Before starting his own insectary north of Escondido, Jim Davis Worked for a big citrus grower in Corona, near Riverside. At one time, this grower, like most of his peers, spent a lot of time and money spraying chemicals on his orange, grapefruit, and lemon trees. At least fives “key pests” plagued the fruit and could only be controlled with insecticides, or so everyone believed. But the Corona grower decided to experiment with a tiny wasp under study by some UC Riverside scientist. It seemed adept at attacking California red scale, one of the worst agents of citrus destruction.
Out in the grove, the wasp didn’t appear to do much for two years. But in the third year, “the whole ranch turned around,” says Davis. “They found the wasps everywhere and the pests just went down to nothing.” Not only did the red scale disappear, “it turned out that all the other pests were really secondary ones that were created by the [chemical] sprays.” Once the spraying ceased, their natural predators got established well enough to control them. As a consequence, the grower went from spraying his 2000 acres four times a year to spraying a tenth of his grove once a year. “They’ve saved $250,000 a year on pest control,” Davis says.
By 1985, when Davis went to work in the citrus grower’s insectary raising the predatory wasps, ranch veterans told him that the trees were looking better each year — greener, healthier, and with more fruit set. The pesticides, which contain solvents that remove wax from the leaves, had been subtly damaging the trees over time. “They weren’t unhealthy,” Davis says, “but they just hadn’t been as healthy as they could be.”
Davis talked to other farmers who’d gotten wind that something interesting was happening. “Every year we’d get a few more calls, a few new clients [for the wasps], a few more acres,” Davis says. He says he always warned the would-be wasp buyers, “You’re going to suffer the first year. You’re not going to get the yield that you have been getting. You’re going to have more fruit rejected in the packing house.” The second year they could look forward to things being about the same as they were under their customary chemical regimes, Davis told them. “And the third year, the Aphytis [wasps] are going to be everywhere, the red scale’s going to be gone, and you’re going to be in heaven.”
Davis quotes Paul Debach, one of this century’s most articulate proponents of biological pest control, who compared pesticide use to heroin addiction. “Once you start, you can’t stop,” says Davis. “And that three-year period was like the withdrawal period. That’s what it took to get the growers off the drug. After that, they were clean, and instead of calling me up and saying, I’ve got this horrible pest infestation. What can I spray?’ they would say, I’ve got this horrible pest infestation. I can’t spray! What can I use?’ because they didn’t want to get back on the drugs and have to go through that three-year period again.”
Today at least 20,000 acres of Southern California citrus trees (about 20 percent of the total) aren’t sprayed at all, thanks to the wasp, Davis estimates. He says the Corona insectary was selling huge quantities of the insect — some $60,000 worth per month — at the time he left four years ago. Since then, one of his former employers has started an even larger insectary in the San Joaquin Valley, where more than half the state’s citrus fruit is grown. Although growing conditions in the central valley make it tougher to use the scale-munching wasp, a strain has been developed that’s adapted to those conditions, and “now they have a program up there,” Davis says.
The long history of biological pest control abounds with similar success stories. Ancient Chinese growers used an ant to control caterpillars and beetles in their citrus orchards. By 1776 Europeans were pitting a predator called Picromerus bidens against the common bedbug, which it reportedly devoured. Even the “modern” era of biological control began more than 100 years ago — right here in Southern California — when a tiny beetle saved the nascent citrus industry from extinction.
In 1886 the industry was under attack from something called the cottony-cushion scale, an insect whose female exudes a puffy white mass containing hundreds of eggs. Infected trees looked as if they were studded with popcorn; eventually they turned black and died. “Damage was so extensive that many growers pulled out or burned their trees, and real estate values plummeted,” writes Paul Debach in his 1974 landmark book, Biological Control by Natural Enemies.
To the rescue came the USDA’s chief entomologist, Charles Valentine Riley, who discovered that the pest was native to Australia, where it seemed to be harmless. Something was eating it, keeping it in check. Riley reasoned that if that something could be brought to California, it might be able to do the same job here. By 1888 he and others got the federal government to pay $2000 to send entomologist Albert Koebele across the Pacific Ocean on a collecting trip. Koebele shipped back specimens of two potential cottony-cushion scale enemies: a ladybug beetle known as Vedalia cardinalis and a parasitic fly. They traveled on sailing ships in ice-filled compartments, and by April of 1889, the beetles were being distributed to sites throughout California. Little more than six months later, they had cleaned the cottony-cushion scale so thoroughly from the citrus trees that the pests could scarcely be found. To this day, “Wherever you find them, you find the Vedalia beetle and the parasitic fly,” Davis comments.
He says it was stories like this that first kin died his interest in agriculture. Raised in Ohio, he studied biology and ecology in college, and after getting his undergraduate degree, he decided to become a pest-control advisor, one who could counsel farmers on how to use beneficial insects to solve their pest problems, rather than pesticides. “ ’Cause it’s pretty much accepted, pesticides are not really such a great way to go,” he says.
That’s a temperate assessment of a situation that has driven some observers to near-hysteria. Concerns about modern pesticides, first introduced in the 1940s, began surfacing as early as the 1950s and burst into the American national consciousness by 1962, with the publication of Rachel Carson’s Silent Spring. As powerful as that warning was, by 1992 nearly five times as many pesticides were being manufactured for use in American agriculture, forests, homes, and for export than there were when Carson’s book was published. About 200 million pounds of pesticide are used every year in California alone, according to the National Resources Defense Council.
