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Alien vs. Predator: Biocontrol Edition

Can an imported weevil KO an invasive weed that's choking out our parks and pastures? Or do we enlist bugs at our own peril?

Jim Story, a retired research entomologist from Montana State University and the country's preeminent spotted knapweed expert, was on the team. He and his colleagues spent five years investigating knapweed feeders in Europe and at quarantined labs back in the States. They had to be very careful. "You certainly wouldn't want something that feeds on knapweed but turns out later to feed on alfalfa and bananas and barley and everything else," he says. They evaluated 15 bugs. The winner was the root weevil, because it was the biggest host-specific bug that attacked the plant at its core. In 1988, Story's group released the first knapweed root weevils in Montana, a batch of 50 adults.

"You certainly wouldn't want something that feeds on knapweed but turns out later to feed on alfalfa and bananas and barley and everything else."

"By 2004, the knapweed had collapsed because the insect had hammered it so hard," recalls Story. But the weed is still common—part of the reason Poritz is able to stay in business—and knapweed varieties still cost Montana tens of millions of dollars (PDF) a year in land-degradation losses and declines in agriculture and livestock revenues. Story explains: "A 20-year timeline is pretty normal. I truly didn't know when I started back in '74 that I would see any results during my career." Biocontrol programs are a home run a quarter of the time and flop about as often. The other 50 percent show mixed success. But while a winning biocontrol program can take a generation or two to gain a foothold, when it does, its efficacy is virtually guaranteed as its costs wane. "Once the insects are released, they multiply and spread and survive from year to year, providing perpetual control," says Lincoln Smith, an exotic and invasive weeds research entomologist with the USDA's Agricultural Research Service.

Chemical mitigation boasts no such advantage. Smith adds, "If you spray a plant, there are seeds in the soil. And those seeds last a long time. So you kill all the plants, and you come back next year, and there are more plants. You need to do that at least three years, and follow up every year. If one plant survives, it's going to produce enough seed to re-infest your whole field."

Some insects can mount a resistance to pesticides in fewer than two years, prompting chemical companies to concoct increasingly potent sprays, which leads to ever-more resistant bugs. "Each generation of insecticides is more specific, more expensive, and more difficult to use," says Norman Leppla, an entomology professor at the University of Florida. "You also have to apply insecticide continually. There is no long-term benefit. It doesn't matter where you look—environment, climate, production agriculture—we've reached the end of our chemical rope."

It's harder to gauge the square-mile impact of invasive bugs because they're peripatetic and seasonal, but they can be just as problematic. Take the emerald ash borer, a small beetle with shimmering green thorax armor. "It came from China on crates," says Roy Van Driesche, an entomologist at the University of Massachusetts-Amherst, who has coauthored two books on biocontrol. "[It] is killing tens of millions of trees in the Midwest and will soon be nationwide if we don't find biocontrol agents to lower its density and slow its spread."

A typical biocontrol program targeting a single pest can cost up to $750,000 a year. Yet—even as invasive weeds are spreading at the aforementioned rate of 14 percent a year—total federal spending against invasives, of which biocontrol is a small part, has flatlined at $1.2 billion. Meanwhile, the big players of the $40 billion global pesticide industry—Dow, Bayer, Syngenta, BASF, and Monsanto—"are able to exert tremendous control through allies in universities, the USDA, through Congress, and through their public relations efforts," says Poritz.

Biocontrol can be a tough sell, not only because of the uncertain outcome and long time frame, but because the cost is all up front. But Van Driesche says that calculus is "pretty insensitive to the number of acres that ultimately benefit. Let's say you spend $5 million over 10 years to run a project. If the [biocontrol] release infests 1 million acres, then the cost per acre is $5." That's a pittance, compared with pesticides at potentially hundreds of dollars per acre. And biocontrol is essentially free once the beneficial bug establishes itself. One study cites a 23-to-1 benefit-to-cost ratio, even including failed projects. But it does take time—5 to 20 years per project, Van Driesche points out: "There is no way to do a crash project of biocontrol."

