Populations of western corn rootworm beetles in Ohio soybean fields were lower in 2001 than in 2000, according to a recent Ohio State University Extension survey.

Bruce Eisley, an Ohio State Extension entomologist, said western corn rootworm populations trapped in soybean fields have been decreasing every year since the surveys began in 1998.

With these beetles, yield loss may occur when trap catches are at two beetles per trap per day or higher. Extension personnel monitored traps in 76 fields in 19 counties in central and western Ohio from mid-July to late August. Average beetle counts in 75 percent of the fields were less than 0.20 beetles per trap per day. This compares with 70 percent of the fields with beetle counts less than 0.20 beetles per trap per day in last year's survey. The largest beetle count in the survey in 2001 was 0.72 beetles per trap per day.

"Based on these counts, first year corn rootworm does not appear to be a problem in Ohio at this time," said Eisley.

Western corn rootworm beetles are also known as first-year corn rootworm because they have, in recent years, begun laying eggs in soybean fields which hatch into larvae and feed on corn that has been planted into those fields the following year. The beetles damage the root system and may cause yield loss.

Eisley said that he has not received any reports about first year corn being damaged by corn rootworm in Ohio. "We still need to sample soybean fields in the future to make sure that first year corn rootworm does not become a problem for Ohio growers."

Monitoring for first-year corn rootworm is accomplished by placing yellow sticky traps in soybeans from mid-July to late August. The traps are changed periodically and the beetles are counted per trap. The average number of beetles captured per trap per day is calculated and used to determine population levels.