Delphastus pusillus larva feeding on silverleaf whitefly
Jack Kelly Clark
UC Statewide IPM Pest Project
These chemicals, which until the late 1970s were not expected to invade groundwater, now are thought to be contaminating many resources, including surface water, rain, and even fog, according to the NRDC’s 1991 report, Harvest of Hope. Among other studies, that report cites a recent Environmental Protection Agency estimate that 9850 (or 10.4 percent) of the community water system wells and 446,000 rural domestic wells (4.2 percent) in the United States contain at least one pesticide or pesticide degradate. “EPA’s survey reveals that, at a minimum, over 1.3 million people are drinking water contaminated with one or more pesticides from private wells...” the report states.
The pesticide proliferation has not brought about a concomitant decrease in harmful bugs. In 1945 insects destroyed 7 percent of American farm crops, compared to 13 percent in 1990. Under the constant bombardment from the chemicals, many plants appear to grow weaker and thus more vulnerable to insect attacks, while the insects have grown ever stronger. Some 447 species of insects and mites had become resistant to pesticides by the late 1980s, according to government sources.
Davis adds that pesticides create secondary problems for farmers. “Generally these pesticides will kill the predators and parasites much more effectively than they will the pest itself. So after you spray, there’s a resurgence of the pest because you’ve wiped out everything that’s eating it. And so it comes back even worse. In an unsprayed situation, you’ll have other pests that are being eaten by their natural enemies. They’re present, but they’re not really causing any damage.” When spraying wipes out those natural enemies, a new troublemaker seems to materialize. “They’re called upset pests. Because they only become pests when you upset the system,” Davis explains.
Seeking a master’s degree in pest management, Davis in 1982 headed for the campus of UC Riverside, whose entomology department was considered to have one of the best biological control divisions in the country. But what Davis heard in his classes there disconcerted him. “All the professors were saying, ‘These are the biological control agents. These are the things that eat that pest — but they don’t really work, so this is what you’ve got to spray.’ ” What they meant, Davis learned, was that the predators and parasites that were needed to control the pests were not commercially available. “Here I was going through this program, when I realized that I couldn’t do what I wanted to do because nobody was growing the things I wanted to use. And it’s not economical if you’ve got to just sit there and tap your foot and wait for them to fly in from someplace.”
Davis says that’s when he became interested in learning how to grow “beneficials.” He wanted to help increase the number of weapons in the biological pest controller’s arsenal. He dreamt of one day making enough money to fund university research, something that today is primarily supported by chemical companies. “I know that the entomologists would much rather work on biological control than on spraying chemicals,” he affirms. “It’s much more interesting. It’s ecology; it’s not just seek and destroy.”
To get some practical experience at growing insects, Davis first took a job with the USDA quarantine station located next to the entomology building on the UC Riverside campus. Insects imported from abroad must go there (or to one of six other USDA facilities) for a period of observation and study. “First they’re exposed to the pests to ensure that they actually do attack them. And then you start studying their other behaviors,” says Davis. That’s not as daunting as it might sound. The entomologist points out that beneficial insects normally don’t eat any plant material. They eat other bugs. So you don’t have to worry about their creating some agricultural plague that will overshadow the initial one. In the rare cases where a bug is brought in to eat weeds, “They have to test it against every desirable plant in the country before they can let it out of quarantine. It generally takes 15 years to find [an insect] that will only eat the weed. A researcher in that field, if he’s lucky, can do two projects in his lifetime.”
It’s not practical to test a potentially beneficial bug against every other bug in the country, nor is it necessary, since the beneficials usually have an extremely limited range of prey. “These things are the insects that feed on the pests where the pests evolved. All we’re doing is introducing them into the new area that the pest got introduced into,” Davis says. “The big problem is that sometimes they don’t survive as well in the new climate. It’s either too hot or too cold or too wet or too sunny or too shady or the day lengths are too long. Or something.”
But leaving the quarantine facility and working in the Corona insectary gave Davis a taste of how satisfying life can be for the bug commander who overcomes those logistical problems. I imagine him brimming with optimism when he arrived in San Diego County four and a half years ago. He worked as a pest-control advisor for about a year and found a business partner in the Rodriguez family, owners of a 100-acre farm that grows organic vegetables and flowers. They agreed to contribute both money and some greenhouses where Davis could raise his six-legged assassins. And Davis had a couple of enemies targeted, including a minuscule white glutton known as the sweet potato whitefly.
Were this whitefly to land on your shoulder, you would never notice it. Or you might mistake it for a flake of dandruff. It would be that innocuous. But were it to multiply — reproducing thousands and millions and billions of itself — you would see some agricultural destruction of biblical dimensions.
Imperial Valley farmers got one of their first glimpses of the whitefly’s destructive powers around 1980, when an infestation in the desert agricultural community drove the price of iceberg lettuce from 29 cents a head to a dollar or more. That plague prompted USD A officials to consider using classical biological control against the pest; around 1984 they started importing potential whitefly killers from Jordan and Pakistan, says Davis, who was working at the USDA quarantine lab at the time. In fact, some of those recruits were the first bugs he ever grew, and some of them were released in weed sites near the valley’s agricultural fields. “But it was essentially doomed from the beginning,” Davis says of the effort. “The way [the desert farmers] sprayed virtually insured that the whitefly would continue to be a problem.”
