Soybean aphids are now being observed on buckthorn, their overwintering host in Ohio. Various natural enemies are present, including multicolored Asian lady beetles and syrphid fly maggots. A few eggs have been laid on the buckthorn near the buds for next year's growth. The egg is the life stage in which the soybean aphid overwinters.
In most years that are considered “soybean aphid” years such as 2011, we would not expect to see large numbers of soybean aphids on the buckthorn nor eggs being laid; aphids on buckthorn in the fall usually happens during “non-aphid” years which provides the aphid populations for the following year. However, in 2009, our last “aphid” year, we also experienced aphids colonizing buckthorn which was a surprise and made us wonder if the 2-year cycle had been broken. However, aphid populations were high that fall when an apparent pathogen came in, causing severe aphid mortality and resulting in 2010 being a non-aphid year keeping the 2-year cycle. You can read a series of articles on this occurrence at http://corn.osu.edu/newsletters/2009/article?issueid=324&articleid=1928; http://corn.osu.edu/newsletters/2009/article?issueid=329&articleid=1948; and http://corn.osu.edu/newsletters/2010/2010-10/soybean-aphid-populations-not-being-found-on-buckthorn.
Whether aphids now on buckthorn lay sufficient numbers of eggs that successfully overwinter will not be known until next spring and summer. Will we see a repeat of 2009-2010, and maintain our two-year cycle and have a low aphid year next year, or will we have aphids next summer in 2012? That will need continued observations through next spring and summer to answer these questions.