The Big Ratchet: How Humanity Thrives in the Face of Natural Crisis (22 page)

The locusts came again in 1877. And then they vanished, mysteriously, and have not come back to plague North American farmers since. Entomologists speculated about the reasons for the disappearance. Perhaps the loss of the nearly extinct bison herds or the extinguished fires that Native Americans had routinely used to burn the prairie had somehow
altered the locusts’ habitat. Or maybe the locusts couldn’t live on the alfalfa that had spread across the plains. More than a century later, an ecologist at the University of Wyoming, Jeffrey Lockwood, reopened the puzzling case of the vanished
Rocky Mountain locust. His explanation—a quirky accident.

In the 1880s, as pioneers were expanding across the frontier, the farmers put their fields precisely in locations that coincided with the locust breeding grounds. Some of those places were the river valleys of Montana and Wyoming, where locusts buried their eggs in the ground next to streams between swarms. These were the same places where farmers found fertile soils and ready sources of water near streambeds to plant their crops. Plows pushed some of the locust eggs down into the soil so they could not hatch. Birds ate those eggs that the plows churned to the surface. Irrigation drowned the eggs and the young locusts that managed to survive. There was no way for the locusts to reproduce. That brought an end to the Rocky Mountain locust. The last live specimen was found on the Canadian prairie in 1902. “The most spectacular ‘success’ in the history of economic entomology—the only complete elimination of an agricultural pest species—was a complete accident,”
Lockwood concluded. It’s hard to say what the course of the massive expansion of North American agriculture in the late 1800s would have been if not for the demise of the Rocky Mountain locust.

Locusts are a particularly virulent and destructive pest for the world’s food supply, but they are only some of the many hundreds of species that wreak havoc on farmers’ fields. Weeds compete with crops for water and nutrients; bacteria and fungi produce mold and rot; aphids and weevils, among scores of other insects, are just a few of the other pests that feed off of fields around the world, along with birds, rabbits, rodents, deer, elephants, and more. Even with today’s barrage of pesticides and other defenses, worldwide pests and plant diseases destroy nearly three out of every ten tons of crops before the harvest,
and another one in every
ten tons afterward. There are no two ways about it. It’s a raging battle, farmer against pest.

And in a strange twist, humanity’s progress in growing more food has aided the enemy. Recall the fungus that set off the Great Irish Famine in the mid-1840s. Potato plants grown from sprouts were genetic clones, and the fields were close together. The fungus took advantage of the situation, with devastating results. It was the same for the American corn blight of the 1970s. The biggest difference—and the irony—was that farmers of the 1970s could trace the corn rotting in the fields directly to plant breeders’ efforts to produce uniformly high-yielding crops.

On April 18, 1971, the
New York Times
described the situation in an article headlined “Corn Blight: A
Triumph of Genetics Threatens Disaster,” linking hybrid corn’s success directly to its undoing. The key was the plant breeder’s trick to eliminate corn’s ability to self-fertilize. The old way was to pull off tassels from the top of each corn plant by hand, a laborious and expensive process. Breeders had developed a variety named T-cytoplasm that made the pollen sterile to guard against self-fertilization. With this type of corn, there was no need to perform the detasseling operation. But the variety had a fatal flaw, which had been discovered in the Philippines a decade earlier. It was highly susceptible to a fungus that caused leaf lesions, decayed ears, infected kernels, and rotted stalks. American farmers didn’t pay much attention to the warning, and by January 1970, the disease had taken hold in Florida. A wet spring that year helped the fungus spread into the southern United States and across the Corn Belt in southern Illinois and Indiana. The fungus now had the farmer’s attention. Unfortunately, it was too late to remedy the problem with fungicidal sprays.

The corn crop suffered widespread damage, and the amount of food lost was many times greater than what had been lost to the Irish potato blight. Fortunately, the cost in terms of starvation and emigration
was far less, as corn was only one of many crops in the country and people’s diets were more diverse. But the lesson was clear. Large fields of genetically similar crops—monocultures—are invitations to pests, allowing the pests to spread without hindrance once they find suitable hosts. Farmers did not plant the T-cytoplasm variety the following year, and thousands of teenagers once again found summer employment pulling tassels from cornstalks.

