by Amy Stewart
Some have accused Americans of deliberately spreading the pest: A German propaganda poster from World War II depicts red-white-and-blue-striped Colorado potato beetles advancing across a field like soldiers. The Germans believed that Americans were dropping the beetles from planes as a form of aerial agricultural warfare. They coined the term Amikäfer — a combination of the German words for “American” and “Beetle” — to describe this enemy insect. One poster reads “Halt Amikäfer,” and the other warns that the evil American beetle “threatens to destroy our harvests” and urges citizens to kampf für den frieden — fight for our peace.
This bright yellow-and-brown-striped beetle is slightly larger than a ladybug. A female potato beetle lays up to three thousand eggs in her short lifetime, usually producing three generations of beetles in a single season. Those born late in the season can comfortably survive the winter and emerge early the following year to begin the cycle again. Farmers have bombarded the beetles with an astonishing array of pesticides over the past 150 years, only to find that the insects rapidly grow resistant to the chemicals. This is due in part to their prolific reproduction rates; with three thousand offspring, one of them is bound to be born with a mutation that helps it resist a pesticide. Also, the fact that the insects feed off the leaves of nightshades, which are themselves quite toxic, suggests some level of resistance to poisons.
Meet the Relatives A member of the family commonly known as leaf beetles, which includes cucumber beetles, asparagus beetles, and other dreaded agricultural pests.
DESTRUCTIVE
THE GARDENER’S DIRTY DOZEN
They may not change the course of civilization. They might not spread the plague or send villagers fleeing for the hills. And they’ve probably never been implicated in a murder — although they do inspire murderous rages. These are just some of the pests that drive gardeners mad.
APHIDS
The presence of a few hundred greenish, soft-bodied insects glued to the underside of a leaf, all sucking away at once, is enough to give a gardener nightmares. Over forty-four hundred species have been identified in the Aphidoidea superfamily, many of them specific to a particular plant. Like body lice or ticks, they latch onto their host and start feeding, sometimes transmitting plant diseases in the process. Potato leafroll virus, one of the most serious potato diseases worldwide, is transmitted by an aphid.
But perhaps their most horrifying quality is the way in which aphids reproduce: some species are actually capable of “telescoping generations” in which one female aphid contains within her the beginnings of another youngster, which is herself already pregnant with yet another generation. These parthenogenetic insects require no males to reproduce, and they are capable of carrying on for several generations before mating with a single male.
The oleander aphid, Aphis nerii, employs a particularly devious strategy to ensure its survival. It harvests a poisonous substance called cardiac glycosides from the toxic plant and wraps the poison around its eggs to protect them from predators.
Fortunately, a variety of lady beetles, parasitic wasps, and other predatory insects will happily show up and feed on aphids if given the opportunity.
WHITEFLY
Nothing takes the joy out of owning a conservatory more than the whitefly, a despicable pest in the family Aleyrodidae frequently found in greenhouses and on houseplants. (They thrive outdoors as well, but a winter freeze will kill them off.) At only one to three millimeters in length, these tiny winged creatures are so small that they resemble a white powder sprinkled over the leaves.
Like aphids, whiteflies suck plant sap, causing leaves to turn yellow and droop. Some species also transmit disease. Simply brushing by an infested plant will release a cloud of them into the air for a moment, a sight that pains gardeners and greenhouse managers alike. Female whiteflies lay as many as four hundred eggs in their four to six week lifespan. Most greenhouses deploy a species of parasitic wasp — Encarsia formosa, which is harmless to humans — to attack them.
SLUGS AND SNAILS
These gastropods require no introduction. Gardeners who must confront them, as they slime their way across the sidewalk and into the vegetable garden, have tried some ghastly and grotesque means of defeating these enemies. From sprinkling salt on their oozing bodies, to setting out shallow bowls of beer to drown them, to picking them off plants by hand and tossing them into the street, everyone has a favored method of confronting the horror. The brown garden snail, Cornu aspersum, was introduced to the United States from France in the mid-1800s as an edible delicacy but went on to eat American gardens instead.
