The age of soybean aphids reached its fifth year in 2004.  Since their arrival, we have learned much about this insect pest, but there is obviously still a lot that we don’t know.  Locally, cool weather and a bunch of late planted fields would have pointed to big problems with soybean aphids in 2004.  As it turned out, they were all but a no-show. 

        Since aphids jumped on the scene in 2000, their relative abundance has been cyclic.  That is, high densities one year and low densities the next.  It remains to be seen whether this cycle will continue.  David Voegtlin, an entomologist at the Illinois Natural History Survey, has led an effort to trap soybean aphids during their fall flight to overwintering hosts (primarily buckthorn) in September.  Over the course of the past four years, an interesting pattern has developed whereby heavy fall flights have been followed by a year with large densities of aphids in soybeans, and vice versa.  Hence, it seems reasonable to assume that soybean aphid problems in any given year might be predicted by the trap counts from fall flights. 

Why the cyclic pattern?

        It remains somewhat curious as to why soybean aphids seem to thrive every other year.  One possible explanation relates to the relative abundance of multicolored Asian lady beetles.  It’s been noted that when there are large fall populations of beetles, which are a natural predator of the soybean aphid, there are low populations of aphids. 

What about 2005?

        Fall soybean aphid trap counts this year have been high and the fall migration to buckthorn has been about two weeks earlier than the flight of 2002.  Further, more male aphids are being trapped compared to normal.  This information offers potential for another big soybean aphid year in 2005.  However, just as many baseball players with great potential have only seen Cooperstown from a tour bus, it’s still a good practice to be vigilant in scouting as the 2005 growing season unfolds.  Environmental conditions this winter and next growing season may put the whammy on a significant aphid outbreak.  The Illinois fall aphid trap counts are available on the Internet for viewing at:  

www.ipm.uiuc.edu/fieldcrops/insects/soybean_aphids/suction_trap_network/