July 19, 2006 | By: Laura Skillman

Soybean aphids found recently in Lexington may mean the insect thought not to overwinter in Kentucky has done so – at least in this isolated incidence. However, this find does not mean any change in how farmers’ manage the pest, said Doug Johnson, entomology professor with the University of Kentucky College of Agriculture.

What it does mean is the need for more research to find out where the potentially damaging insect might be overwintering and to elicit the help of a UK botanist to identify the host. Once found, the host will be monitored to see if the aphid returns to it in the fall and if the aphid is sexually reproducing in the state.

The non-native species was first discovered in the north central United States during the 2000 and 2001 growing seasons. Until this recent find, it was believed it could not overwinter in the state because its primary host, buckthorn (Rhamnus cathartica), is rare in Kentucky.

“Basically, our operating theory and the lack of a huge presence in Kentucky has been predicated on two things,” Johnson said. “One is we felt like most, if not all, of the aphids we get migrate in from the northern United States. Because of its complicated life cycle it has to have a primary host to overwinter on and that primary host is a tree that we don’t have very much of so we don’t see much of the aphid until later in the year. The other part is research work done in Wisconsin indicates the aphids do not do well in high temperatures. Their comfort zone is high 70s to low 80s, so we postulated that maybe one of the reasons we don’t get large populations is that it gets so hot during the growing season here it slows reproduction and movement.”

Johnson said he was not surprised the first soybean aphids found this year were in Lexington because UK soybean breeder Todd Pfeiffer has always been the first person in the state to find them. That is because he’s generally the first person looking for them. 

While Johnson said he’d never been overly concerned about early finds in Lexington in the past, this year is different.

“There have been no migrant aphids caught in the national suction trap network, and there’s been fairly low aphid numbers across the northern United States and even southeast Canada,” he said. “So, this population being here is very strong evidence that it did not occur from an influx of migrants. It occurred from aphids infesting the plants from an overwintering host, which means we have the host at least somewhere in Kentucky.

In the short term, finding an early population and confirming that the insect is overwintering in the state will not impact the currently recommended crop management strategy of “watch, wait and look for large populations then treat if necessary,” Johnson said. But as researchers work to piece together more about the insect and its capabilities of overwintering in Kentucky, it could have long-term consequences.

“If we start finding pockets where it is overwintering or that it has adapted to a new overwintering source, the management strategy changes,” he said.

Up-to-date information on soybean aphid populations in Kentucky can be found on the Internet at http://www.sbrusa.net or by calling 888-321-6771.



Doug Johnson, 207-654-7541, ext. 214