The lettuce farmers changed their cropping practices enough to foil the pest for a while, but by the end of the 1980s a stronger strain of the whitefly had emerged (today it’s called the Strain B or silverleaf whitefly). Like other whiteflies, it damaged crops most by robbing them of their nutrients. Davis explains that in a healthy plant, “water moves up into the leaves where photosynthesis takes place — production of carbohydrates and other materials. Food.” This food combines with water to form sap, which moves back down through the plant to the roots. However, the whitefly interrupts the normal process by sucking out the sap “until there’s so little that the plant can’t maintain itself and it dies. The white-flies basically tap into the food production of the plant and use it all up.”
In the fall of ’91, Imperial Valley and Baja farmers watched their melon plants struggle up for only a few inches before dying from the results of the insects’ onslaught. The whiteflies also annihilated fields of broccoli, cauliflower, alfalfa, squash, lettuce, tomatoes, and more — . a wide range of targets. In the cotton fields, where the insects resembled a snowstorm and were so concentrated that pilots could see clouds of them from their airplanes; the whiteflies’ excrement, called honeydew, made the cotton lint sticky and hard to gin. And a black mold grew on the sticky substance and made the cotton fiber gray instead of white. When Imperial Valley farmers totaled their losses by April of 1992, they figured that the whiteflies had caused at least $130 million more in crop damage over the previous year.
That catastrophe makes Davis’s 1990 insectary startup look prescient. But Davis says, in fact, he never expected his anti-whitefly campaign would help the Imperial Valley farmers. For one thing, “There’s 500,000 acres out there. I would need, like, 100 acres of greenhouses to produce enough beneficials for everyone. In reality he d never be able to sell even the best bug to everyone - and the uncontrolled whiteflies on the fields of the holdouts would overwhelm their neighbors’ beneficials. Wandering beneficials, in contrast, would be blasted with pesticides. “Down in the desert, it’s just a chemical regimen,” Davis comments. “Every crop has a calendar spray schedule. You plant on the first of June. You spray your first herbicide on the third of June. You spray your first insecticide on the seventh of June. And then you come back every seven to ten days with that insecticide.... Everything is just based on a calendar. And it's usually successful. ’Cause it’s so hot and plants grow so fast that there’s no time to start biological control.”
Delphastus pusillus adult feeding on silverleaf whitefly nymph
Jack Kelly Clark
UC Statewide IPM Pest Project
In contrast, Davis figured that natural enemies of the whitefly might have a good chance for success in poinsettia fields worldwide (San Diego County growers produced almost $7 million worth of those plants in 1993). Poinsettias generally suffer from only one pest, the Strain B whitefly, Davis says. So if I can control that one [with a beneficial], then the growers won t need to spray at all.” Spraying hasn’t proven to be any panacea; the whitefly resists chemical attacks well and “if you spray something and it works, it may not work the next time,” according to Davis. (He says even the Imperial Valley farmers once again have had to alter their farming practices — controlling weeds better and otherwise reducing the whiteflies’ habitat, for example — since the pesticides work so poorly.)
According to Davis, the federal government also plans to impose new worker protection rules that will lengthen the interval between the time pesticides are applied and the time workers can reenter fields. Longer intervals will spell disaster for flower growers, he asserts, “Because if you’re a flower grower, you simply cannot let your plants go without intervention for more than a day or two.” Given all these pressures, the poinsettia growers should welcome any whitefly-killing beneficial that Davis can produce. So where is it?
One recent gray day, Davis led me to a greenhouse out on the Rodriguez ranch to show me the creatures on which he’s pinning so many hopes. We entered an enclosure that smelled elemental; the air was laden with water and earthiness. On benches, hundreds of plants, principally kale and collard greens, were arrayed. Davis peered among some of the leaves for a while. He spotted spiders and aphids, neither of which he wants to be harboring. “Ah, there’s one!” he exclaimed. He pointed out a tiny black dot that he assured me was Encarsia luteola.
You’d never know it without magnification, but this is a wasp. It has no stinger. But to the whitefly, it poses far more gruesome perils. The Encarsia wasp is a parasite, one of the main categories of pest enemies, distinct from the category of predators. Predatory insects kill their prey for food, and they need to eat many individuals before they reach maturity, often several per day. Much of their activity is directed toward searching for dinner. In contrast, you might say that parasites are born on the dining table; adult parasites lay their eggs in, on, or near a host. Encarsia like to inject theirs into whitefly larvae that have reached the developmental stage known as the third or fourth instars. “And they’re very picky about which ones they’ll lay their eggs in,” says Davis. They use their antennae to “drum” on the whitefly nymph, and they also walk across it in various directions. “They can tell how big it is and how healthy,” states Davis. “They can tell if it’s been infected with anything, if it’s already been parasitized, if it’s desiccating. Their children depend on the hardiness of that whitefly, and in the biological world, everybody’s picky about what happens to their kids.”
