in the termite world consider the godfather of all the termite-trapping systems now being used. One example is Dow’s Sentricon, a stand-alone trapping and baiting system to protect real estate, which Su invented and patented for the University of Florida and Dow later improved. Sentricon now protects more than a million structures nationwide. Half a dozen similar systems are on the market, but all are basically variations on the baits and traps written up in an August 1973 article in Environmental Entomology by Tamashiro, Jack Fujii, and Po-Yung Li.
Like many insect traps that have found their way into commerce, Tamashiro’s was developed for research purposes, as the title of his article reflects: “A Simple Method to Observe, Trap, and Prepare Large Numbers of Subterranean Termites for Laboratory and Field Experiments. ” Another former Tamashiro graduate student, Ken Grace, now chairman of the entomology department at the University of Hawaii, took the trapping ideas to the University of Toronto, where Tim Myles added his own wizardry, known as trap-treat-release.
Myles takes the IPM admonition to minimize pesticide use to its extreme and views termite control as an area-wide activity for the whole neighborhood. (In New Orleans the Mosquito and Termite Board knows that traps are needed for the entire French Quarter, for termites are communal animals with no respect for common walls and property boundaries.) Myles baits his traps with corrugated cardboard, a termite favorite, because they love its little tunnels. When termites find the bait, as happens pretty quickly in many Toronto neighborhoods, Myles takes the roll of cardboard teeming with thousands of termites back to the lab. Eventually he gets trays full of pure, clean termites and hand-daubs them with minute amounts of a slow-acting pesticide. The termites are then brought back to the place they were captured, where they spread the pesticide to the entire colony.
Sentricon takes a slightly different tack, using wood in traps that monitor for termites. When termites find the wood, which may take a couple of months even if a colony is nearby, then and only then are tiny quantities of a slow-acting poison added for them to take back to their nests. An advantage of having pure wood without the pesticide for monitoring is that if someone decides to blame their ills on the presence of the trap, the judge will throw out the case. And in contrast with treating soils with hundreds of gallons of insecticide, little of which makes it to the termite nest, traps use only a fraction of an ounce of insecticide, and it is perfectly targeted by the termites themselves. (Wood used in new construction is sometimes impregnated with insecticide, but this creates its own problems with cost, waste disposal, and toxicity to humans and animals.)
The trapping story does not end there. Dr. Su is working on electronic printed circuits to embed in the wood so that the trap can be monitored without being opened. Eventually traps will be hooked into a wireless network, and someone watching over the Internet will be able to see when a termite has broken the circuit and a toxicant needs to be added to the bait. In the future, biological controls, including termites’ natural enemies or even their own gut microbes, may be part of the bait mix. But despite all the technology that has been applied through the ages, insects always seem to find a way to adapt to whatever we throw at them. No one is predicting that this will be the final chapter in the struggle between humans and insects.