His friend Tony Bilotti went to Paraguay not long after Herren went back to Ibadan. He was visiting some fellow Americans serving in the Peace Corps, and he knew that he was now in a cassava hot spot in Latin America, the only one that Herren hadn’t had time to visit. Driving one day past a field of cassava, he noticed a few plants that looked a little funny. He stopped and plucked the leaves. Inside them he saw Herren’s mealybug.
When Herren got word, he had Bilotti send the insects to the British Museum, where entomologists could identify them precisely. Although the insects were dead, the entomologists recognized them as the species in Africa. And as they dissected them they discovered inside their bodies the true end of Herren’s search: parasitic wasps. Now Herren had the parasite that kept the cassava mealybug a minor pest in one corner of Paraguay, and the parasite he needed for Africa. He had entomologists in Paraguay send live mealybugs to England, where they could be raised under quarantine and the parasites could be captured as they emerged from their hosts. He sent mealybugs and cassava plants from Africa to the same quarantine, where scientists were able to get the wasp to lay its eggs in them. Even more important, the experiments showed that the wasps could lay eggs only in the cassava mealybugs. They hadn’t tuned themselves to the immune systems of other mealybugs, which could choke the wasp eggs in suffocating capsules. The wasps, Herren decided, would be safe to bring to Africa. Three months later, Herren got his first shipment of the wasps.
He was ready for them. He and his students at Ibadan had been building greenhouses where they could grow cassava infected with mealybugs and capture the wasps that thrived on them, and they figured out how to mate the wasps. After they had collected a few hundred of the egg-laying females, they made their first release in the fields around the Ibadan campus in November 1981. “Within three months, the mealybug population crashed. Then we knew we had something good going. It was barely a year and a half that we had gone from not knowing anything about this to having something in the field that worked.”
Biological control, even in its renaissance, remained a modest enterprise. Entomologists would raise wasps in their labs and load them into small containers that they’d take with them when they drove to orchards or corn fields. But a great dream took possession of Herren: to spread the wasp across Africa. “What I didn’t like in biological control was the way it was done as a shoestring operation, in a cheap way, using a secondhand beaker, raising wasps in some small cages—not done in the best possible way. That’s why biological control lost to chemicals.”
He knew that the dream would be expensive: $30 million, in fact. “That was when I was called a megalomaniac. I said, ‘Look, when you guys over in America have a fruit fly outbreak in California, which is only the size of a pin compared to this whole thing over here, you spend $150 million in one year. We’re talking about 200 million people who are at risk, not a few businesses that make oranges. We are dealing with one and a half times the area of the United States. We’re not going to do this in cages and on donkeyback and bicycles. We’re going to do this with technology, machinery, electronics, aircraft.’”
Maybe it was the word aircraft that made people suspicious. Herren claimed that he would be able to spread his wasp across Africa by sowing it, crop-duster fashion, from a plane. The wasps were put to sleep with carbon dioxide and then lodged in cylinders of foam rubber, two hundred fifty in each, which were loaded into a magazine that had been custom-built for Herren at an Austrian camera factory. As the pilot passed over a field Herren intended for him to drop the wasps precisely. “It was like in fighter aircrafts. You know when to drop the bomb by looking at the crosshairs. We tried this over a swimming pool in Ibadan. We’d fly over and drop the wasps. At one hundred eighty miles per hour, we were able to get them in there.”
In the meantime, the wasps Herren had set free in the fields around Ibadan had been thriving. Two years after their release, he decided to see how far they had spread. “We went on foot. We thought, ‘Oh, no big deal, we’ll just walk.’ And we walked the whole day, and we kept finding them. We thought, there’s something wrong here. Nobody had ever seen this sort of wasp spread more than a few kilometers. And the next day we came back and we took the car and we drove. We drove one hundred and fifty kilometers before we finally found no more wasps.”
By 1985, thanks to these early successes, Herren had collected $3 million of start-up money, and his pilots were strafing the countryside with wasps. The parasites tumbled out of his plane and landed on fields in Nigeria, in Kenya, in Mozambique, in countries from the Atlantic Ocean to the Indian Ocean. His team was raising 150,000 wasps every month, and although many of the wasps died during the long journeys from Ibadan to the release sites, he really needed only a single viable female wasp to survive the flight and the fall and to start looking for hosts. Even among parasitic wasps, the host-hunting skill of the Paraguayan species was extraordinary. “The wasp has developed an ability to search which is fantastic,” Herren says, with a pride that is almost paternal. “If you have one plant with mealybugs on it in a field that’s a hundred meters by a hundred meters, the wasp will find it. We tested this. We had fields that were clean. We put mealybugs on one plant, and we released the wasps from a corner of the field. Within a day they were on the plant. Then we tried something else. We put the mealybugs on the plant and then took them off. Then we released the wasps and they ended up on the same plant. There’s something that the plant releases that attracts the wasps, a cry for help.”
Herren trained twelve hundred people from the countries where the wasps had been introduced to recognize it. A few months after the drops, they began to comb through the fields to see how fast the wasp was spreading and how the mealybugs were faring. “Everywhere the problem was gone twelve months after the release. We could hardly believe it ourselves, that it worked so fast.”
The last flight of the wasp duster was in 1991, but for the next few years entomologists still went on tracking its effects. In about 95 percent of the fields where the wasp had been released, the mealybug had virtually disappeared. As they lost their hosts the wasps had diminished to only a few survivors as well. In the remaining 5 percent of the farmland, the mealybugs still thrived, but Herren was able to show why: the farmers didn’t take good care of their fields. Their plants were scrawny, and the mealybugs that fed on them tended to be scrawny as well. The species of wasp that Herren used is a careful judge of the size of its host, able to use its antennae like a ruler to figure out how big a mealybug is. Only then do they decide which sex to make their offspring. (When a female wasp mates, it stores the male’s sperm in a gland, which it can use later to fertilize its eggs. Thanks to wasp genetics, an unfertilized egg will grow up to be male, while a fertilized one will grow up to be female.)
The wasps choose to lay only males in small mealybugs. Their logic lies in the cheapness of males. The chances of an egg successfully maturing to an adult are worse in a small mealybug because there’s less food for the parasite to eat. Because the wasps put males in small hosts, only a few of them may survive to adulthood. But that doesn’t matter because it takes only a few males to inseminate a lot of females.