For many areas of the North Central region this past growing season, soybean aphids were unable to develop economic infestations in most producers' fields. David Voegtlin, a well-known entomologist (retired from the Illinois Natural History Survey) and an expert on soybean aphid population dynamics, believes that in 2012 this insect had the lowest impact since it came to prominence a little more than a decade ago. This past year, Dave indicated, infestations began early, then "disappeared in most areas."
Why have soybean aphid infestations been so anemic the past several years? Dave attributes the answer to both environmental and biotic factors. In both 2009 and 2010, a fungus effectively eliminated many of the fall migrants once they reached their overwintering host (buckthorn). Densities of soybean aphids as monitored by suction traps during the fall flights of 2011 and 2012 have been exceedingly low. Dave believes low trap numbers are a better predictor of future population trends than large trap captures. This would suggest that overwintering densities (eggs on buckthorn) will be low and that next spring we will witness a very small spring flight of aphids to soybean fields in many areas of the Midwest.
In late October, Dave will conduct surveys of buckthorn to determine what the egg count looks like. He may have a difficult time finding colonies this fall. In addition to biotic factors, the extreme heat the past two summers has significantly and negatively impacted 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. At this point, the every-other-year soybean aphid infestation cycle does not appear to be a reliable predictor for producers. I offer my thanks to David Voegtlin for his continuing leadership in coordinating the collection of data from the network of suction traps across the North Central region.