5

My Enemy’s Enemy Is My Friend

Let a man profess to have discovered some new Patent Powder Pimperlimplimp, a single pinch of which being thrown into each corner of a field will kill every bug throughout its whole extent, and people will listen to him with attention and respect. But tell them of any simple common-sense plan, based upon correct scientific principles, to check and keep within reasonable bounds the insect foes of the farmer, and they will laugh you to scorn.

—Benjamin Walsh, The Practical Entomologist

In 1958 Chairman Mao Tse-tung decided it would be a good idea to rid China of its pests. He stood, a plump and confident man, and pronounced the names of the animals he intended to exterminate. Fleas. Rats. Sparrows. Flies.

The idea of trying to kill off one or another species was not a new concept. Among the first uses for human tools was to get rid of species we didn’t like (and to eat the ones we did). One can tell the entire story of humans based on the things we killed at various moments in our past. What was novel was that Mao decided to do it on one day, across an entire country the size of North America. Mao was going big.

Everyone in China was ordered to do whatever he or she could to kill these four kinds of animals. The efforts were most conspicuous with the sparrows. People were ordered to go outside and bang pots and pans for forty-eight hours straight (taking turns) so as to cause the sparrows to fly in fear until they were exhausted and died. Sparrow eggs were also to be found and destroyed. And anything flying could, and should, be shot, in case it was a sparrow.

It is hard to know just how many animals were killed during this two-day episode. Mao’s government claimed quantities extraordinary in their magnitude and precision: 48,695.49 kilos of flies, 930,486 rats, and 1,367,440 individual sparrows. Whatever the true numbers, sparrows in particular were incredibly rare after this killing spree. Cities and countrysides went quiet. This was a victory for Mao in that his plan had been successfully carried out. Unfortunately, tree sparrows, the most common sparrow in China at the time, eat far more insects than grain and benefit crops by controlling pests. They are, or were, secret agents of biological control (a fact known by ornithologists but ignored at the time). Once the sparrows were gone, pests in crops reached outbreak levels. The crops began to fail. Had this been a problem in isolation, things might have been okay. But Mao made many other decisions that contributed to food scarcity. As a result, the greatest famine in human history ensued. At least thirty million, perhaps as many as fifty million, Chinese people died. This famine, like many others, was caused by the actions of a human leader. But its horrors were magnified by the release of crop pests from their enemy the sparrow.

Mao’s plan failed to account for a phenomenon ecologists call a trophic cascade: changing one species in a food web (say, sparrows) can lead to changes in many other species that it feeds upon or that feed upon it. For ecologists these cascades can be beautiful inasmuch as they obey predictable rules, the invisible laws of nature. Remove a predator, and its prey will thrive. Remove the predator of a predator, and prey become rare.1 Hans Herren was hoping that the cassava ecosystem would be similarly predictable, that he could find a parasite that would eat the mealybug and so allow the crops to thrive once more. His plan was to do the opposite of what Mao did. He was hoping he could bend ecology’s rules in his favor—or, rather, in the favor of millions of Africans.

Efforts at biological control include some of the greatest and most tragic examples of hubris in biology. Beginning in the 1840s, cane toads (Bufo marinus) were intentionally introduced throughout the Caribbean to control, initially, rats, then pests that affect sugarcane, particularly white grubs (Phyllophaga spp.). The cane toads thrived alongside the rats, which they did not control. By some accounts they did not control the white grubs, either, but they were introduced into Hawaii and the Philippines anyway, where they also might or might not have controlled white grubs and other pests affecting sugarcane. In 1935 hundreds of cane toads were sent from Hawaii to Australia in hopes that the cane toads would control the greyback cane beetle (Dermolepida albohirtum), the larvae of which consume sugarcane roots. Only after the toads’ introduction did people realize that the animals don’t jump high enough to eat the pests. They are, however, doing just fine on other foods and are now devouring rare native species and killing anything that tries to eat them, including rare snakes and domesticated dogs. The toads are ranked by some as one of the greatest threats to Australian biodiversity. We tend to hear more about cases in which biological control agents have unintended consequences than we hear about the far more common cases of failure in which biological control agents have no effect at all.

