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Soybean Aphids--A Caution About Jumping to Conclusions

May 18, 2001
In last week's issue of the Bulletin (no. 7, May 11, 2001), I wrote a brief article about David Onstad (associate professor in the Department of Natural Resources and Environmental Sciences) finding the first soybean aphids of the season in Illinois. He found a couple of aphids (purportedly soybean aphids) on a buckthorn plant in Kane County during the week of May 7. However, David Voegtlin, our resident aphid expert at the Illinois Natural History Survey, has not verified the species. Therefore, my report about "the first soybean aphids of the season" was premature.

The reason the lack of verification of species is important is that David V. also has found another species, Aphis nasturtii, on Rhamnus in northern Illinois. This latter species, occasionally referred to as the buckthorn aphid, has been in North America for decades. Like the soybean aphid, A. nasturtii thrives on buckthorn during part of its life; unlike the soybean aphid, A. nasturtii does not feed on soybean or any other legumes.

This information once again underlines the importance of accurate identification of a pest (or nonpest) insect. During their early generations on Rhamnus, A. glycines (the soybean aphid) and A. nasturtii (the so-called buckthorn aphid) are very similar in appearance. Usually only an expert such as David Voegtlin can tell the species apart. So the message is this: if you find aphids on buckthorn this spring (I doubt that many people are looking, but one never knows), don't assume they are soybean aphids. The same principle applies when (if) we begin to find aphids in soybean fields. As the season progresses and David V. looks at more and more samples, we will have a handle on the species being found. Until then, we still are not sure that soybean aphids have "carried over" from last year.--Kevin Steffey

Author: Kevin Steffey

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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