Natural Enemies of Russian Wheat Aphid Established in 6 States

Ten years after scientists released millions of exotic wasp parasites in small grain fields in eastern Colorado to control the Russian wheat aphid, they've found that four wasp species have become established in six states.

Since invading the United States in 1986, the green, 1/16-inch-long aphids have caused more than $1 billion in insecticide costs and related losses. Conventional breeding has produced aphid-resistant wheat varieties. But these varieties aren't yet available to producers.

In 1988, to screen natural controls for the Russian wheat aphid, Agricultural Research Service scientists worked with a consortium of federal and state scientists to release 11 species of wasps. These imported, exotic enemies of the pest were released in the wheat and barley growing areas of the western United States. The 11.8 million parasitic wasps released represented more than 80 geographic strains collected from 25 different Eurasian countries where the aphid originated.

From 1991 through 1993, ARS scientist John D. Burd at the Plant Sciences and Water Conservation Research Laboratory in Stillwater, Okla., working with USDA's Animal and Plant Health Inspection Service, the Colorado State Agricultural Experiment Station and the Colorado Department of Agricultureconducted an intensive biological control release program. Its purpose: to establish natural enemies of the aphid in small grains in eastern Colorado.

Burd's group released seven wasp species into Russian wheat aphid infested wheat fields.

Now, seven years later, Burd reports that four of the seven wasp species have become established throughout a six-state area--Colorado, Kansas, Montana, Nebraska, Oklahoma and Wyoming. Three species were found parasitizing greenbugs, an aphid relative, on sorghum. Two species successfully parasitized the Russian wheat aphid on wild grasses that aphids used as host plants over summer.

It's important to establish natural enemies as part of integrated pest management systems because they do not cost anything, are highly compatible with plant resistance, and can contribute considerably to the overall reduction in the reliance on insecticides to control aphid cereal pests.

ARS is the chief research arm of the U.S. Department of Agriculture.

Scientific contact: John D. Burd, ARS Plant Sciences and Water Conservation Research Laboratory, Stillwater, Okla., phone (405) 624-4141, ext. 223, fax (405) 624-4142, [email protected].