Berkeley - One of the West's most noxious wildland pests, an alien tree called saltcedar that invades riverbanks, pushes out native willows, chokes streams and impoverishes riparian habitat, is about to get the unwanted attention of a very hungry bug.
On Tuesday, May 22, a team of biologists from the University of California, Berkeley, and the U.S. Department of Agriculture's Agricultural Research Service (ARS) in Albany, Calif., will release in a patch of saltcedar trees in California's Owens Valley a small black-and-yellow striped beetle that loves to munch saltcedar for breakfast, lunch and dinner.
The biologists, working with the Inyo Co. Water Department, hope that the bug, a leaf beetle imported from the saltcedar's native habitat in central Asia, will help control the tree and perhaps eliminate it from many of the rivers it has invaded.
"We hope that the beetle and a leafhopper that already lives on the trees will give saltcedar a one-two punch to knock it out," said ecologist Tom L. Dudley, a UC Berkeley researcher in the Department of Integrative Biology, College of Letters & Science, and head of the vegetation monitoring section of a saltcedar control consortium involving eight Western states.
The beetle is one of only a handful of natural enemies released in biological control programs to control wildland weeds, compared to more than 110 targeting agricultural plant pests, Dudley said. Most releases also have targeted herbaceous plants, not woody plants like saltcedar.
"The goal here is to protect environmental values and wildlife ecosystems," Dudley said.
Other members of the consortium released the beetle last week in a stand of saltcedar in Colorado, and more releases are planned in coming weeks in Nevada, Wyoming, Utah and Texas. Releases in Arizona and New Mexico are on hold until the results of the other tests are known, because in these areas saltcedar has become a common nesting site for the endangered southwestern willow flycatcher, primarily because the tree has supplanted native willow. Saltcedar now occupies more than half the vegetated land along many Southwest streams.
The quarter-inch long beetle is a good prospect for biocontrol of saltcedar because both larvae and adults feed exclusively on the plant, and the adults produce two or more generations of offspring per year. They not only eat the green vegetation, but in doing so create holes in the leaves through which water escapes, causing branches to wither and die.
A three-year test in the field with beetles confined to cages showed that the beetle can survive the winter and reproduce, and that it effectively defoliates saltcedar.
Dudley and saltcedar project leader Jack DeLoach of the USDA ARS in Temple, Texas, conducted an ecological assessment of the potential impact the beetles would have on wildlife and other plants. Based on the study, Dudley expects that the beetle will be most effective at killing seedlings, thus preventing the spread of saltcedar, and at stressing adult trees so that willow and cottonwood can compete more effectively. That way, the flycatcher and other wildlife or plants that have adapted to saltcedar can gradually return to their native hosts.
Revegetation may be necessary to restore native trees, but that can be undertaken by farmers and ranchers themselves, said entomologist Raymond I. Carruthers, research leader for the Exotic & Invasive Weeds Unit at the Albany ARS, which administers the consortium.
"We're trying to get people together and give them a solution they can take and apply to their own land," he said.
The saltcedar is an ideal plant for biological control because it has no close relatives in North America. As a result, insects that feed on saltcedar and are imported from other countries are unlikely to find native American plants or crops to their liking and become a pest in their own right.
Saltcedar is in the genus Tamarix, which comprises 54 species found only in the Old World, stretching from southern Europe through the Middle East to Central Asia. Some 10 species were introduced into the United States in the early 1800s as ornamentals, windbreaks or to stabilize soil. Since then two species - Tamarix parviflora in coastal and central California and Tamarix ramosissima in more arid areas - have invaded nearly every river floodplain and every lake shore in the West, forming dense thickets that narrow, deepen and often block stream channels to cause floods. It is estimated that saltcedar occupies more than 1.5 million acres of western land today.
Saltcedar also pushes out native plants, such as willow and cottonwood; sucks up twice the water that willow does; and draws salt from deep in the soil and deposits it on the surface, killing understory plants. It supports fewer insects than native vegetation, and thus fewer declining riparian-dependent migratory birds. Cows won't touch it, and it interferes with access to public and private rivers and lakes.
"In some areas the saltcedar gets so thick that wildlife can't even cross streams," Carruthers said. "It's like a briar patch."
For these reasons, supporters of the consortium include several water companies, such as Los Angeles Water & Power and the Yolo County (Calif.) Water Department, and cities like Woodland,
Calif., which has suffered frequent floods as a result of salt cedar infestation of Cache Creek. Herbicide spraying and bulldozing have been ineffective because the tree grows back.
Jan Lowery of the Cache Creek Conservancy near Woodland also is cooperating with the biological control project as one of the only ways to keep on top of the regrowth problem.
Other consortium members include UC Davis, Texas A&M, New Mexico State University, University of Wyoming, U.S. Bureau of Land Management, U.S. Fish & Wildlife Service and USDA's Animal & Plant Health Inspection Service.
"The strong point of the consortium is that we have gotten people from different perspectives to look at, research and document how well biocontrol works against the saltcedar," Carruthers said.
The USDA started researching biological control for saltcedar in 1987, and together with outside biologists has collected several promising insect pests of the tree from the Old World, where some 240 insects feed on the plant. The Chinese leaf beetle Diorhabda elongata has been studied in quarantine at the USDA's Temple, Texas, station for the past eight to nine years, led by DeLoach. For the past three years, UC Berkeley scientists, in cooperation with the Albany ARS, have tested the beetle's effectiveness. In 1999 the researchers set up cages in saltcedar areas to raise beetles, and these cages are now helping to supply the several thousand beetles that will be released eventually at each of 11 sites in six states.
Carruthers at the U.S.D.A. and consortium colleagues, including Dudley and UC Berkeley associate professor of integrative biology Carla D'Antonio, this year embarked on a five-year, $3 million project to assess the impact of biological controls against saltcedar and two other invasive pests, Arundo donax or giant reed, and the star thistle, a yellow-flowered weed that has taken over valuable ranch and wild land throughout California, Idaho, Oregon and Washington.
"The grant pays for field work and follow-up monitoring to find out what are the real risks and economic and ecological benefits of biological control," Dudley said. "This will be the most intensively
researched biological control program ever conducted in the U.S. or any other country to evaluate the success of the introduced insect in establishing and affecting the plant, and to document the recovery process of riparian ecosystems impacted by non-indigenous pests."
Carruthers predicts there will be other insect releases to control saltcedar. In fact, two small flower-eating weevils from France are under study now in quarantine at the Albany ARS, as is a small fly called a gall midge that lays eggs in twigs and deforms the plant.
"We will bring them in as we find we need them," Carruthers said. "Each carries its own benefits and risks, though, so we want to use as few biological agents as necessary to do the job."
The research is supported by the U.S. Department of Agriculture and various cooperating agencies, including U.S. Fish and Wildlife Service, the Bureau of Land Management and the Bureau of Reclamation. Additional resources and in-kind services have been provided by a number of private and non-governmental organizations.