Problems with monocultures are not limited to human farmers. Leaf-cutter ants also have little genetic variation in their fields. In their case, parasites attack their monoculture mushroom gardens despite the farming ant colony’s efforts to weed out alien spores. Like human farmers, ants rely on pesticides, but their pesticide consists of bacteria growing on their own bodies, which kill harmful parasitic fungi. When the ants secrete the soil bacteria, a natural enemy of the harmful fungus gets into the
gardens to kill off the pests. (In fact, it’s the same bacteria that the pharmaceutical industry uses to make antibiotics.)

Pests will always try to pilfer the food that people or leaf-cutter ants produce. After all, the bacteria, fungi, insects, and other animals we consider pests are trying to eat and stay alive as best they can, just like we are doing. Chemical fertilizers, machinery, and modern irrigation enabled the spread of monocultures throughout the industrialized world and in parts of the developing world. But the monocultures created feasts for pests, which set in motion quests for even more powerful means to rid the fields of the annoying nuisances.

Humanity has added to the pest burden not just by creating easy targets in monocultures, but also by making it so convenient for pests to spread to new places. As people move around the world, other plants and animals go with them. Many common foods have spread along this route: corn and cassava from the Americas, for example, are now African staples. Other, less desirable species sneak in surreptitiously in ship containers, packing material, airplane hulls, and tourists’ luggage.
Whether by accident or not, they end up in places where they have no natural predators to hold them in check. Without the long coevolutionary process to balance predator and prey, newly introduced species can run rampant and even crowd out native species.

Among these invaders are the cassava mealybug and the green spider mite. The mealybug and the spider mite accidentally made their way from their native South America, where they are only minor pests, to Africa in the early 1970s. With no natural predators, they devastated crops of the staple food consumed
throughout tropical Africa. A similar story applies to the Russian wheat aphid, which accidentally moved into the Great Plains in the mid-1980s, causing millions of dollars in
damages to the wheat crop, and to the Mediterranean fruit fly, which traveled on imported fruit from its native sub-Saharan Africa, first to Hawaii and then to the continental
United States in the early 1900s. Likewise, the Hessian fly hitchhiked on a ship from England to New York during the American Revolution. The devastation on farms around the city was so profound that entire wheat fields were ravaged within a few days. George Morgan, a New Jersey gentleman farmer and colonel in the Revolution, named the insect to demonstrate disdain for both the pest and the German mercenary soldiers who were fighting for the British. The Hessian fly pesters
wheat farmers to this day. The list goes on of troublesome species that have slipped in to new places with trade and the movement of goods around the world. An interconnected world means a never-ending need to keep invasive
species under control.

Scarecrows to Strychnine

Agriculture, and particularly stowaway species and genetically uniform monocultures, lock humanity into finding ways to overcome pests. Well before the pesticide bonanza of the past century, humans were adept
at using their ingenuity to devise tricks to keep as much of the bounty for people and not pests. The ancient Egyptians had a clever strategy. During the season when the wheat was ripening, they hid in the rushes next to their fields. As the quail descended in hopes of a meal, the farmers jumped out, spread a net over the field, and made loud noises so the quail would attempt to fly away and
get trapped in the net. Not just in Egypt, but all over the world, people tried to shoo crop-eating birds from their fields with noises, scarecrows, and decoys.

Scarecrows might ward off some birds, but they don’t scare away the weeds, insects, or harmful fungi and bacteria. People have weeded and picked off insect larvae by hand, selected disease-resistant plants to cultivate, and even used chemicals to manage these smaller pests since ancient times. Certainly by 900
CE
, the Chinese were killing insects in their gardens with arsenic, and over the ensuing centuries people have found many ways to use chemicals to kill pests. Spraying nicotine-rich water extracted from tobacco is one; feeding poisonous seeds from strychnine trees to rodents is another; and spreading powder from natural toxins in pulverized chrysanthemum leaves is a third. In the mid-nineteenth century, commercially produced mixtures of sulfur, arsenic, lead, and other inorganic chemicals, which sold under colorful names such as Paris green, London purple, and Bordeaux mixture, came to the fore. People used these toxic mixtures to control mildew on grape vines in France and gypsy moths on apple trees in the eastern United States, until DDT appeared on the
scene in the mid-twentieth century.

