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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?

WE'VE BEEN DRIVING south from Missoula, Montana, for nearly an hour on a torrid August afternoon when Noah Poritz veers his tomato-red pickup truck onto the shoulder of a gravel road and slams on the brakes. The tires slide to an abrupt stop, churning up a cloud of hot dust. Poritz leaps out and surveys the stark landscape. "This is the site," he declares, making a long, slow sweep across the horizon with his hand. We're in the heart of the Bitterroot Valley, a 100-mile-long patchwork of dairy farms and cattle ranches, flanked by massive granite peaks. "It is perfect weevil weather today," says Poritz. "They can't handle the heat of the soil. When the temperature rises, they climb the plants. When it gets hot is when we scoop them up."

Poritz is a 52-year-old entomologist who earns his living selling beneficial bugs: critters that munch on invasive pests but leave native flora and fauna alone. Known as biological control, or biocontrol, it's akin to the age-old trick of scattering live ladybugs on flowerbeds to consume aphids. But there is a key difference: Ladybugs are a temporary fix to rein in a seasonal pest. Poritz targets long-term infestations by invasive organisms. In their native habitats, all weeds and insects have natural enemies that prevent them from becoming pests. But when a species is inadvertently transported to our shores, it leaves its predators behind. Biocontrol reunites predator and prey.

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Not only do these beneficial bugs keep harmful pesticides out of sensitive ecosystems, but they're often cheaper than spraying. Depending on the type of pesticide your pest might require, you could spend between $2,000 and $30,000 annually to spray a 100-acre tract. But for that same size lot, $100 worth of beneficial bugs could do the trick, and they'd reproduce indefinitely, subduing pests year after year at no further cost. Most importantly, biocontrol can work on "low value" land—acreage where it's not cost-effective or feasible to spray.

Poritz was a technician with the USDA's Agricultural Research Service when he launched his company with his wife Leona in 1986. "I couldn't sell any of the insects I worked with if I wanted to move up the career ladder," he recalls. "So I quit." Today, Poritz is a leading supplier of weed-killing biocontrol insects—selling more than a dozen insects that combat a variety of invasive plants, such as tansy ragwort, toadflax, leafy spurge, and purple loosestrife.

I've come to the Bitterroot Valley to help him collect knapweed root weevils, half-inch-long beetles that originate in Europe and eat only spotted knapweed, an invasive plant indigenous to Eurasia. Because spotted knapweed has no natural predators in the United States, it infests rangelands and marginalizes native grasses that feed wildlife such as elk, deer, antelope, and bison—displacing up to 90 percent of their winter forage—as well as cattle. For every acre that's infested, ranchers lose about $16 (PDF) in potential income. On wildlands, the damage is roughly $6 per acre.

Spotted knapweed is just one of more than a thousand invasive weeds and bugs in the US. The first likely arrived with early European settlers, but thanks to the global economy, with its airfreight and container ships, their number is rising exponentially. Weed infestations are increasing by 14 percent annually, spreading into Western national parks, forests, and wildlife refuges at a rate of 4,600 acres a day. Invasive pests are jeopardizing nearly half of all species listed as threatened or endangered (PDF). By 2004, a study published in the journal Ecological Economics put damages from weeds and insects alone at $54.6 billion a year (PDF), about half as much as we spend annually on the war in Afghanistan.

Right now, beneficial bugs are at work on roughly 100 million acres of weed-infested land in the US, an area about the size of California. To treat that same acreage would take anywhere from 600,000 to 6 million gallons of herbicides and require multiple doses over consecutive years. There are also dozens of biocontrol programs underway where bug-eating bugs feast on invasive insects.

Poritz yanks a knapweed plant from the ground and snaps open its root. "The root weevil attacks the central taproot," he explains. "You can crack open those roots and see where they did their damage." We're at a 40-acre ranch smothered in knapweed, its violet flowers casting a purple glow across undulating fields. Knapweed root weevils were introduced to the Bitterroot years ago to control the plant, but Poritz says there are more than enough to eventually quash the weed, which is why the landowner gives him permission to harvest the surplus bugs.

For all the talk of a weevil explosion, I'd been expecting something biblical. But my untrained eyes don't see any weevils. Just then, Poritz plucks one from the top of a wooden fencepost, where it had been sunning itself. "It's a big honkin' weevil!" he exclaims. "It's my favorite bug." He deposits it in the palm of my left hand. The root weevil is sand-colored and shaped like a kidney bean, with brown spots and a protrusive snout suggestive of an anteater. Exquisite camouflage had rendered it invisible until Poritz showed me what to look for. Suddenly, we are in Weevilville.

