More soybean, or "Chinese," aphids have been found in farm fields in 13 additional counties this fall, mostly south of the Missouri River and westward to Kansas City, says Wayne Bailey, University of Missouri (MU) extension entomologist.

However, infestations are later and smaller than expected, following the first discovery of the pest in most northeast Missouri counties in 2000.

"You have to look for them to find them," says Ben Puttler, MU extension entomologist. "We've dodged the bullet this year."

The counties with new infestations stretch from Osage County to Jackson County. Two new counties, Mercer and Livingston, were added in north-central Missouri. Heavy infestations were found as far west as Trenton, MO, in Grundy County in 2000.

New counties south of the river are: Osage, Cole, Moniteau, Cooper, Saline, Lafayette, Jackson, Pettis and Morgan. North of the river the pest was found in Howard and Chariton counties.

Puttler conducted searches in soybean fields in Cass, Henry, and Johnson counties last Friday, but did not find additional infestations. Most of the counties of Northwest Missouri remain un-infested. Bailey scouted fields in counties along the Kansas line as far south as Joplin, MO, without finding the pest.

"The heat and humidity in Missouri may affect the aphids more than it does in northern states," Bailey says.

"The new infestations probably came when the wind was blowing in that direction when they were moving," he adds.

The pest, a native of China and Japan, has a complex life cycle with the possibility of many generations in one year. However, the aphids require an alternative host, buckthorn, an ornamental shrub. Buckthorn, an introduced species, is found, but not extensively, in Missouri.

In heavily infested fields the aphids cause reduced plant growth and reduced seedpod set.

It was noted last year that the aphids have several natural enemies, including the Asian lady beetle and fungal pathogens.

"With the late start and light infestations, we don't expect to see much crop damage," Puttler says. "If there was damage our phones would be ringing."