Once an Encarsia wasp finds a whitefly nymph to her liking, she’ll pierce it with her ovipositor and deposit the egg within it. But the whitefly nymph doesn’t die immediately. “The parasite wants the whitefly larva to live as long as possible,” Davis told me with a hint of ghoulish enthusiasm. “Because every day it lives, it gains more tissue mass, which gives the parasite more food.” The first thing the parasite feeds on are the developing white-fly’s reproductive organs. (“Because the whitefly’s never going to need them anyway, right?”) “Eventually, the [parasite] eats the vital organs, and that kills the whitefly.” The insult doesn’t end there; instead of abandoning the whitefly nymph’s carcass, the parasite forms its pupal case within it, thus securing an extra layer of protection while it undergoes metamorphosis. Once an adult, the wasp chews a hole in its own pupal case and then through the white-fly’s integument. “It’s like Alien,”says Davis, “an internal parasite that bursts out when it finally is done.”
After emerging, the Encarsia inflates herself, flies off, eats a bit of honeydew, then starts looking for victims in which to lay her eggs. This particular species wastes no time looking for mates. “All my parasites are females,” Davis says. “There are no males. They reproduce parthenogenetically, which means that the females lay fertile eggs, without mating. Insects pretty much have every sexual habit that’s known. I mean, they invented some!”
If you’re trying to run an insectary, and it’s costing you time and money to produce every parasite, then raising a species that needs no males (which, after all, kill no pests) is a competitive advantage. Yet it took Davis almost three years to find the Encarsia and decide to try to raise it. He says he knew that some sort of parasitic wasp would probably work best against the whitefly. “They’re much better searchers than other predators, and they can control the pests when they’re at a lower density.”
Nonetheless, there were lots of wasp candidates from which to choose. “And which one am I going to commercially produce,” Davis asks. “That’s a big question. Because if I have multiple species, it’s going to be very difficult to culture them; they’re going to interfere with each other.” Davis says he tried various candidates. “I tried to find them on my own. I tried collecting ones out in the desert.”
Finally he heard about a strain being studied by the USD A in Beltsville, Maryland. “Everyone said this was a really hot parasite,” Davis recalls. “It not only attacks the sweet potato white-fly, but it also attacks the greenhouse whitefly.” He adds that the only whitefly parasite now on the market attacks greenhouse whiteflies exclusively. So he knew that if he could grow the Beltsville strain, “I could go after that market as well as this whole market of sweet potato whitefly itself. It could be a double whammy.”
Last October, Davis managed to get about 100 of the Beltsville bugs — the Encarsia luteola. “I was very, very careful with that 100,” he says with a laugh. “I gave them a lot of food. All that they could possibly want.” Now Davis is producing something like 2000 of the wasps per day, and he’s frustrated by that quantity; he needs to increase it at least tenfold. But raising parasitic wasps — or any form of insects — isn’t like raising rabbits. In fact the two activities resemble each other about as much as playing checkers resembles playing three-dimensional chess.
Like the chess player, the insectary operator has to master three different levels of activity. While the rabbit breeder can go out and buy bunny chow to feed his animals, the would-be wasp breeder can’t turn to Petco for whiteflies. He has to cultivate them himself. Economics dictates that he also grow the plants to feed them. It’s a bit like being a lion breeder who raises sheep to feed the lions — and also has to grow the grass to feed the sheep.
Indeed, those are the terms entomologists use to refer to the three components of an insectary. In Davis’s case, the best “grass” to feed to his whiteflies would be poinsettias. He explains that another way in which the wasps are picky is that they prefer to land on the kind of plant they were born on. “So if I grow them on collards and I put them on poinsettias, they’re not going to search [for whiteflies] as thoroughly as if I grew them on poinsettias and put them on poinsettias.” Nonetheless, he says he’s been “incredibly unsuccessful” at growing poinsettias, and local poinsettia growers have declined to donate any of the plants to him. So he’s had to settle for collards and kale. Growing even those has posed challenges. “I have caterpillars that eat holes in my leaves, and I get powdery mildew. All the things that try to eat living things.” He can’t spray for those pests without killing his own sheep and lions.
Davis starts all his plants in one greenhouse; in an adjoining one he keeps his wasps in two wood-framed structures that don’t look much larger than suitcases. It seems a simple, modest operation — but one component is missing from the picture: the whiteflies. Davis has to raise them in a third greenhouse located far enough away so that any escaped wasps can’t invade easily. “It’s a continuing problem,” he says.
Within the three greenhouses, Davis’s labors are repetitive. Six days a week he loads his dusty Toyota pickup with col-lard plants he started from seed about 35 days beforehand. After seven weeks, they stand between 8 and 12 inches tall, still small enough to fit into big cardboard boxes that can be tied down in the back of the pickup. I tagged along one recent morning on the four-and-a-half-mile drive to the distant greenhouse, a former chicken coop on the ranch of some retired egg farmers, who now rent it to the entomologist. Once there, he and his sole assistant, Javier, lugged the four flats of plants inside the ramshackle structure. Davis labeled each flat with the number “130” (for the 130th day of the year), then grabbed one of the flats and motioned for me to follow him into a small inner chamber.