Advocates of biological control will tell you that these failures are historical—or, as the plant pathologist Harry Evans (see here) more strongly put it, “unscientific anecdotes,” meaning that the method’s success has become far more common than failure. Yet the examples of great successes, successes that changed the world, were, in the 1970s, still few. From the start, cassava did not seem likely to be a success story. For one thing, no one knew anything about the cassava mealybug, not even where it came from. For another, the scale of the problem, geographically, was immense, potentially covering all of tropical Africa and parts of Asia. Yet no other solutions presented themselves.

The first step was to find where the mealybugs had come from. Then, having found that, the next step was to look for animals and other organisms that eat them. But Herren and his colleagues had nothing to go on other than their knowledge about the natural distribution of cassava and the indication from the French biologist Danièle Matile-Ferrero, based on a museum record of a similar mealybug in Brazil, that the pest was probably from the Americas. She could not even pinpoint a continent. This may seem outrageous, that a new and devastating crop pest would emerge out of the unknown. But when most species on earth are unnamed, unnamed species appear on crops and in our backyards all the time.2 It is ordinary. No one remarked at the unusualness of the situation,³ only at its difficulty. Herren guessed that the mealybug came from the place where cassava had been domesticated or where the majority of its relatives lived. He just needed to find out where that was.

In the 1960s, a Texas oilman named Kenneth Lee, along with several geographers, argued that cassava had been farmed at high densities in the Bolivian Amazon and likely in nearby Paraguay and Brazil. Botanists, at around the same time, argued that it was in approximately this same region that cassava had originally been domesticated. These hypotheses together suggested strongly that the first place to look for a strange cassava pest would be in this region. Unfortunately, although it is now clear that they were right, the opinions of these individuals were viewed as heretical by anthropologists who thought that large-scale agriculture could never have been possible in the Amazon. As a result, to the extent that these ideas were present in scientific literature, they were quiet, radical, and obscure. Herren might have nonetheless paid them heed and started looking for cassava mealybugs in Bolivia, Paraguay, or nearby parts of Brazil. He was a bit heretical himself, of course. But he did not.

Herren decided on a five-step plan. He would travel to each of those places where relatives of cassava lived, starting in California. He might have been lucky; the mealybug might have been native to Southern California, and he might have found it right away. It was not. California was a bust. Herren headed south into Mexico, from one patch of cassava to another. He ran afoul of guerrillas and governments in equal measure. In his travels, by his own account, he was arrested, “nearly killed,” or both many times. Even if one takes into account the possibility of hyperbole, it seems clear that Herren faced real danger—danger on behalf of Africans he had never met (and their children and grandchildren). When he did, when he was in jungles far from the Switzerland of his childhood, afraid, he must have wondered whether the whole endeavor was lunacy. On farm after farm, in Mexico, Guatemala, Honduras, El Salvador, and Nicaragua, he found nothing.

Then, in northern Colombia, he found something; a cassava mealybug that looked like those he had seen in Africa, eating cassava plants in much the same way as the cassava mealybugs in Africa did. He thought it was the right mealybug, the one plaguing Central Africa. It was not. Nor was this the first time someone had made the same mistake, but even figuring out something so simple as whether it was the right species was a major challenge when so little was known.4 The bug was new to science. It was yet another new species, another unnamed cassava eater, a species that, whether as insult or praise, bears Herren’s name, Phenacoccus herreni.⁵ The bad news, of course, is that its predators and parasites were likely to be totally ineffective in controlling the cassava mealybug in Africa. They were the demons of a different pest.