Gardeners on the West Coast are fortunate to have an ally in their war against snails: the lancetooth snail, Haplotrema vancouverense, is a natural predator of the garden snail. The decollate snail, Rumina decollata, has also been introduced from Europe as a predator, but gardeners can rely on a pet-safe iron phosphate bait instead.
CUTWORMS
The larvae of a number of different species of brown or tan moths, mostly in the family Noctuidae, these wormy creatures are usually found underground or hidden beneath fallen leaves, curled into a tight ball. They get their name from their habit of moving along the surface of the soil, cutting down seedlings as they emerge from the ground. Young, vigorous tomato, pepper, and corn plants can be struck down in their prime by a hungry cutworm.
Beetles, spiders, toads, and snakes will eat cutworms — although most gardeners are not desperate enough to release snakes into the garden. Cutworm collars, made from paper cups or plastic tubs and placed around young seedlings to protect them as they grow, are a favorite remedy for gardeners with just a few dozen plants to protect.
EARWIGS
While earwigs may look evil, owing to the nasty pincher-like appendages on their abdomens, these insects from the order Dermaptera aren’t really as harmful as most people believe. But they do feed on a wide variety of flowers and vegetables, from dahlias to strawberries. Anyone who has ever been confronted by an earwig while peeling apart a freshly picked artichoke knows what a nasty surprise they can be. Earwigs also dine on aphids and the eggs of other insects, making them something of a do-gooder, too. The easiest way to evict them is to set up traps of rolled newspaper or cardboard tubes, which can be emptied into soapy water in the morning.
JAPANESE BEETLES
Introduced by accident in a New Jersey nursery in 1916, Popillia japonica is feared and loathed in the eastern United States. The bronze and green iridescent beetles feed on about three hundred different plants, working collectively to devour them from the top down. Leaves are often left with nothing but the veins, resulting in a lacy pattern that would be elegant if it weren’t so destructive. The larvae destroy grass by chewing through the roots, making them a pest of parks, lawns, and golf courses. Americans spend $460 million per year trying to control Japanese beetles and repair the damage they inflict. This process can be difficult and frustrating, usually requiring some combination of picking them off by hand, releasing predatory insects, setting up traps, and replacing plants with varieties that these voracious pests don’t eat.
One plant is fighting back: scientists at the U.S. Department of Agriculture have discovered that geraniums (Pelargonium zonale) produce a substance that paralyzes the beetles for up to twenty-four hours — enough time for a predator to attack.
CUCUMBER BEETLE
Don’t be fooled by these cute spotted and striped beetles. They may resemble yellow or green versions of ladybugs, but they are nowhere near as well loved. The spotted cucumber beetle, a member of the Diabrotica genus, and the striped cucumber beetle of the genus Acalymma, dine on squash, melons, cucumbers, corn, and other kitchen garden favorites, sometimes transmitting diseases that bring on bacterial wilt and cucumber mosaic virus. Some gardeners cover their young crops with floating row covers to keep them away.
TOMATO HORNWORM
Confronting a four-inch-long-green caterpillar can be a daunting task. These caterpillars (Manduca quinquemaculat
a, the tomato hornworm, and Manduca sexta, the tobacco hornworm) can decimate most plants in the nightshade family — including tomatoes, eggplant, and tobacco — during the month or so they spend as caterpillars. Once they pupate, they emerge as surprisingly large, beautiful sphinx moths that resemble hummingbirds.
As adults they feed on flower nectar, and the sight of them visiting evening-blooming flowers can be quite enchanting. (The caterpillars of some sphinx moths feed on trees and shrubs, not tomatoes, so the presence of a hummingbird-like moth in the garden does not necessary signal a hornworm infestation in the tomato patch.) Because they are so large and easy to spot, gardeners often handpick the caterpillars — but if they seem to have tiny white cocoons attached to them, they should be left alone. This means parasitic wasps have already come to the rescue.
