Six-Legged Italian Imports to Double-Team a Spiny Weed

TEMPLE, Texas, March 19--One thousand tiny flea beetles from Italy could be released in the United States for the first time this month, leading off the latest round of Agriculture Department scientists’ battle against musk thistle, a spiny pest in 32 states.

“We hope this flea beetle will complement three other insects we’ve imported, tested and released to attack musk thistle,” said entomologist Paul Boldt with USDA’s Agricultural Research Service here. The weed has taken over millions of acres of range, pasture, cropland, parks, roadsides and other areas in 32 states, he added.

About the end of March, Boldt plans to release Psylliodes chalcomera flea beetles at a test site near Comfort, Texas, about 40 miles northwest of San Antonio. They would join the Cheilosia corydon syrphid fly, another Italian insect first freed there in 1994. “We may learn this spring whether Cheilosia has made itself a permanent new home in this country,” said Boldt, with ARS’ Grassland, Soil and Water Laboratory.

Psylliodes flea beetles are also scheduled to be released this year at sites near DeSoto, Kan., and near Hagerstown, Md., Boldt said.

In tests in Italy, ARS entomologist Gaetano Campobasso and colleagues determined that the Psylliodes and Cheilosia insects will not harm U.S. native or crop plants including artichoke and chicory, two of musk thistle’s relatives.

ARS earlier obtained a permit to import both insects and to release Cheilosia from USDA’s Animal and Plant Health Inspection Service. Boldt will release Psylliodes flea beetles pending a final approval from APHIS. APHIS has made available an environmental assessment stating that releasing the beetles would have no significant adverse impact on the environment.

Campobasso collected Psylliodes and Cheilosia insects in southern Italy in early March and shipped the insects to Boldt. Campobasso works at the Rome substation of ARS’ European Biological Control Laboratory. The lab, based in Montpellier, France, is USDA’s primary European source of insects and microorganisms with potential as natural alternatives to chemical pesticides.

An article about the two scientists’ musk-thistle biocontrol research appears in the March issue of the agency’s’ Agricultural Research magazine (in press). Musk thistle, or Carduus nutans, originated in Europe and entered the United States 150 years ago. It grows about 6 feet tall, chokes out forage plants on range and pasture and displaces other desirable plants. Spines on the branches, leaves and flower heads ward off most animals, and cattle won’t graze near the weed.

Boldt said the spines also pose a pin-pricking hazard for unwary hikers who brush past the weed. “It’s tough to stop,” he said in the magazine article. “On rangeland, the benefit from herbicides isn’t worth the expense. And they can’t be used near areas such as beaches and parks.”

Boldt and Campobasso said biological control is the best long-term strategy. They’ve investigated a variety of thistle-loving insects since the 1970's. Two weevils that they and colleagues imported earlier are helping control the weed in several states. “We need a diverse team of insects to attack different parts of the plant at different times of year and in different climates,” Boldt said.

Larvae of the Cheilosia syrphid fly feed in the crown or rosette of young musk thistle plants, and on large flower-bearing stems. Immature Psylliodes flea beetles feed on the rosette and on leaf and flower buds. Adult flea beetles feed on the leaves.

ARS scientists are working closely with entomologist James Nechols of Kansas State University, Manhattan, to coordinate U.S. distribution of Psylliodes for the releases in Kansas and Maryland in 1997 and in about 20 other states in 1998.

Scientific contact: Paul Boldt, entomologist, Grassland, Soil and Water Laboratory, Agricultural Research Service, USDA, Temple TX 76502, phone (817) 770-6530, e-mail boldt@brcsun0.tamu.edu; and Gaetano Campobasso, entomologist, Rome, Italy, substation of the European Biological Control Laboratory, USDA-ARS, Montpellier, France, phone 011-39-620-609-346, e-mail ebcl.RomeSubstation@agora.stm.it. At APHIS, contact H. Nolan Lemon, Jr., Riverdale, Md., phone (301) 734-3266, nlemon@aphis.usda.gov.