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Keeping an Eye Out for the Corn Farmer's Best Friend

By Don Comis
January 17, 2003

Ground beetles may not be welcome to city folk who mistake them for small cockroaches, but they are more than welcome in cornfields because they can be voracious predators of the corn farmer's worst pest, the corn rootworm.

Corn rootworms eating away at corn roots cause farmers to spray more insecticide than do any other pest in the United States.

Ground beetles are so important that Agricultural Research Service scientists are monitoring their populations to ensure that new pesticides--including natural insecticides produced by new varieties of corn plants--don't harm them. As part of this effort, ARS scientists have designed a new, revolving trap that operates like a clock.

ARS entomologist Mike Ellsbury created the new trap by modifying a mosquito trap that hangs from a tree. The clockwork trap rotates so it catches the beetles in one of eight bottles every three hours, allowing Ellsbury to learn what species are active when. Ellsbury attached the rotating trap mechanism to a plastic disc, then covered the disc with soil and plant litter, completely disguising it, leaving only a single pitfall opening exposed.

There are more than 20,000 species of ground beetles in the family Carabidae. Knowing when different species are active offers diet clues that can be helpful in protecting ground beetles and in learning how their numbers can be maintained or even increased.

Ellsbury has three of the new traps and plans to build more. He also has 105 conventional single pitfall traps and has placed the traps in experimental plots of corn. By keeping track of the location, numbers and species of ground beetles, Ellsbury and colleagues will learn whether the new corn varieties have any harmful effects on the beetles.

With corn rootworm evolving ways around the crop rotations traditionally used to control it, ground beetles are increasingly becoming a corn farmer's best friend.

ARS is the U.S. Department of Agriculture's chief scientific research agency.