Herren went back to searching. He had been to Mexico, Central America, and northern South America. Researchers from the Centre for Agriculture and Biosciences International (CABI) had searched in Trinidad and northeastern South America. The next place to try was Paraguay. To travel to Paraguay, Herren enlisted the collaboration of Tony Bellotti, who was by then working at the Centro Internacional de Agricultura Tropical, in Colombia. Bellotti wrote the book, or at least the major paper, on the pests affecting cassava in 1978 and worked in the years since then throughout the neotropics. Glad to help, Bellotti took Herren to Paraguay with him in the wet season of 1980 to look for the mealybug. They found nothing. Herren begged Bellotti, who would be back later in the year visiting his ex-wife, to check again when it was dry. Bellotti did, and when he did, he found what appeared to be the cassava mealybugs. He contacted Herren. He also quickly sent samples to Doug Williams at the Natural History Museum in London (who had just named the mealybug Herren had found in Colombia). Williams, perhaps the greatest expert on mealybugs in the world at the time, identified the insect as the same Phenacoccus manihoti that was terrorizing Africa. They had the right mealybug, thanks in part to Bellotti’s meeting with his ex-wife.

More surveys began in Paraguay in earnest in 1981 in a collaboration involving Herren and his team, Bellotti, and researchers from CABI. The cassava mealybug was present in many fields in Paraguay, but nowhere abundant, nowhere destroying whole fields, suggesting that it was being held in check by its own devouring monsters, exactly what Herren had hoped for. Then in 1982, the mealybug was also found in Bolivia, in precisely the region where cassava was not only native but also cultivated at very high densities, high enough to favor the origin of new pests—such as the mealybug and certain pathogens—and perhaps even the species able to control them over the thousands of years during which cassava was farmed there.6 It was right where it would have been predicted, at least if cassava’s history were more generally known.

Bellotti thought he had found the needle in the haystack, the mealybug in its native range. Now he, Herren, and others needed to thread the needle: they needed to find species that ate the mealybug and figure out a way to spread those species across Africa. In Paraguay, they watched the mealybugs in the field. They cut open adults. They poked and prodded. The mealybug seemed to have many enemies, including fungi that devoured its body, ants that dragged it home and fed it to their babies, and, most promising, wasps that laid their eggs inside the mealybugs’ bodies. Eighteen species were found preying upon and parasitizing the cassava mealybug.⁷ Biologists are biologists because they love life. No organism is good; none is bad. Each is a manifestation of the marvelousness of evolution. Yet for Herren and his colleagues, one life form, the mealybug, was clearly the enemy, and the organisms that consumed the mealybug were beginning to seem a great deal like friends.

Among the most common of the creatures found attacking the mealybug was an animal called Lopez’s wasp, Anagyrus lopezi.⁸ This wasp was promising. It was fecund, specialized (appearing to feed only on cassava mealybugs), and, in its method of killing mealybugs, brutally efficient. Lopez’s wasp lays its eggs inside the bodies of the mealybugs. There the larvae hatch and eat the mealybug’s blood, then its muscle, then its fat, then its digestive tract, all the while being careful to leave the nervous system of the mealybug intact. The wasp then molts, chews a hole in the exoskeleton of the by-then-empty shell of the mealybug, and flies away to mate.9

Scientists at CABI arranged for several Lopez’s wasps, along with individuals of seven other parasite and predator species, to be sent to the Natural History Museum in London. From there the parasites were transferred to the CABI quarantine unit, where they were allowed to live through several generations and were minimally tested for their negative effects on organisms other than the cassava mealybug. Having passed these tests, the insects could be taken to Africa.¹⁰

In 1981, the same year in which the wasps were first found in Paraguay, Herren flew from London to Nigeria with some of these wasps in his luggage, packed in vials stuffed with paper and honey (to keep the wasps alive) and topped with cotton. He got off the plane energized. He’d pop the cap, release the beasts, then watch his winged army rescue a continent. But this was just a daydream; in reality Herren knew that spreading the wasps would require active intervention. He would need to rear many and then spread them himself, or at least spread them with his team, from country to country. This would take time, which those who subsist on cassava did not have. The only substitute for time was money.

