This past growing season, soybean aphids were unable to develop economic infestations in most fields in the North Central region, according to University of Illinois professor of entomology and crop sciences extension coordinator Mike Gray.
“Is the ‘every other year’ infestation prediction a bust?” he wondered.
Former Illinois Natural History Survey entomologist David Voegtlin, a well-known expert on soybean aphid population dynamics, noted that in 2012, this insect had its lowest impact since it came to prominence a little more than a decade ago.
“This past year, infestations began early and then disappeared in most areas,” he said.
He explained that the anemic soybean infestations of the past several years are due to both environmental and biotic factors.
“A fungus effectively eliminated many of the fall migrants once they reached their overwintering host, buckthorn, in both 2009 and 2010. Densities of soybean aphids as monitored by suction traps during the fall flights in 2011 and 2012 have been extremely low,” he said.
Voegtlin believes low trap numbers serve as a better predictor of future population trends than large trap captures. Thus, he expects that overwintering densities (eggs on buckthorn) will be low, with a very small spring flight of aphids to soybean fields in many areas of the Midwest next year.
In late October, Voegtlin will conduct surveys of buckthorn to determine what the egg count looks like. Gray said that he may have a difficult time finding colonies. In addition to biotic factors, the extreme heat of the past two summers has had a significant and negative impact on aphid survival. One other factor that may be contributing to the overall reduced abundance of soybean aphids is the widespread use of insecticidal seed treatments.
“It will be interesting to see what the next several years bring with regard to soybean aphid abundance,” said Gray. “At this point, the ‘every other year’ soybean aphid infestation cycle does not appear to be a reliable predictor for producers.”