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Wee Wasps Vanquish Big Bad Beetles

By Linda McGraw
October 27, 1999

Good things really do come in small packages. Just ask Agricultural Research Service entomologists in Manhattan, Kan., who found that tiny, normally harmless wasps about a quarter-inch long can control insect pests in stored grains.

Biological control is an important part of integrated pest management for stored commodities such as wheat, corn, or grain sorghum, according to Paul W. Flinn and David W. Hagstrum of ARS’ Grain Marketing and Production Research Center. Damage caused by larvae of the lesser grain borer, rice weevil and maize weevil costs the U.S. wheat industry millions of dollars annually.

The tiny wasps, Theocolax elegans, don’t feed on grain but on lesser grain borer larvae that typically attack commodities stored in bins and elevators.

For their study, the researchers used six 1,000-bushel bins filled with wheat. They released the parasitic wasps into three of the bins. Next, they released lesser grain borers into all six bins. After 131 days of storage, the beetles were reduced by 91 percent in the treated bins compared to the bins without wasps.

The Manhattan researchers then milled the wheat flour and sent it to the Federal Grain Inspection Service in Kansas City, Mo. FGIS analyzed it for insect fragments. Flour from the wheat exposed to wasps had 89 percent fewer insect fragments than flour from the control bins. That’s because the harmless adult wasps stay outside the grain kernels, so they are easily removed when grain is cleaned in flour mills.

Scientific contact: Paul W. Flinn, ARS Grain Marketing and Production Research Center, 1515 College Avenue, Manhattan, KS 66502, phone (785) 776-2707, fax (785) 537-5594,