Here, at least in theory, all of Davis’s white-flies should begin their days. “They lay their eggs on the plants,” he explained. Before us, on the bench, stood collard plants on which the colony of adult whiteflies had been feeding for 24 hours. Here and there, among the leaves, I spotted what looked like miniature grains of rice: the mature whiteflies. Davis picked up one of the infested plants and showed how the pests clustered on the underside of the foliage. He began tapping at each of the leaves, sending a shower of the tiny white creatures onto the flat of unspoiled collard plants below it. “I try to get each plant pretty clean of adults,” Davis stated. That leaves the plant with one generation of whitefly eggs, all within 24 hours old of each other. At first I couldn’t see any of these, but Davis pointed out a coating of what looked like almost invisible hairs.
Persea mites on avocado leaf
Jack Kelly Clark
UC Statewide IPM Pest Project
Once the new collard plants have had all the adult whiteflies shaken and blown onto them, Davis leaves them in the chamber and transfers the egg-laden, adult-free plants to one of a series of long benches. Nowhere does the operation feel more like an insect factory than here. On this whitefly assembly line, each set of plants is one day older than the next, and you can walk along and observe on them most of the bug’s life cycle. “For example, how many days does it take for the whitefly egg to hatch?” Davis asked. To answer the question, he led me down the line and scrutinized what was on the plants placed there three, four, five days before. Still eggs. At the seventh day, they were just beginning to hatch, Davis showed me. At the eighth, most had done so. Davis moved farther down the line, to the plants hosting whitefly nymphs about to reach the fourth stage of their lives as larvae. “These are the plants I’m going to take back today,” he announced. Each of the biggest leaves held thousands of the nymphs, potential Encarsia cradles at their peak.
In one sense, Davis’s operation looks simple. “It’s not like designing processing chips for computers, where you have to have this enormous capital investment,” the entomologist acknowledges. Rather than capital-intensive, the work is labor-intensive. And the challenges that crop up require deep wells of inventiveness. You can’t just run down to 7-Eleven to buy insect cages or parasite collectors — alas for Davis. He says one of the biggest problems he’s having now with the wasps is collecting them; once hatched he has to get them into a bottle in order to sell them.
“Usually what you use is some biological principle. Say you wanted to trap people and people weren’t too smart. You might build a fenced-in enclosure with a door and a fan that blew out the smell of barbecue. Anyone who walked by might go in the door,, and then you’d have him. Insects are attracted to light, so one thing you can do is put them in a container and shine a light at one end. Or there are other behaviors you can try to use to make them collect themselves basically.”
Once he figures out how to make his wasps do that, Davis says he has customers lined up to buy them: researchers who want to study whether Encarsia luteola really can clobber the whiteflies that are attacking poinsettias. In the meantime, Davis recently began raising and selling a tiny ladybug called Delphastus pusillus. It eats both the greenhouse and sweet potato/Strain B whiteflies, though it works best when the pests are concentrated (and thus the ladybugs are less attractive to the growers than are the wasps). Within the past few months, Davis has begun selling the ladybugs to flower, tomato, and cucumber farmers all over the country. “They cost $25 for 100,” says Davis. “That’s a quarter apiece, pretty expensive for bugs.”
It’s the first real income his business has generated in its three-and-a-half-year life, but it’s still less than what Davis needs to support his operation. To make up the shortfall, Davis spends about half his time away from his insectary, earning money by advising local farmers on how to control their pests.
He says in some cases he has to tell them to spray their crops with chemicals. “I don’t like it, but what it comes down to is that you’ve got to save the crop or the grower goes out of business,” he explains. In other instances, Davis can recommend beneficial bugs produced by other insectaries. The choices available have expanded since he was in graduate school, he attests. “There’s now more than three times the number of species available. There’s about 35 species of insects that eat other insects available to commercial growers.” But that’s still “not that much,” Davis adds. “We need about 100 to do the job.” Getting the additional “good bugs” will require not only the kind of developmental work Davis is doing at his insectary, but also fieldwork, such as that taking place right now in the avocado orchards all over San Diego County.
A battle is raging on the leaves of those orchards and beyond — indeed, on every avocado tree in San Diego County, according to Gary Bender, the county’s farm advisor who specializes in tree crops. Bender first began to suspect that an invasion had started about four years ago, when certain homeowners in Coronado, La Jolla, and other coastal towns began sending him samples of leaves from their backyard avocado trees. Those trees looked as if they’d caught the measles; the surface of their leaves were stippled with colors ranging from mustard to purply brown. On the underside of the leaves, shiny silvery patches, slightly smaller than peppercorns, corresponded to each spot. Within those patches, Bender’s magnifying lens revealed colonies of mites.
Mites are arachnids, equipped with eight legs instead of the insect’s six. Although insects dominate the earth in terms of their sheer numbers, the arachnids outdo them in variety. Besides spiders, scorpions, and daddy longlegs, this class of animal also includes up to a million species of mites and ticks, about 30,000 of which have been named. Many of them like to eat the same plants prized by humans and thus cause billions of dollars of agricultural damage every year. The plant-eating mites have plenty of enemies, including predacious mites and a number of insects. But the newcomer to San Diego County’s avocado leaves also came equipped with a powerful defense.