Poritz hands me an oversize metal-rimmed net that he engineered with the help of a friend who has a machine shop, and then he demonstrates his sweep-and-scoop weevil-catching technique, which makes him look like he's dancing a waltz. We slather on sunscreen and don matching wide-brimmed khaki sun hats. The work is mindless and repetitive. Poritz listens to his iPod while trudging through waist-high knapweed and making long, repetitive arcs with his net. In less than an hour, my forearms and back are throbbing. Poritz tells me he was once hospitalized and given intravenous steroids for a "severe allergic reaction and extreme asthma," possibly triggered by pollen inhaled while collecting and sorting bugs. Today, he's sniffling and congested after just a few hours of netting weevils.

Because the pickings are ripe, Poritz insists we push through until sunset. A collective cry soon shatters the silence: the high-pitched whine of grasshoppers rubbing their wings together that escalates with the soaring late-afternoon temperatures. After a few clumsy swoops, I empty the contents of my net into a queen-size pillowcase that Poritz had given me earlier. The plump sack hisses and pops, like a wet log tossed onto a roaring campfire. I peek inside, careful not to let any critters escape. It's a writhing, wiggling bug orgy. An entire root-weevil clan is marching single-file up the inside of the pillowcase, determined to liberate itself from bondage. There are heaps of grasshoppers, too, plus ants, bees, gnats, gall flies, stink bugs, and wasps. My skin starts to itch, a purely psychosomatic response. And then there's the smell, familiar yet kind of gross: a robust bouquet of freshly cut cucumber with musky overtones.

Two days later, we've collected 40,000 root weevils, which Noah Poritz will sell. The going rate is 75 cents a bug.

Full pillowcases are stuffed into a portable electric beer cooler that plugs into the battery of Poritz's truck. Chilling the weevils ensures they stay alive until we reach his sorting facility. It's four hours southeast in Bozeman, where he lives in a placid suburb about two miles from his bug shop. A clever vacuum system of screens, fans, and hoses lets him separate beneficial insects from benign bugs, which he sets free. His wife pitches in, doing a final inspection by hand. Poritz thinks our two-day haul in the Bitterroot Valley has reaped 40,000 root weevils. The going rate is 75 cents a bug. He accepts orders online and ships overnight. A hundred weevils are sufficient to start a colony big enough to contain a local knapweed outbreak. "We provide ranchers, county agents, and state and federal land managers an alternative to herbicides," he says, "and the results are dramatic."

 

HISTORIANS HAVE traced some of the earliest known attempts at biocontrol to the Chinese, who dispersed ants into mandarin groves to devour stink bugs and caterpillars in the fourth century. Mauritius was first to enlist a non-native organism: In 1762, the French colony imported mynah birds from India to eat locusts. But most credit a London-born entomologist named Charles Valentine Riley, who was appointed chief of what is now the USDA's Division of Entomology in 1881, with spawning the modern biocontrol movement.

Around that time, an invasive insect called cottony cushion scale piggybacked on imported acacia saplings from its native habitat in Australia to Southern California, where it assaulted hundreds of thousands of orange trees, decimating the burgeoning citrus industry. In 1888, Riley dispatched a colleague to Australia, instructing him to track down any insects that preyed on cottony cushion scale. He returned with the vedalia beetle, a type of ladybug. Not long after, the USDA released vedalia beetles into California's orange groves, and within a year they'd crushed the cottony cushion scale.

Nobody is exactly sure how spotted knapweed got to the Bitterroot. One theory blames Eastern European immigrants, who in the mid-1800s might have transported its seeds in containers of alfalfa. But it could have come over to America in the soil ballast of sailing ships, which was dumped upon arrival in port to make room for export cargo.

In any case, it took half a century for spotted knapweed to reach the Intermountain West, where the climate and soil conditions—and a lack of natural predators—let it flourish. By the mid-1970s, spotted knapweed blanketed 4 million acres of western Montana. An ad hoc team of scientists—from Montana State University, the Oregon Department of Agriculture, the University of Idaho, Washington State University, Agriculture and Agri-Food Canada, the USDA, and CABI, a nonprofit research lab based in Switzerland—joined forces to fight the invasion. Botanists knew that knapweed was native to Eurasia, where it was kept in check by a variety of bugs. In 1984, a group of entomologists went there to find out if any of them were "host-specific"—that is, ate nothing but knapweed.

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