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Project 15

Project title: Seasonal Occurrence of Parasitoids, Predatory Flies, and Pathogens Attacking Soybean Aphid and Impact of Soybean Aphid Chemical Control on Aphid Enemies
Investigators: Takuji Noma and Michael Brewer, Michigan State University, Integrated Pest Management Program, Department of Entomology, B18 Food Safety and Toxicology Building, East Lansing, MI
Contact: Michael Brewer (brewerm@msu.edu)

Project description:
We conducted field research in lower Michigan to assess seasonal occurrence of aphid parasitoids, predatory flies, and pathogens that prey upon soybean aphid (objective one). The effect of field-applied insecticides for soybean aphid control was also considered (objective two).

For objective 1, we found diverse communities of aphid specialist natural enemies attacking soybean aphid at two soybean sites in lower Michigan. They included 6 species of parasitic wasps, 9 species of predatory flies, and 1 species of pathogen. In addition to lady beetles and other predators previously documented, these aphid specialist enemies are naturally present in Michigan soybean fields. Species diversity and relative abundance of aphid enemies varied seasonally. In general, predatory flies tended to be more common early in the growing season while parasitic wasps tended to be more common late in the growing season. For fungal pathogens, one species was detected early August 2005, in which 90 % of winged aphids were infected. The epidemic was followed by the crash of soybean aphid population.

For objective 2, impact of an insecticide application on aphid-specialist enemies was tested in July, 2005 using replicated 1-acre soybean plots. Four plots were treated with insecticide (Warrior) and other four plots were untreated when soybean plants were at R3 stage. Natural enemies were sampled one week after the insecticide application. Predatory flies were the most abundant natural enemies and parasitoids were relatively rare. The insecticide application significantly reduced predatory fly populations by 91% compared with control populations, and 83% fewer predatory flies were recovered from the potted plants placed in sprayed plots than in untreated plots. The results confirm adverse impact of insecticide on aphid-specialist enemies present in soybean fields.