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[MARCH 29, 2004]  URBANA -- Some early-season clues suggest that the soybean aphids may not be as troublesome in the upcoming growing season as they were in 2003, according to entomologist Kevin Steffey from University of Illinois Extension.

In 2001, David Voegtlin from the Illinois Natural History Survey established a network of suction traps so that scientists could monitor the flights of soybean aphids throughout any given season.

"Captures of soybean aphids in these traps have been pretty revealing, and some trends may be starting to develop," Steffey said. "For example, captures of flying soybean aphids in the fall of 2002 were noticeable, while there were no captures of flying soybean aphids in the fall of 2001."

Steffey notes that, because an outbreak of soybean aphids occurred in 2003 and there were few soybean aphids 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," he said. "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."

Steffey points out that very few of these lady beetles were found during the fall of 2002, while there were hordes of these lady beetles in 2003.

"It seems obvious that when soybean aphids are scarce, then multicolored Asian lady beetles also are scarce," Steffey said. "As a consequence, soybean aphids were able to establish populations and begin population growth in the relative absence of lady beetles early in 2003.


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When soybean aphids were plentiful, such as in 2003, then multicolored Asian lady beetles also become plentiful after a lag time during the summer.

"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," he said. "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, while 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," Steffey said. "At the first appearance of soybean aphids, we will let growers know when and where."

Steffey advises growers, however, not to overreact at the first occurrence of soybean aphids in soybean fields in their area.

"Their populations will bear watching, but spraying an insecticide too early at the first appearance of soybean aphids may cause more problems than it will solve," he said.

[University of Illinois news release]


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