November 1, 2001 | By: Laura Skillman

The soybean aphid was found in several North Central states and Kentucky, during the 2000 and 2001 growing seasons.

The pest is new to North America. Extension and research entomologists and plant pathologists at the University of Kentucky College of Agriculture are watching the progress of this aphid and conducting research on its possible effects in the state.

"While in Kentucky, there is not currently a problem with the soybean aphid, it is present in the state and we need to continue to watch for outbreaks," said Doug Johnson, UK Extension entomologist stationed at the Research and Education Center in Princeton.

The three-year research project is being funded by a grant from the Southern Region Integrated Pest Management Competitive Grants program.

The soybean aphid is a native of China but has spread along the western Pacific and is known from Korea to the Philippines. It also has recently been found in Australia. The source of the aphids that began the infestation in North America is not known but they are believed to have been in the states for three to four years.

In addition to their own research, UK specialists are cooperating with a working group in the North Central states which is monitoring the spread of the pest and developing management information and guidelines.

Kentucky is in the U.S. Department of Agriculture's Southern region not the North Central region but because the aphids are being found in the state, UK is a part of the aphid working group. Johnson is the Kentucky liaison.

The insects have been found virtually statewide, Johnson said. But in low numbers.

"We are talking very small numbers, not enough to cause economic damage," he said.

At this point, entomologists believe the aphids cannot overwinter in Kentucky because their primary host, buckthorn, Rhamnus cathartica is rare in Kentucky. These insects can reproduce both sexually and asexually. Sexual reproduction can only occur on certain plant species and that is the one known to be in the United States.

"So that means we get ones that migrate in from the north," Johnson said. "That's extremely important because if they could overwinter here we'd have them from day one. It's important to understand that that's the current standard of knowledge, but we've only been working on this for a year. We could find out that there are more Rhamnus cathartica in the state than we think or that there are other hosts on which they can overwinter."

UK's aphid research is two pronged. The soybean aphid feeds on the plant but is also capable of transmitting a number of viruses present in the United States that naturally infect soybeans, including alfalfa mosaic, soybean mosaic, bean yellow mosaic, peanut mottle, peanut stunt and peanut stripe. Theses viruses may all be in Kentucky as well, although peanut stunt and stripe are probably only in very low levels, according to Don Hershman, UK Extension plant pathologist.

Plant pathologists are studying whether there are increased incidents of soybean viruses and what will happen to these viruses. These viruses have been here but have not had anything to move them around the plants. This insect could be the bridge to move it from plant to plant, Johnson said. That could become very important.

"It's all associated with how long they are subjected to it," he said.

Young plants, may be dead at end of the season while ones not subjected to viruses and aphids until late in the growing season, may not be impacted.

Entomologists are looking at what is currently used in the soybean production system and how it will affect the growth rate of aphids on the plants. Those include planting date and maturity groups.>P> Also, researchers are determining what biological control agents are in Kentucky's soybean fields that would control the aphid populations. While the 2001 test plots have not yet been harvested, they have determined that as fast as the aphids where placed into fields by researchers something comes along and eats them - primarily lady beetles, he said.

"We do know that there are a number of natural enemies that will feed on the insect and feed very heavily on the insect," Johnson said. "There are some questions still about what will happen when you have a few aphids drifting in at a time.

"Right now, we don't see any eminent problems," he said. "It is relatively easy to kill them, but you can build a population with insecticides. If you spray when you don't need to, the spray will kill most of the aphids but you will also kill all its natural enemies in the field and then the aphid population will take off."

Kentucky does not have an insect in field crops that has this rebounding potential, Johnson said. This one has that potential. The soybean aphids in Kentucky are all female, in the asexual form. They already have live young. When a new baby female hits the leaf, it already has baby females, so they can grow populations very rapidly.

Annually, the insect is going to be a northern pest. For Kentucky, that question is yet to be answered. While they are believed to have to migrate into the state, if they find an overwintering host, there will be plenty of them.

"It is something people need to educate themselves on and look for but not be panicky about," Johnson said. "Regardless of the way the system works, it's going to take two to four years for this problem to build up where we have to worry about it and it may never or it may be one of those that we have to deal with every three or four years."


Doug Johnson, (270) 365-7541