When Dan Bean and Tom Dudley were high school classmates in Southern California, their biology teacher offered extra credit for eating oddities of scientific interest. The duo dove into the challenge - Bean, a quiet man with a slow grin, allows that sea-urchin gonads were much tastier than he expected - and their combined score shamed all competitors. Which may partly explain why, on a clear fall day more than three decades later, Bean and Dudley are driving a rocky red dirt road on the Utah-Colorado border, on their way to watch a beetle kill some weeds.
"What about here, Doctor Bean?" teases Dudley, pointing out the truck window at a tangle of riverside trees and shrubs. Dudley, now a trim, sharp-featured ecologist from the University of California at Santa Barbara, is visiting his friend and colleague Bean, an entomologist at the Colorado Department of Agriculture insectary in nearby Palisade. Bean parks his white pickup and the pair clambers out, grabbing long, cone-shaped cloth nets as they head toward the trees.
After a few moments of net-swinging, Dudley shouts from the thicket. "Here's one ... one, two, three, four."
Bean and Dudley are searching for Diorhabda elongata, familiarly known as the tamarisk leaf beetle, newly arrived here from Kazakhstan by way of Utah, and, as it happens, stenciled in larger-than-life size on Dudley's T-shirt. First released in the United States in 2001, the beetles were set free in Utah, about 20 miles from this spot, in 2005, and recently began to march along the muddy waters of the Dolores River. Their target, as their name indicates, is the riverside shrub known as tamarisk or saltcedar, one of the most infamous invasive weeds in the West.
Six weeks ago, Bean says, there were no beetles in this particularly thick stand of tamarisk, cottonwood, and willow, but now, the tamarisk - which towers, treelike, over the scientists' heads - displays light brown tips, one of the first signs of beetle attack.
"The natives are already here," Dudley observes, looking at the native cottonwoods, some tall enough to form a canopy over the weeds. "They just need to be freed up." "And the beetles are going to free them," says Bean.
But their cheer is momentary. Though Diorhabda is a powerful weapon against tamarisk, it's a very complicated one. "Whenever anyone thinks they have a silver bullet," says Dudley, again diving into the brush, "it usually turns out to be a sort of off-gray color."
Tamarisk is one of the lessons in American West 101: About the time newcomers learn that the striking black-and-white bird on their porch is a common magpie, they find out that the feathery green riverside shrub with the pretty pink sprays of flowers is actually a nasty weed.
When and exactly how it arrived here is a matter of some debate, but the usual story is that tamarisk, a Eurasian species, was first planted in the West in the mid-1800s, both as an ornament and for erosion control on railroad beds and elsewhere. By the late 1800s, it had naturalized, and by the 1960s, it dominated vegetation along the Colorado, Rio Grande and Pecos rivers. Today, its Western range stretches from northern Mexico to Montana, and from Kansas to California, and covers over 1 million acres.
The conventional wisdom is that tamarisk, with its deep, tenacious root system, sucks up much more water than its native neighbors. Reality, as usual, is more complex: Recent analyses by researchers at the University of California at Santa Cruz show that in the drier areas atop riverbanks, tamarisk does use far more water than native plants. In wetter areas near streams, stands of cottonwoods and willows often use nearly as much water as their exotic competitor.
Yet there's no shortage of reasons to dislike tamarisk. Even though it offers some substitute food and shelter to native wildlife - a point we'll tackle later - research shows that in general, animals living in tamarisk are less diverse, fewer in number, and less healthy than their counterparts in native vegetation. The plant's trademark dense growth is thought to increase fire risk along riverbanks, and it resprouts quickly after burns. And as any boater can attest, the weed narrows streams and rivers, and chokes out campsites.
Since the 1960s, Westerners have worked to rid the region's rivers of tamarisk, hoping to salvage scarce water, protect wildlife, or fend off wildfire. Millions of dollars, and countless backbreaking hours, are spent each year on efforts to hack down and poison the plants. Perhaps the most ambitious project is headed by The Nature Conservancy, which has spent $600,000 removing tamarisk from the San Miguel River in southwestern Colorado. Over the past seven years, volunteers and contractors have used chainsaws, clippers, heavy equipment and herbicides to rid the watershed of the weed; they've covered 80 miles of the river and its tributaries so far, and organizers are happy to report a resurgence in native plants. They plan to complete the remaining 10 river miles in just over a year and use periodic, much less intensive retreatments to keep the watershed nearly tamarisk-free.
Along the Rio Grande and its tributaries in New Mexico, state-funded aerial herbicide spraying has killed tamarisk on thousands of acres, and on the Middle Rio Grande, heavy machinery has plucked the plant from the Bosque del Apache National Wildlife Refuge. On a long-neglected stretch of the lower Colorado River near the Mexican border, the city of Yuma, Ariz., and the neighboring Quechan Tribe have collaborated on a campaign to clear tamarisk and other invasive plants from the banks.
Near Grand Junction, Colo., a nonprofit group called the Tamarisk Coalition recruits volunteers to cut the plants out of a wilderness area near Colorado National Monument. The wilderness designation limits workers to handsaws, "and sometimes you feel like you're out there with a toothpick," says coalition staffer Clark Tate. But there are advantages to the group outings, she adds: "We have matched up some very happy couples."
Despite their successes, these intensive efforts can be reversed with just a few years of subsequent neglect, and are difficult - if not impossible - to execute on a regional scale. "There's just not enough money to get rid of it all with chemicals and bulldozers," says Dudley. Broader, lasting success, say many, requires reinforcements, preferably numbering in the millions, preferably willing to work for free. That's where biological control, in the form of Diorhabda elongata, comes in.
"Biological control is very risky," acknowledges Ruth Hufbauer, an invasive-species researcher at Colorado State University. "Yet when it's done carefully, done well, it's an incredibly powerful tool. It shouldn't be dismissed out of hand."
For a decade, Jack DeLoach searched for a worthy tamarisk adversary. DeLoach, a U.S. Department of Agriculture entomologist, has traveled to Israel, southern France, China, Kazakhstan and Turkmenistan, doing what is somewhat romantically known in the biocontrol business as "foreign exploration."
In his quest for a natural enemy for tamarisk, he teamed up with local entomologists to collect beetles from the weed's native range, sifting through the several hundred species known to attack the plant. He and other researchers tested about 20 species overseas, and brought about half back to his lab in Temple, Texas, for further research, finally whittling the possibilities down to one: Diorhabda.
Most important to biocontrol researchers - and their regulators - is that the insects they release have very particular tastes, proven to attack nothing but the weed in question (God forbid they eat food crops). Biocontrol researchers say that, in this respect, their profession has a clean record, and some dramatic successes to its credit. In the 1940s, when the introduced Klamath weed beetle decimated a rangeland weed in Northern California and southern Oregon, grateful ranchers and farmers in Humboldt County, Calif., even honored the insect with a commemorative plaque.
The most commonly cited biocontrol "mistake" in the United States, the 1960s introduction of a weevil that eats native as well as introduced species of thistles, was simply a product of its times: Researchers say that scientists and regulators knew the weevil's tastes, but thought native thistles weren't worth protecting. "Nobody would approve a release like that today," says Hufbauer.
The U.S. Department of Agriculture, advised by representatives of other federal agencies, now authorizes biocontrol insects for both agricultural weeds and ecological plagues. The numerous targets include leafy spurge in the Northern Plains and elsewhere, the invasive evergreen melaleuca tree in Florida, and several species of knapweed.