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Issue No. 24, Article 4/November 11, 2005

Captures of Soybean Aphids in Suction Traps for 2005

Having experienced yet another set of circumstances related to soybean aphids in Illinois in 2005, we begin wondering what will happen in 2006. As most of you know, captures of winged soybean aphids in the fall (as they fly from soybeans to buckthorn) provide some insight into the potential for soybean aphid problems the following year.

Our ability to predict soybean aphid densities from this trapping effort--initiated by Dr. David Voegtlin, Illinois Natural History Survey, in 2001--is far from foolproof. However, captures of soybean aphids over time should help us refine our predictions, especially as results from complimentary research efforts contribute new information. Many Midwest entomologists are so interested in results from the operation of the suction traps that we now have a regional network of traps--9 in Illinois, 6 in Indiana, 4 in Iowa, 3 in Michigan, 4 in Minnesota, and 5 in Wisconsin. You can view captures of winged soybean aphids throughout the season in all states at http://www.ncipmc.org/traps/.

Through the end of October 2005, the suction traps in Illinois had captured significantly fewer soybean aphids than was true a year earlier. Dave Voegtlin supplied the following numbers of soybean aphids captured in all traps in Illinois in September and October over the past five years:

  • 2001 (seven traps)--24
  • 2002 (eight traps)--732
  • 2003 (nine traps)--71
  • 2004 (nine traps)--1,700
  • 2005 (nine traps)--269

So what do these numbers mean? Voegtlin points out that soybean aphid problems were minimal in Illinois during the years after two-digit counts of aphids in the fall. In contrast, problems were significant (although occasionally regional) in Illinois during the years after three-digit counts of aphids in the fall.

What does a count of 269 aphids (captured in nine traps) in September and October 2005 mean for 2006? As we learned first-hand in 2005, the answer cannot be based solely on captures of aphids in suction traps the previous fall. Questions about other contributing factors abound: What is the level of predation of soybean aphids on buckthorn? Is it possible to find soybean aphid eggs on buckthorn? What weather conditions will prevail during the spring and summer of 2006? Will soybeans be planted early or late in 2006? What effect did insecticide applications in 2005 have on soybean aphids?

We still have much to learn about an insect that has become almost as important to soybean production as corn rootworms are to corn production. And as with corn rootworms, predictions will be only as reliable as the information garnered from regular scouting visits.

Entomologists in the Midwest will be meeting occasionally during the winter months to share information and data and to refine soybean aphid management recommendations. As we learn more from these meetings, we will share any information that will improve your ability to manage soybean aphids.--Kevin Steffey

Kevin Steffey

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