What Bender and others discovered as they studied the new pest under their lenses was that the silvery patches were little nests. Unlike most plant-eating mites, these were able to spin their webbing into tightly meshed lean-tos along the veins on the underside of the leaves. Under the gauzy structures, they could settle down to the simple pleasures of phytophagous mite life: piercing the cells of the plant and sucking out the fluid; having sex; laying eggs that, magnified a few hundred times, look like pearly basketballs.
Once the plant cells under their webbing had been sucked to death, the mite colonies then disperse to other sites, to build and feast some more, leaving a trail of spotty carnage in their wake. At a concentration of about 500 mites per leaf, according to Bender, the damage was causing the leaves to fall off, exposing the developing avocados to the glare of the sun. Such exposed fruit falls off too, before maturing. The tree doesn’t die, but the attack “tends to throw the tree into a vegetative mode, instead of a fruiting mode,” Bender says — a disaster for guacamole lovers.
When the bags of avocado leaves from the anxious home-owners began piling up on Bender’s desk in the summer of 1990, the farm advisor first thought he was looking at carnage wrought by the six-spotted mite. But Bender also noted puzzling differences between that pest and the newcomer, and he sought the opinion of James McMurtry, a veteran mite specialist at UC Riverside. Although McMurtry retired a few years ago, he’s revered by growers throughout Southern California for his expertise as a field researcher, and he continues to do part-time studies funded by the state avocado commission.
McMurtry judged that the new pest wasn’t the six-spotted mite. He thought it was Oligonychus peruvianus, a relative of the avocado brown mite, but he consulted further with other acarologists at the USDA’s Beltsville laboratory. (Mite identification is an arcane process that depends upon such factors as the number and even shape of the hairs on the almost-invisible creature’s legs.) The scientists concluded that the newcomer to San Diego County was Oligonychus persea, an avocado mite that probably evolved in Mexico or Central America.
But what could be done about it? Several facts militated against a heavy chemical assault. One was the growers’ prejudice against pesticides, which Bender traces back in part to the farm advisor who preceded him. “His main mission was to tell them, ‘Don’t spray.’ ” Bender says the avocado growers, in turn, tend to be a very well-educated group, blessed with a hardy crop that always has grown in pretty much a natural state of biological control. So the growers weren’t used to either the costs or the health risks of pesticide use. Furthermore, avocado groves, often planted on hillsides, pose extraordinary challenges to anyone who wants to spray them. Spray rigs cannot negotiate some of the steep and uneven terrain. Helicopters can deliver the pesticides from overhead — but not very well to the underside of the leaves, where the vast majority of the persea mites congregate.
For these reasons, Bender says, avocado growers were receptive to the idea of using bugs to help them solve their problem, a problem that two years ago had spread to almost every commercial grove in the county. By then, McMurtry’s research held the promise of yielding a mite-y champion. In his search for predators of the six-spotted mite, McMurtry five or six years ago had imported a predatory mite from Florida named Galendromus helveolus, and he decided to test it out against the persea menace. In early 1992, he and his longtime assistant, Horace Johnson, released the helveolus in a number of persea-infested trees in San Diego County. When they checked back a few weeks later, they were encouraged by what they saw. “The helveolus was reproducing, building up to pretty high populations. And the persea population seemed to be lower than it was in trees where we hadn’t released the predator,” McMurtry says.
One drizzly morning, I made the drive up to McMurtry’s bastion on the UC Riverside campus. Though the professor was absent, Horace Johnson welcomed me warmly. Now 72, Johnson first began working on this campus in 1945 and has been employed here for the past 38 years. A courtly man with a robust sense of humor, Johnson led me out in back of the Mission-style entomology building. In a low outbuilding, we made our way through a corridor to a tomb-like inner chamber crammed with teeny killers.
Here McMurtry has brought together predacious mites from such far-flung parts as Jordan, Israel, Morocco, Mexico. Each lives within its own wooden box into which one or two screened portholes admits air. Johnson opened one of the boxes and pulled from its recesses a square, shallow metal pan about the size of his hand. It held a water-logged sponge in which a tile had been set. In the very center of the tile, no more than two inches square, flourished a colony of creatures so small that they seemed like geometric points — alive and moving, but dimensionless.
Johnson made me look at one species after another under a microscope, which revealed the inaccuracy of that perception. I could see their curved little legs, their complex mouth parts, their plump bodies, each species distinctive—or so Johnson assured me. Even without a microscope, he can recognize most of them; decades of experience have empowered him to see shapes, textures, colors in the dots. “I can also tell which they are from the way they walk, the way they move,” he told me. “These guys are like my family, almost.”
When he returns from vacations, Johnson fumes over the way his charges have been tended. “They always overfeed them! Not like me. I make them eat everything that’s there. They’re usually pretty hungry by the time I feed them. They’re standing up on their hind legs and waiting for me!” He’s joking, but serious about not wasting the predator food.
Most of predacious mites in this lab eat the dried eggs of a plant-eater known as the Pacific mite; Johnson raises them on lima bean plants in a steamy greenhouse on another side of the entomology building. Like Jim Davis’s operation, it’s a tedious process, and it’s easy to imagine not wanting to waste the output. Even the helveolus predator, which likes to eat persea mites, can survive on the Pacific mite eggs, though Johnson commented that the helveolus has been the most difficult of all the thousands of predacious mites he’s ever reared over the years.