In much of the world, throughout history and into current times, commercial chemical pesticides have not been an option. Like the Peruvian shifting cultivator, many cannot afford pesticides, or have no way to access them even if they have the money. Traditional farmers deal with the threat by managing their fields with the reality of pests in mind. Cumulative experiences passed down through generations have provided ways to lessen the damage. With multiple crops planted in the
same small field, traditional farmers do not risk the runaway damage that monocultures can entail. Consider a
milpa
farmer in the Guatemalan highlands who clears a small patch of jungle to make way for the three sister crops of Mesoamerica. A mix of corn, climbing beans, and different varieties of squash intermingle with other edible or medicinal plants, such as nightshade and tomatillo. The fields are not tidy, like one filled with neatly planted cornstalks, but if a harmful fungus were to take hold, it couldn’t run rampant like it did during the corn blight. The farmers let their hens in the field for a few days before planting, and the hens eat insects and turn the soil. They plant more than they need, claiming that “one seed is for the bird, one for the ant, one for me, and
one for the neighbor.” The farmers spread pesticides derived from chrysanthemum flowers, and occasionally a few ounces of synthetic insecticides in
case of bad outbreaks. The yields of the Guatemalan farmers cannot match the monocultures of the Corn Belt, but the risk of a catastrophic loss and the need for expensive pesticides are both far less.

Traditional farmers across Africa cannot afford commercial chemical pesticides. The bulk of chemical pesticides used on the continent goes for cash crops such as cocoa, coffee, and cotton, and to try to contain damage from migrant locusts. Traditional farmers have myriad ways to diminish damage from pests to fit their circumstances. Rice farmers in West Africa leave felled tree trunks in their fields to divert termites away from the growing crop. Kenyan farmers delay planting of sweet potatoes to avoid the peak season for the sweet potato weevil. Ugandan farmers use banana juice and pepper to discourage beetles from eating stored crops. The list of examples of strategies to manage pests is long, and many more likely exist but
have not been recorded.

It’s far too easy to over-romanticize the virtues of traditional agriculture as portrayed by these Guatemalan and African methods. Let’s not fall in that trap. The yields are low, farmers are vulnerable to the vagaries of weather, and daily life is defined by the struggle to produce
enough food so the family does not go hungry. But we should not overlook the benefits of these methods, either. Many of the same principles were moving to the forefront of economic entomology in the industrialized world during the first half of the twentieth century. “Nature’s own balance provides the major part of the protection that is required for the successful pursuit of agriculture. . . . [I]nsecticides should be used so as to interfere with natural control of
pests as little as possible,” wrote the American entomologist William Hoskins in a 1939 paper, “Recommendations for a
More Discriminating Use of Pesticides.” The principles he advocated included maintaining the diversity of crop types and varieties; rotating crops from year to year; fostering natural predators of pests, such as native lady beetles and spiders; and applying chemical pesticides only in low doses and only when needed. But before the entomologists could deliver on their goal to “diminish or remove the inherent dangers from the
use of poisonous insecticides,” as Hoskins stated, a new—seemingly miraculous—solution burst on the scene.

A Better Scarecrow

Dichloro-diphenyl-trichloroethane—DDT. Othmar Zeidler, a doctoral student at the University of Strasbourg, synthesized the chemical for his doctoral research. He received his degree in 1874 and didn’t think much more about its practical uses, unaware that the compound would set off one of the biggest pivots in food production in the second half of the twentieth century. Some sixty years later, the Swiss chemist Paul Müller again synthesized and then patented the compound. Unlike Zeidler, Müller was searching for an insecticide. He had found one, a very good one. Field trials showed DDT to be remarkably effective in killing the common housefly, the louse, the Colorado beetle, and the mosquito. In 1942, commercial DDT came onto the market with great promise for finally bringing humanity’s battle with pests to an end.