FLEA BEETLE
These tiny creatures get their name from their habit of jumping when disturbed. Members of the leaf beetle family (Chrysomelidae), they chew tiny “shothole” bites in leaves that resemble scattered gunshot. Some species will also chew pits into beets, melons, and other crops. Most plants will outgrow them, though some farmers use trap crops like radishes to lure them away, or they suck them up with a bug vacuum.
CODDLING MOTH
The larva of this moth is the proverbial worm in the apple. It chews tunnels into not just apples but also pears, crab apples, peaches, and apricots, making it one of the most despised fruit tree pests. A number of birds and wasps prey upon coddling moth larvae, but this often isn’t enough. Backyard orchardists pull off infested fruit early in the season and set traps baited with pheromones, but if any tree in the neighborhood is unprotected, it serves as a perpetual breeding ground for the moth.
One effective but time-consuming method is to staple a bag around each fruit (called “Japanese apple bags” in the trade) to keep the bugs out — but this means putting up with the rather odd sight of a tree covered in bags all summer long.
One of the more satisfying home remedies is to point a torch at the tree and set infested areas aflame, but experts advise against this.
SCALE
These dreadful sucking insects in the superfamily Coccoidea latch onto a tree and surround themselves with a protective waxy covering so that they resemble a tick. Like aphids, they excrete a sweet sticky substance called honeydew, which in turn encourages the growth of black sooty mold. Their protective shells make them impervious to most forms of control, but it can be quite satisfying to scrape them off a branch with a dull knife. Winter sprays of horticultural oils keep them in check, as do some parasitic wasps.
TENT CATERPILLAR
Few sights are more appalling than that of dozens of fuzzy caterpillars massed around a branch, surrounded by their characteristic silky “tent” that resembles a dense spider web. The caterpillars, members of the genus Malacosoma, can strip a tree bare in a bad year. (In other years they are hardly seen at all; they tend to go through boom-and-bust cycles.) One of the more satisfying home remedies is to point a torch at the tree and set infested areas aflame, but experts advise against this for safety reasons and on the grounds that the fire does more damage to the tree than the caterpillars would. Instead, the tents can be cut off and crushed or wrapped in a plastic bag and thrown away.
DESTRUCTIVE
Corn Rootworm
DIABROTICA VIRGIFERA VIRGIFERA AND D. BARBERI
Corn faces any number of devastating pests, from the European corn borer to the corn flea beetle to the earworm. They cause billions of dollars in crop loss every year, not to mention the expense and hazards involved with controlling them. But one has proven to be more devious than others at outwitting farmers: the corn rootworm.
SIZE:
6.5 mm
FAMILY:
Chrysomelidae
HABITAT:
Found in close proximity to corn and a few species of wild grasses
DISTRIBUTION:
Mexico, United States, and Europe
Despite its name, the corn rootworm is no worm; it is actually a small beetle not much bigger than a ladybug. During the larval stage, when the creatures live underground and feed on the roots of corn plants, they do resemble tiny white worms — but they emerge in spring as elongated brown or green beetles.
Several species have plagued American farmers for decades, including the western corn rootworm, Diabrotica virgifera virgifera, and the northern corn rootworm, D. barberi. Both of them probably originated in Mexico and worked their way into what is now the United States as Native Americans began planting corn as a crop. Understanding their life cycle was the first step in fighting them.
In late summer, female rootworms lay eggs underground in the roots of cornstalks. Those eggs hibernate through the winter, and when spring begins to warm the soil, they hatch as tiny larvae that must feed on the roots of a corn plant to survive. Because corn is an annual plant, this survival strategy depends on a farmer seeding in a new crop every year. The larvae continue to feed through the summer, and then pupate in the soil, emerging as full-grown beetles just as the corn is starting to ripen on the stalk. The adults eat corn pollen and silks, then mate and lay eggs underground before they die.
The northern corn rootworm figured out how to outsmart the farmers.