He sounded as if he was glad he didn’t have to raise commercial quantities of them. The university doesn’t do that with any mites; its scientists study the bugs and then allow others to exploit their economic potential. In the case of the helveolus, once McMurtry and Johnson had decided that it looked like a good potential controller of the persea pest, the task of growing it in large numbers fell to a pair of former UC Riverside lab technicians, Glenn Scriven and Walt White.
Their Riverside company, Biotactics, boasts that it produces the largest selection of predatory mites in the United States. It started back in 1970 as a “weekend business,” according to the two partners. Scriven and White began raising Phytoseiulus persimilis, a bright orange mite native to the tropics of South America, with an eye toward selling it to Southern California rhubarb farmers. “They had gotten themselves into a terrible problem with overuse of chemicals,” Scriven explains. “They were just dumping on anything they could get their hands on, but within weeks the pests would return again.” Desperate for help, the farmers decided to try out the mites. “Initially, it looked totally hopeless. But within a few months, it was just like a miracle.”
Scriven and White’s enterprise remained confined to their back yards for many years, while they continued to work at the university. Then around 1987, California strawberry growers faced catastrophe in the form of a federal ban on one of their primary pesticides. To the growers’ rescue came the persimilis mite, which was a substantial help in controlling the spider mite pest. Scriven and White suddenly found themselves overwhelmed with demand. That’s when they quit their jobs and built greenhouses to grow the persimilis mites on a grand scale. While in 1987 they had sold 862,000 of them, in 1989 they sold about 52 million. It’s now standard procedure for strawberry farmers to fortify their young plantings with the tiny predators.
Biological Photography, Moreno Valley
Since then, Scriven and White have expanded in other directions, and they now sell about eight different types of beneficials, including Galendromus helveolus, the would-be avocado tree defender. It is tough to culture, they concur. “It was six months before we really made any progress with it,” says White. Biotactics started selling it around October of 1992, and today the company is making all it can — roughly two million helveolus per month. Yet that’s still not enough to meet the demand during the summer months, when persea populations skyrocket.
Last year the supply of helveolus was only sufficient to place colonies in about 5000 of the 25,000 to 30,000 acres of avocados then planted in San Diego County, according to Rick Marrocco. Marrocco was involved in that dispersal; his Fall-brook Agricultural Lab is one of the few retail sources for the helveolus mite. (Jim Davis’s American Insectaries is one of the others.) Like Davis, Marrocco has a master’s degree in pest management from UC Riverside, and these days he spends even more time than Davis does tromping through local avocado groves, trying to assess how the war against the persea mite is going.
One day last month, I joined Marrocco in a Pauma Valley grove that seemed as if it ought to have enjoyed a clear success by now. This grove isn’t huge — 25 acres that were planted 20 years ago by a former carpet wholesaler named Ray (he asked that his last name not be used). By Marrocco’s account, Ray is a paragon: intelligent, hard-working, and always open to new ideas about farming. At the beginning of 1993, Marrocco says he would have judged Ray’s grove to be one of the healthiest in the North County — well-watered and nourished, and blessed with a “marvelous” fruit set last spring. But by then, Marrocco knew that even the strongest groves weren’t immune to the persea damage, so he urged Ray to help protect himself by releasing some helveolus mites. Ray agreed; the helveolus, though expensive compared to most beneficials, costs less than pesticides (about $80 an acre for the bugs, as opposed to between $100 to $400 an acre for the chemicals).
In April of 1993, Marrocco moved through Ray’s grove, stapling brown paper bags to clusters of leaves on every other tree. Each bag contained a teaspoon or two of the sandy-looking mix produced by Biotactics — a combination of helveolus mites, ground dried corn cobs, and dried Pacific mite eggs (to sustain the helveolus, which otherwise turn cannibalistic).
Marrocco looks back on that action and says he wasn’t counting on a miracle. While the helveolus mites had proven to McMurtry’s and Johnson’s satisfaction that they are able to penetrate the persea nests, the pests have another advantage over their predators — an awe-inspiring ability to travel. Marrocco says you can see it in action on certain mornings, in heavily infested groves. “About 6:00 or 7:00 in the morning, when the sun warms up the ground, you’ll get a little inversion — like what gets the buzzards off the ground,” he says. “Apparently the [persea] know exactly when it’s perfect. And boom! They spin little webs. And then you’ll see them leave by the billions. You stand there, and you catch the light, and you’ll see the tree with just millions of webs hovering around it. It’s really bizarre—though they’re so small most people don’t ever notice it.”
The helveolus, in contrast, don’t spin the webs, so they spread from tree to tree much more slowly, slow enough for McMurtry to warn that the helveolus might take as long as three or four years to get the better of the persea. Despite that warning, Marrocco says he was heartsick at the sight of what he found in Ray’s grove by the middle of last summer. The persea population was exploding; and while the helveolus mite had multiplied, “it just wasn’t significant enough,” Marrocco says. Rather than watch Ray’s entire crop drop off the trees, along with all the leaves, Marrocco recommended spraying the trees with a insecticidal oil.
