No. 12 Article 2/June 10, 2005

Follow-Up on Reports of Soybean Aphids

Entomologists in several midwestern states have reported finding soybean aphids in soybean fields. In addition to the discoveries in Illinois and Indiana, soybean aphids have been confirmed in soybean fields in Iowa, Michigan, Minnesota, and Wisconsin. In all instances, the numbers of aphids found in a given field have been extremely low--one here, two there, four over there. However, as we all know, the reproductive capacity of soybean aphids is remarkable, so their numbers can increase dramatically in a relatively brief period of time. Within days, small colonies of aphids on individual soybean plants should be evident in fields in which alates originally alighted. It will be interesting to learn how temperatures above 85°F affect the development of soybean aphid populations in Illinois and elsewhere.

Since our report in the Bulletin last week, we have received a handful of additional reports of soybean aphids in soybeans in Illinois. Russ Higgins, Extension IPM educator in Matteson, found eight, five, and three aphids on three different V2-stage plants in a field in Grundy County during the June 4-5 weekend. The aphids all were located in the most recently unfurled trifoliolates. Jeff Wessel, farm manager at Joliet Junior College, found "a dozen or so" aphids on three different V1- to V2-stage soybean plants on June 2. Jim Donnelly, staff agronomist with Ag View FS, collected alates from a buckthorn plant and caged them on a soybean plant. Jim observed that the alates settled on the soybean plants and began to produce nymphs. In addition, Jim found a soybean aphid in a soybean field in Bureau County on June 6.

Despite all of these confirmations of soybean aphids in soybean fields, we need to keep everything in perspective. On June 7, I and two undergraduate employees working with us this summer embarked on a quick trip for surveillance of soybean aphids in northwestern Illinois. We did not sample a large number of fields (only two to three fields per county), and we generally examined only 30 plants per field. Nonetheless, we found no soybean aphids in any of the fields we surveyed in Carroll, JoDaviess, Ogle, Rock Island, Stephenson, and Whiteside counties. This does not mean that soybean aphids are not present in northwestern Illinois. However, our inability to find soybean aphids easily indicates that the aphids are just beginning to colonize. So finding soybean aphids right now may require some diligent scouting.

That's the good news--the numbers of soybean aphids in soybean fields right now are small. The potential bad news is that the numbers of soybean aphids could increase quickly. So keep up the scrutiny. We will conduct regular surveys this summer to keep abreast of the population dynamics of soybean aphids in Illinois. Please help flesh out our reports by reporting your own findings. The more eyes we have looking for these pests, the more likely we will know in advance whether densities of soybean aphids will become threatening.--Kevin Steffey

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