Monday, December 11, 2006 - 10:47 AM

Effects of reduced risk-insecticides on the soybean (Glycine max) natural enemy community

Wayne J. Ohnesorg, and Matthew E. O'Neal, Iowa State University, Entomology, 113 Insectary, Iowa State University, Ames, IA

Natural enemies are an important part of soybean aphid (Aphis glycines Matsumura (Hemiptera: Aphididae) management. Broad spectrum insecticides, like lambda-cyhalothrin, are frequently used to control soybean aphids but reduce natural enemy abundance. Insecticides considered reduced-risk when, by mode of action or method of contact, have limited exposure to non-target species. Our objective was to determine if reduced-risk insecticides have a limited impact on the natural enemy community in soybeans. During the 2005 and 2006 growing season we applied lambda-cyhalothrin (Warrior®) and several potential reduced-risk insecticide to small plots of soybeans with naturally occurring soybean aphid populations. Reduced-risk insecticides included; nicotinoid seed treatments imidacloprid (Gaucho®) and thiamethoxam (Cruiser®), a foliar applied imidacloprid (Trimax®) and foliar applied pymetrozine (Fulfill®). Products were chosen based on mode of contact (systemic; imidacloprid and thiamethoxam) and selectivity for aphids (pymetrozine). We monitored soybean aphids and associated natural enemies before application of the foliar applied insecticides and at a 3-week period post-application. Aphids and natural enemies were sampled by visual inspection of the plant and sweep-nets. Regardless of mode of action, foliar applied insecticides provided greater control of soybean aphids than seed treatment, which were not significantly different from our untreated plots. The foliar insecticide lambda-cyhalothrin had the greatest reduction in total natural enemies. Seed treatments, the foliar applied imidacloprid and pymetrozine had no observable effect on the natural enemy community, including Orius insidiosus (Hemiptera: Anthocoridae) a soybean aphid predator known to feed on soybeans during times of low prey availability.

Species 1: Hemiptera Aphididae Aphis glycines (soybean aphid)

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