“Spraying to me is a last resort,” Marrocco told me. He says he was educated to be a biological control person at the university, and long before that, insects entranced him. “As a kid, I was a 4-H entomologist, and I chased reptiles and insects all the way down to Guatemala when I was in junior high school.” Insecticides, he states, “are a dead end. Because you kill everything off and you’ve got to start over, and typically what happens is that the pest usually comes back much, much quicker than the beneficial.” However, an insecticide applied during an acute crisis can buy a grower time to get his crop to market, Marrocco asserts. “You kind of shoot yourself in the foot with spraying, but you’ve got to have the cash flow or you’re out of business.”
Ray wound up spending about $6000 for the single application of oil last summer. Despite that, most of Ray’s new fruit dropped off, and the surviving crop brought only 15 cents a pound, a disaster that put Ray at least $30,000 behind for the year. This spring, Ray’s trees had “set” only about 17 percent of the fruit set last year, and Marrocco told me it was imperative that Ray be able to harvest and sell it all. For that reason, Marrocco was visiting the grove every week or two, trying to make the agonizing call as to whether more spraying would be necessary.
On the day of our visit, we parked near the road, then started climbing up the steep hillside. To my eyes, the trees covering the incline appeared radiant in their new foliage, a light green blushed with bronze. Most of the old, spotted leaves had fallen off and they crunched underfoot whenever we took a step. Whenever we paused, the steady hum of bees floated down from somewhere high overhead, “This is a neat environment, isn’t it?” Marrocco asked. “There are not a lot of bugs in an avocado grove, and it’s kind of a real mellow, subtropical environment.” He was smiling, appreciative.
The smile faded when he started plucking leaves from the trees and studying them. “I’d say there are 50 to 70 bad guys on this one,” he muttered. “And I see one, two...three good guys.” Once again, the effect of experience upon eyesight astonished me. While I glanced and saw nothing, Marrocco saw bodies that he explained to me were “lightbulb-shaped.” These particular good guys weren’t the helveolus that he had released in the grove again around March of this year. Instead they were Amblyseius hibisci— yet another predatory mite that has lived in California avocado groves for a long time. Pitted against the persea, it has the disadvantage of not being able to penetrate the persea webbing. But it will attack free-roaming persea. Now Marrocco was delighted to see it out in force. “There were hardly any on these particular trees last year,” he explained. Perhaps with its numbers booming, it would help control the plague.
As we moved deeper into the grove, he kept finding hibisci, but also a depressing quantity of the persea — up to 200 on some leaves. “If it gets to 250 bad mites and I don’t have a complement of good mites, then we’re going to spray,” Marrocco muttered. He plucked another leaf and exclaimed, “Now look at this! The beneficials are tremendous.” He counted 13 hibisci. “Why so many there?” he asked. “Who knows? That’s nature.”
Marrocco did find a few of the helveolus mites, but he walked away stymied by the mysteries of what was going on. Were there colonies of helveolus concentrated in the tops of the trees, as one agricultural observer had suggested? Would they move down when the weather warmed and the persea population exploded? Would the Amblyseius hibisci, which eats avocado pollen, die off now that the pollen was disappearing? At the moment, Marrocco judged that the grove had a 50-50 chance of being sprayed. “It’ll just have to be wait-and-see,” he told me. He would evaluate the ranch again in a few more weeks and hope to find out, “Who’s going to make the first move? I wish I could see more of the cards now.... This grove is in an absolutely precarious position.”
I checked back with Marrocco on June 9, and he told me that the beneficials were continuing to keep pace with the pests well enough so that he still hadn’t recommended spraying Ray’s trees. “We’ll have to continue to watch it week by week.” Marrocco doesn’t doubt that biological control will work in local avocado groves. “Besides the predatory mites, there are little midges that feed on the persea. There’s a little stethorus beetle that feeds on it. There’s little thrips. There’s lacewings.” All these insects aren’t very efficient, Marrocco concedes, because they can’t invade the persea nests the way the helveolus can. “But they will eat the persea mite, and it’s all going to help. Plus, the helveolus is going to evolve. You put a lot of food out there, and eventually the system is going to go under biological control.”
That’s an opinion echoed by Jim Davis, up at his North County insectary. He says he’s “extremely optimistic” not only that ecological balance will return to the avocado groves, but that biological pest control will come to supplant the chemicals that have dominated American agriculture for the past 50 years. Although insect sales only amount to about 1 percent of the total pest-control market, “What that says is that this hasn’t yet come of age,” Davis says. “But ten years ago, those insect sales were probably a tenth of what they are today. The trend is up pretty steeply, especially when you consider the economy.”
Davis says he sees more and more references to sustainable agriculture in the farm journals. More and more growers are experimenting and enjoying successes. And the ranks of the experimenters are no longer confined to small-timers on the. fringe. “Some Of The State’s Major Growers Have Gone Organic,” read one front-page story last August in the Los Angeles Times. It reported that the giant table-grape grower, Pandol and Sons, has cut their chemical use by 70 percent; Dole Food and Gallo Wines also rank among the recent converts.
“It makes more sense ecologically — but that’s not going to drive [the change from pesticides to beneficial bugs],” Davis asserts. “It’s just becoming too expensive to develop new pesticides. It now costs between $30 million and $50 million to bring a new pesticide to market But with even the new pesticides, which they hoped would last for 20 years, they’re finding resistance in the pests after only a few years. The real driving force is biology. They can’t produce the pesticides as fast as the pests can become resistant.”