Herren thought he would need millions of dollars in order to introduce the wasps at many different places simultaneously. In the event the first batch didn’t take, this technique made it more likely that at least some would and that it would happen fast. Herren wanted—needed, he would say—a three-story building, a kind of giant insect fornicarium, in which to breed the wasps. He needed three airplanes to release the wasps once they were ready. He needed assistants to carry out the tedious rearing. Relative to the societal and economic costs of the mealybug, the cost of these needs was minor, but only if Herren were to make his plan work, and no one really believed he would.

He asked for $30 million. He got $250,000 from a UN agency. Even with this sum, his colleagues thought he had been disproportionately favored in a world where everyone was clamoring for funds for some good and necessary project. As Herren continue to knock on doors for more funds, he simultaneously started to move forward, begging forgiveness after each radical action rather than asking permission beforehand. His bosses at the International Institute of Tropical Agriculture were furious with him half the time and irritated with him the rest of the time. To many, Herren was “another ecofreak fresh out of Berkeley.” The institute wanted to breed new strains of cassava or spray pesticides rather than deal with biological control. Everyone knew that the odds of success from breeding new cultivars were much higher than the odds of success from biological control. Everyone also knew that breeding new strains of cassava would take a long time and that many people would die as the mealybug spread; this was an inevitable reality of the more certain path. And pesticides were not a realistic option as long as the goal was to help poor farmers.

Eventually Herren and his colleagues at the IITA raised $6 million; it would have to be enough. With this money, they designed and built rearing facilities twelve feet high, inspired by the hydroponics tower at Disney World. Within these facilities, when everything was working, they could rear one hundred thousand wasps a week. But most of the time everything did not work; most of the time, wasps died. And even once the rearing facility was working there was another challenge: they would need to distribute the wasps across Africa. They bought a plane. They would use the plane, a twin-engine Beechcraft once used by the CIA in Asia, to shoot vials of wasps through the air into farmers’ fields. But what would they shoot the wasps with? They invented a special device, a sprayer that would propel the wasps out over the fields while alive and intact. The wasps were the heroes; one had to be careful with their delicate wings.

Meanwhile, few came to help, and the news crews did not call. We disregard the slowly building tragedy, the tide rising in slow motion toward someone else’s town. Yet the tragedies that occur when tropical crops fail affect us all. They affect us as refugees from hunger flee their native countries. They affect us in terms of our own food supply. You already consume cassava in some processed foods, even if you do not know it. Tapioca is made from cassava, as is most MSG. In other words, even if the plight of hungry families is somehow unmoving, the loss of cassava from mealybug damage is likely to make your pudding and udon noodles more expensive. What’s more, cassava is projected to be a crop humans will depend upon more in the future rather than less.

What will grow in any given patch of dirt on earth is changing. It has been changing for a while. As it changes, the cost of our food will change, and as it does, what we eat will, too. For all but the fabulously wealthy, the price of our food affects what we buy, what we eat, and what gets put into processed foods.

The first change that has affected and will continue to affect what is farmable is exhaustion. The soil in most places we farm has been pushed, pulled, kneaded, and squeezed until all the juice once in it is gone. We attempt to fix this by applying fertilizer, but our abilities are limited. As a result, what you can farm in Minnesota is not the same as it used to be. Corn will not grow in many of the places it grew in the 1950s. We talk about ancient, old-growth forests. One might also describe ancient, old-growth soils. Such soils do not, for the most part, exist anymore, except on steep slopes or other places too difficult to farm. The children of farmers face different choices from those their parents faced.

But compared to what is coming next, exhaustion is a small concern. The bigger challenges are changes in climate. Each cultivar of each domesticated plant species has a specific combination of temperature and precipitation in which it can live. We are changing both temperature and precipitation levels. We can, when there is enough water, modify precipitation. We are rainmakers. But only up to a point, and always with costs. We can’t undo the changes to temperature.

