Orius insidiosus (Say) as a predator of the soybean aphid, Aphis glycines Matsumura

The soybean aphid, Aphis glycines Matsumura, a pest of soybeans in Asia, invaded North America recently. The indigenous generalist predator Orius insidiosus (Say) is common in Midwestern US soybean fields throughout the soybean-growing season. From its phenology and abundance, we hypothesize that this predator could act to suppress soybean aphid population growth by attacking aphids during the critical period when aphids are first colonizing soybean fields. Therefore we conducted a series of laboratory assays of O. insidiosus to evaluate the conditions under which it may effectively suppress aphid population growth. We conducted a standard functional response experiment and found that O. insidiosus had a maximum attack rate of 19.25 (±0.06 SE) aphids in 24 h. We examined the ability of O. insidiosus to suppress aphid population growth over a four-day period in microcosms with different numbers of aphids, plant sizes, and plant numbers. We found that predators were able to effectively suppress aphid population growth, but that their efficacy depended upon the number of prey present and characteristics of the plant on which prey were found. Further, we showed that O. insidiosus was able to suppress aphid population growth below starting densities for an extended time period (12 days). These results suggest that under certain conditions, O. insidiosus can effectively suppress aphid population growth and that they may be key factors influencing aphid population dynamics in soybeans.