For a while, farmers used pesticides to kill the insects, but they eventually grew resistant to the chemicals. Crop rotation proved to be the best strategy for breaking the rootworm’s life cycle. Because the larvae could not eat any plant other than corn, rotating corn with soybeans would stop them in their tracks. With only the roots of soybeans to eat, the larvae would die off without ever maturing or mating. That would make it safe to plant corn in the field the following year.
This method worked well for decades, allowing farmers to use fewer pesticides and improve the health of the soil. But in the eighties and nineties, everything changed.
The northern corn rootworm figured out how to outsmart the farmers. It evolved to stretch its winter hibernation over two seasons, effectively realizing that the farmer would plant inedible soybeans for a year but would then return with tasty corn in two years. By laying eggs that could remain dormant through an entire year of soybean planting, and then hatch a year later when the corn returned, it was able to outlast the tried-and-true crop rotation and once again become a serious pest of corn farmers. This adaptation is called “extended diapause.”
To the amazement of entomologists, the western corn root-worm developed a different way to survive that was just as ingenious as its northern counterpart. Rather than sleep through the soybean rotation, it adapted by laying eggs whose larvae didn’t mind eating soybeans. Now that this so-called soybean variant is immune to the practice of crop rotation as well, farmers are once again looking for a solution. New generations of pesticides, as well as genetically modified corn varieties that the rootworms can’t eat, may look promising in the short term, but the rootworms have proven that they can outrun such efforts. As one crop scientist said: “It’s another magic bullet. We’ve fired them before . . . in agriculture, problems are not solved forever.”
Meet the Relatives Corn rootworms are a type of leaf beetle and are related to the asparagus beetle, the Colorado potato beetle, and a number of other destructive beetles.
DESTRUCTIVE
Death-watch Beetle
XESTOBIUM RUFOVILLOSUM
Now, I say, there came to my ears a low, dull, quick sound, such as a watch makes when enveloped in cotton. I knew that sound well, too. It was the beating of the old man’s heart.”
SIZE:
7 mm
FAMILY:
Anobiidae
HABITAT:
Decaying wood in forests, or the timbers of old buildings
DISTRIBUTION:
This particular species is found England; its relatives are scattered across Europe, North America, and Australia.
So says the madman who narrates Edgar Allan Poe’s frightful story “The Tell-Tale Heart.” He describes his victim groanin
g in the night as he hears the approach of death. And what was the sound that kept the old man — and his murderer — awake at night? “He was still sitting up in the bed listening; just as I have done, night after night, hearkening to the death watches in the wall.”
The death-watch beetle to which Poe referred is a bug that sits in the rafters of old homes, quietly munching away at the beams and calling to its mate with the soft tick-tick sound it makes by tapping its head against the wood.
Francis Grose, in his 1790 book A Provincial Glossary; with a Collection of Local Proverbs, and Popular Superstitions, included the beetle in his list of “Omens Portending Death.” The list begins with such omens as the howling of a dog, a lump of coal in the shape of a coffin, and a child who does not cry when sprinkled in baptismal water. The beetle was another sign that the end was near: “The ticking of a death-watch is an omen of the death of someone in the house wherein it is heard.”
“Next the ghastly ticking of a deathwatch in the wall at the bed’s head made Tom shudder — it meant that somebody’s days were numbered.”
This old superstition persisted. Consider Tom Sawyer’s long night waiting for Huck Finn to come and take him to the graveyard: “By and by, out of the stillness, little, scarcely perceptible noises began to emphasize themselves. The ticking of the clock began to bring itself into notice. Old beams began to crack mysteriously. The stairs creaked faintly. Evidently spirits were abroad. A measured, muffled snore issued from Aunt Polly’s chamber. And now the tiresome chirping of a cricket that no human ingenuity could locate, began. Next the ghastly ticking of a deathwatch in the wall at the bed’s head made Tom shudder — it meant that somebody’s days were numbered.”