As scientists have studied the ways in which plants and animals move, acclimate, and adapt to changes in climate, they have made some observations that seem obvious in retrospect. Species that live at the tops of hills will face particular challenges. The cold climates they need will disappear. Species in the middle ground will move uphill, but into smaller geographic areas than they once inhabited (mountains are narrower on the top). Species at lower elevations may move up. But what happens to the species at the bottom, the species living on the flatlands, where most of us live and where most of our food grows? All things being equal, crops from warm places will move north. Crops currently growing in North Carolina will need to grow in Michigan, and those growing in Michigan may shift to Canada. But what about the vast tropical stretches of the planet? In these places, hot conditions may become hotter and drier. Entirely new climates are predicted to emerge. Under such conditions, we do not know which species will succeed. Nor do we know which species we will be able to farm; such species will have to be tough or die. We will have to be tough or die. We will, almost certainly, have to eat more cassava.

Cassava is marginal in more than one way. It is marginal relative to daily Western life, at least for now. It is also marginal in that it grows where little else will. This is what makes it important for the future—more important to you rather than less. No matter whose model of the future you consider, the number of humans who will live with us on earth is increasing. The global demand for food will double by 2050 because of population growth in developing countries—those “marginal” tropics—and the demands of that population. (This doesn’t take into account the increase in consumption in developed countries.) These demands will occur in regions that today are generally difficult to farm in. But with global warming, farming in these hot lowland regions will be even more difficult.

Consider Africa. While eastern Africa is predicted to get hotter and perhaps wetter, both northern Africa and southern Africa are predicted to get both hotter and drier. Potatoes are predicted to get harder to farm, as will bananas, plantains, beans, maize, millet, and sorghum. When agricultural scientists such as Andy Jarvis and his colleagues at CIAT, in Colombia, where Tony Bellotti worked, consider the future of tropical agriculture, they predict that there will be more cassava and less of nearly everything else in Africa.11 Similar realities are likely to emerge elsewhere in the tropics. Cassava grows from nothing, requires little fertilizer, and is robust during dry years and hot years. But all the advantages of cassava would be useless unless Herren or someone else could control the cassava mealybug. All of which is to say that it was not just the fate of those in Africa and Asia that depended on Herren. It was also the fate (or pocketbooks) of all those who buy cassava and its products anywhere in the world or who might buy it in the much warmer future.

Besides Herren and his colleagues at IITA and CABI, the other people attempting to deal with the problem were the farmers themselves. They dealt with it the way that farmers always have: they changed the varieties of crops they were using, favoring the kinds of cassava that seemed best able to withstand the mealybug. Where the diversity of a crop such as cassava is great, this process can be quick. A cultivar that does not die is replanted, traded, sold, and treasured. But in Africa the diversity of cassava varieties was not great. It was a tiny portion of what was present in the Amazon.12 Yet it seemed to be enough to help. Farmers favored the more resilient cassava, which, as it turns out, tended to be the bitter strains, strains evolved in the Amazon to be toxic to cassava-eating herbivores, including humans.

As West Africans fed more bitter crops to their children, Herren’s team tried to breed more wasps, millions of wasps. But Herren himself was coming apart—fraying at the edges from lack of sleep, too much work, and the pressure of believing that a whole continent depended on him—even as everything was coming together. He decided to test the handful of wasps that had already been reared. In November, the dry season, of 1981, Herren released the first wasps in Nigeria near his own workplace. Then he and his colleagues waited. At first nothing. The cassava died. Leaves wilted. Farmers cursed both the mealybug and Herren and his team.

