Issue No. 1, Article 7/March 18, 2004
Soybean Aphids in 2004?
The outbreak of soybean aphids in 2003 left a bad taste in the mouths of soybean producers, even through the winter. Many people are wondering whether this pest will return in force in 2004 or will be less than obvious, as it was in 2002. Although we have learned quite a bit about soybean aphids since 2000, when the insect first was discovered in North America, we still can't predict its occurrence. However, some clues suggest that soybean aphids may not be as troublesome in 2004 as they were in 2003.
In 2001, Dr. David Voegtlin, aphid research specialist in the Center for Economic Entomology in the Illinois Natural History Survey, established a network of suction traps to enable us to monitor the flights of soybean aphids throughout any given season. The captures of soybean aphids in these traps have been pretty revealing, and some trends may be starting to develop. For example, captures of flying soybean aphids in the fall of 2002 were noticeable, whereas there were no captures of flying soybean aphids in the fall of 2001. Because an outbreak of soybean aphids occurred in 2003 and soybean aphids were few and far between in 2002, the capture of aphids during the fall may provide some insight into the potential for infestations to develop the following season. It is interesting to note that very few aphids were captured in the suction traps during the fall of 2003. You can examine the records of captures of soybean aphids at http://www.ipm.uiuc.edu/fieldcrops/insects/soybean_aphids/suction_trap_network/index.html.
The presence or relative absence of the multicolored Asian lady beetle, the primary predator of soybean aphids, also may play a role in regulating populations of soybean aphids. Very few of these lady beetles were noted during the fall of 2002; however, we were subjected to hordes of them in 2003. It seems obvious that when soybean aphids are scarce (as they were in 2002), multicolored Asian lady beetles also are scarce (less food to sustain their populations). As a consequence, soybean aphids were able to establish populations and begin population growth in the relative absence of lady beetles early in 2003. On the other hand, when soybean aphids are plentiful (as they were in 2003), multicolored Asian lady beetles also become plentiful, after a lag time during the summer. This is a classic predator-prey relationship.
The relatively low numbers of soybean aphids captured in suction traps in the fall of 2003 and the presence of very large numbers of multicolored Asian lady beetles suggest that soybean aphids may not get off to a fast start in 2004. However, the weather conditions during the summer of 2004 may encourage the growth of soybean aphid populations in some areas. Soybean aphid populations thrive when conditions are relatively cool (as they were during the summer of 2003), and their population growth slows when temperatures are high.
We will be monitoring aphid captures in the suction traps and aphid densities in soybean fields throughout the season. At the first appearance of soybean aphids, we will let you know when and where. However, you should not overreact to the first occurrence of soybean aphids in soybean fields in your area. Their populations will bear watching, but spraying an insecticide too early may cause more problems than it will solve.
If you are interested in perspectives on soybean aphids from four different states (Illinois, Iowa, Minnesota, and Wisconsin), you can view slide sets posted at http://www.ipm.uiuc.edu/fieldcrops/insects/soybean_aphids/workshop/index.html. These slides were used during a February 5 workshop delivered by data conference by Drs. David Voegtlin, Marlin Rice (Iowa State University), Ken Ostlie (University of Minnesota), Eileen Cullen (University of Wisconsin), and me. Approximately 800 people at 60 different sites in the four states participated in the program. In future issues of the Bulletin, we will borrow liberally from the information in these slide sets and provide updated information as research projects generate results.--Kevin Steffey