 

THE ROOT WEEVIL assault on Montana's spotted knapweed epidemic is an exemplary success and, in terms of acreage, is one of the largest applications of biocontrol in US history. But biocontrol has also begun to rein in the alfalfa weevil and screwworm fly. Chrysolina quadrigemina, a beetle intentionally imported from Australia in the 1940s, has battled Klamath weed (a.k.a. St. John's wort), which poisons cattle and threatened to wipe out California livestock in the 1930s (PDF). In Texas, the phorid fly is preying on South American fire ants. The Mediterranean yellow starthistle—the most insidious weed in California, where it attacks orchards and vineyards—is up against several species of weevils and fruit flies imported from its homeland. A South American planthopper is targeting water hyacinth, which lowers oxygen levels, causing fish to go belly up.

Biocontrol isn't without risk. "The biggest mistakes were made by farmers and plantation owners in the 1700s and 1800s who introduced various predacious vertebrates like the mongoose to control rats, which was very damaging to native birds and lizards," Van Driesche recalls. (Today, the USDA mandates that any imported biocontrol insect must be shown to eat only pests.) A more recent snafu (PDF) occurred when scientists tried to combat spotted knapweed with a fly that laid its eggs inside the knapweed seeds, destroying them. The fly proliferated and became a favorite meal to deer mice. Soon, an overpopulation of deer mice attracted owls, which preyed on the rodents and eventually excreted the seeds in their pellets. The owls became a transport mechanism for spreading knapweed. And when scientists employed an Asian leaf beetle to take on the Eurasian saltcedar—which concentrates salt, poisons everything in its shadow, and has infested more than a million acres and 56 national wildlife refuges—the beetle became too successful, threatening the habitat of the endangered Southwestern willow flycatcher.

And biocontrol isn't feasible for every pest. If an invasive weed is closely related to a native plant, it's nearly impossible to find a bug that attacks the pest but not its kin. Other drawbacks are climate and topography: A beneficial bug that excels in Florida may founder in the Southwest, even though its target weed or insect thrives with impunity. Sometimes the population of the beneficial bug stabilizes at too low a level to mitigate the spread of a weed. This happened when the Hyles euphorbiae, a pink-hued hawk moth, was introduced in the 1960s to combat leafy spurge, a Eurasian perennial now present in 19 states and seven national parks. Biocontrol teams have since had to import 13 other insects to join the hawk moth—though the coalition force is making progress against leafy spurge, reducing infestations by up to 90 percent.

Consider the stowaway weevil in my luggage: invasive insects may not morph into superbugs, but biocontrol isn't risk-free.

Fortunately, as biocontrol bugs are introduced to new ecosystems, they don't appear to suddenly develop cravings for other kinds of plants or insects. Nor do they jump species—like mad cow disease or the virus that causes swine flu—or morph into some kind of superbug. "They have evolved over eons of time with their host weed, so the likelihood of them deviating is extremely small," Story assures me.

Still, adaptation works in mysterious ways. Take our old friend the root weevil. In many places, it has vanquished spotted knapweed only to see it replaced by an invasive known as cheatgrass. This is a fairly common problem: Established invaders like spotted knapweed have already wiped out native plants, so biocontrol creates a vacuum often filled by other invasive plants. In other words, it's hard to put the genie back in the bottle.

I'm confronted with this when, while unpacking my suitcase after returning from my trip with Poritz, I discover a souvenir from my travels: a perfectly intact root weevil clinging to the leg of a pair of blue jeans. The feisty stowaway rears on its hind legs and flails its forward pincers in the air in a menacing fashion, like a boxer throwing jabs. It's a reminder that insects and weeds are wily vagabonds that can transport themselves across oceans and continents with consequences nobody, not even well-intentioned entomologists, can quite anticipate. "By distributing millions of insects, I am having a macro-impact on the environment," says Poritz. "You can literally watch a landscape transform after doing biocontrol. It's not exactly Charles Darwin and the Beagle, but what I do is natural history."

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