Then the news seemed to change. Some of the fields were doing better; some of the mealybug populations were doing worse. The wasps were a success in the farms in which they were released in Nigeria. The cassava grew strong, healthy, and green. In addition, the wasps survived the wet season. They made it to a second year. Wasp releases were done again 1982. Those wasps, too, would survive the rains.13

Amazingly, the next steps were also successful. The wasps bred well in captivity. They could be released on the ground or, rarely, from the plane. Soon Herren and his colleagues released them both on the ground and from the plane in nine countries. By 1986, wasps were released in fifty sites, a number that would grow to 150.¹⁴ Some countries begged for wasps; others quietly permitted them. Cameroon declined but got wasps anyway when they flew in from neighboring countries.¹⁵

In the meantime, the mealybug plague had grown far worse and more geographically expansive in places where the wasps had not been released. By 1983, cassava mealybugs had reached the status of an outbreak. In Ghana, farmers lost 65 percent of their yield (a $58–$106 million loss at the time). The price of cassava in the market increased ninefold. The price of planting material—new cassava—increased by a factor of 5.5. Where the mealybugs were present, farmers had to plant two or three times as much crop in order to get the same amount of food as they harvested the previous year. Often they did not have the land, or the time, to do this. Hunger loomed; to those who remembered history, events bore a striking resemblance to the buildup to the great potato famine, except that rather than just an island a whole continent was at stake. A lot depended on the tiny wasps.

Finally a new kind of news started to come in, news of mealybugs disappearing in places far from the wasp release sites. At last the wasps were spreading! By March of 1983, just two years after the first release of wasps (ten wasp generations), wasps could be found in every cassava field within a hundred kilometers (sixty-two miles) of each of the release points. Not only was this fast, it was also the fastest rate of spread ever recorded for a parasitic wasp of any kind.¹⁶

Millions of released wasps turned to billions in a few years. Cassava grew back, almost magically. In Nigeria, cassava production increased from fifteen million tons before the wasps to forty million after them.17 Across Africa in general the change was similar. A tiny wasp had saved millions of people, potentially hundreds of millions, thanks to the man who midwifed them across continents and the relatively few others on which so much had come to depend. By conservative estimates, the benefits of the biological control program relative to its cost could be expressed as a ratio of 149 to 1.¹⁸ Less conservative estimates put the benefit-cost ratio at 1,592 to 1. And these estimates don’t even include the added benefit of not having to use pesticides.¹⁹

There is no caveat to this story; it is just an unadulterated success. Cassava mealybugs still exist in African cassava, but they are kept in check by the trophic level above them. This is not the balance of nature. Nature is far more often in open war than in balance. It is instead something far more precious and yet attainable: the balance of agriculture.

Figure 5. Dollars spent introducing parasitoid wasps to Africa to control cassava mealybugs compared with dollars gained by African economies because of the introduction. Estimates are drawn from Jürgen Zeddies, et al., “Economics of Biological Control of Cassava Mealybug in Africa,” Agricultural Economics 24, no. 2 (January 2001): 209–19. Figure by Neil McCoy, Rob Dunn Lab.

Thanks to Herren and the more than three hundred people who worked with him on the mealybug project, a pest that threatened to produce an African famine of unheralded proportions was controlled. By 1987, the wasp had spread to virtually every farm growing cassava in West Africa. All this happened in a little more than a decade. One can debate why the late blight killed so many in Ireland, why the potato famine was so boundlessly tragic. With the story of the cassava mealybug there is no such ambivalence. Millions were saved because of the work of hippie biologists who believed in biological control, a bunch of entomologists, an ex-wife, and a previously unknown wasp species that continues to do its biocontrol work on our behalf to this day.

Meanwhile, in 2008, the mealybug was found for the first time in Asia—in Thailand, where it had likely spread via the cuttings of cassava stems.20 By 2009 it had spread across seven hundred square miles. By the time it was discovered, Tony Bellotti had retired (he has since died). Herren had moved on to leadership roles (though he continues to work). Danièle Matile-Ferrero, the taxonomist who gave a scientific name and formal identity to the cassava mealybug, had retired (and hence was no longer being paid), but she was still doing her work.²¹ What one might hope is that, in their places, one could find a new generation of experts poised to play similar roles, along with even more support, more funding, and better facilities. The good news is that a new generation has been trained, a generation on which we might hope to depend. Yet when Thai scientists found the cassava mealybug, they brought in one of the retired superstars of the earlier generation, Bellotti, to help. The Thai scientists, in consultation with Bellotti, developed large-scale rearing facilities for Lopez’s wasp. They released the wasps. The wasps have spread successfully.

In this story of the cassava mealybug in Thailand, one finds another round of heroic work by unheralded biologists. But one also encounters a reason for humility. The cassava mealybug is a known problem yet still could not be kept from arriving in Thailand (or, subsequently, Vietnam, Malaysia, Indonesia, and Laos). Nor should we forget the other humbling aspects of the story: when the cassava mealybug was found, it was not yet named; in looking for the cassava mealybug, a handful of other new cassava mealybug species were found; and among the pests attacking those species—the secret agents of biological control—virtually none of them had names, either. In an ideal world, if we want to keep our crops healthy, we should have full lists of the pests attacking our crops and great zoos of the organisms that can be used to control them, zoos at the ready when they are needed. We don’t. Cassava may well be the future of tropical agriculture. If it is, a relatively small group of entomologists has played an outsize role in allowing such a future to be possible.

Meanwhile, we should ready ourselves for the next wave of pests. In the Democratic Republic of the Congo alone, according to Sarah Gurr, more than 95 percent of the pests and pathogens that can (and likely will) arrive from their native lands have yet to appear. And Gurr studied only those pests and pathogens that have already been discovered and named. In the days before the cassava mealybug was noticed in West Africa, a study like Gurr’s would not have noted it as one of those yet to arrive. It is too hard, and it costs too many lives, to try to understand the pests that attack our crops only during emergencies. We need to do thorough studies of these pests in advance. The monsters need to be named and known. How can we go about this?

We need to survey all the traditional crops we can, particularly those not being sprayed with pesticides, and find the pests on them. We need to survey those pests and find the species that eat them. While we’re at it, we need to understand the mutualists of these crops, their partners—the animals that pollinate their flowers (the pollinator of cassava remains unknown), the fungi that live in and defend their leaves, the microbes that help their roots extract nutrients from the soil. Some of these studies may require us to go to remote communities. Or, alternatively, we can engage families in those communities to help us to study the species associated with traditional crops. This may seem like a difficult proposition, but think about the case of a crop native to North America, squash. Squash is pollinated by a specialist bee that depends on the squash plants and has, it’s been shown, spread as squash plants have been moved. But the pests affecting squash and their enemies are less well understood and in some cases haven’t even been named yet. It would not be hard to distribute seeds to kids in schools across the United States so that they could plant traditional varieties of squash and, in doing so, document pollinators, pests, and natural enemies. It just hasn’t been done yet.

Once we know the species associated with each crop, we need to figure out how to grow them, study them, understand them, and use them to our benefit. How many species might this include? Gurr considered several thousand pests and pathogens but was quick to acknowledge that many more remain to be discovered and named. Let’s say, conservatively, that four thousand species of pests and pathogens exist and that each of those pests and pathogens falls victim to five parasitoids or pathogens capable of controlling it. Then we are talking about twenty thousand species of pests, pathogens, and enemies that need to be studied, saved, cultured, understood, and held at the ready for the time when they are needed. This is to say nothing of the mutualists; crop mutualists are an even greater mystery and might include hundreds of thousands of species.

Many grand challenges in biology are not achievable. This one is, yet we are nowhere close to achieving it. We have barely begun to try. This is not a critique of those who work in the field identifying these species and figuring out their biology, their needs and limits. It is instead a critique of what we have chosen to invest in as a society. It is a critique that is necessary, because while the incremental benefit of studying some insect or fungus species might be small and slow to accrue, the loss of not having studied it can be enormous and immediate, as has proved to be the case with cacao, one of the most endangered crops on earth.