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Title: Alfalfa living mulch advances biological control of soybean aphid

Author
item SCHMIDT, N - IA STATE UNIVERSITY
item O'NEAL, M - IA STATE UNIVERSITY
item Singer, Jeremy

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2006
Publication Date: 4/6/2007
Citation: Schmidt, N.S., O'Neal, M.E., Singer, J.W. 2007. Alfalfa living mulch advances biological control of soybean aphid. Environmental Entomology. 36(2):146-424.

Interpretive Summary: Introduction of the soybean aphid to North America has resulted in an insect pest of economic importance for soybean. Despite evidence for biological control in North America, soybean aphid outbreaks continue to occur. Our objectives were to determine if natural enemies delay aphid establishment and limit subsequent population growth and if this biological control can be improved by altering the within-field habitat. Soybean grown with an alfalfa living mulch had 45% more natural enemies, soybean aphid establishment was delayed, and peak populations were less than on soybean grown without a living mulch. Natural enemy abundance in soybean grown without the living mulch was sufficient to delay aphid population growth until more than 30% of the plants were infested with soybean aphid. We observed an impact of alfalfa on the quality of soybean as a host for soybean aphid, with reduced reproduction on soybean grown with a living mulch. Our results indicate conserving the natural enemy community before the arrival of soybean aphid can delay and suppress soybean aphid outbreaks. Soybean producers should consider the potential impact in-field cover crops may contribute in biological control of soybean aphid.

Technical Abstract: Introduction of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae) to North America has resulted in an insect pest of economic importance for soybean [Glycine max (L.) Merr.]. Despite evidence for biological control in North America, soybean aphid outbreaks continue to occur. Our objectives were to determine if natural enemies delay aphid establishment and limit subsequent population growth and if this biological control can be improved by altering the within-field habitat. We hypothesized that a living mulch would increase the abundance of the aphidophagous community in soybean and suppress A. glycines establishment and population growth. We measured natural enemy and soybean aphid abundance in soybean grown with and without an alfalfa (Medicago sativa L.) living mulch. Soybean grown with an alfalfa living mulch had 45% more natural enemies, A. glycines establishment was delayed, and peak populations were less than on soybean grown without a living mulch. To estimate the impact of natural enemies on A. glycines, plants were artificially infested using cages to exclude natural enemies. Natural enemy abundance within soybean grown without the living mulch was sufficient to delay aphid population growth until more than 30% of the plants were infested with A. glycines. We also observed an impact of alfalfa on the quality of soybean as a host for A. glycines, with reduced reproduction on soybean grown with a living mulch. However, the contribution of predator mortality was responsible for the greatest difference in soybean aphid populations between soybean with and without the living mulch. Our results indicate conserving the natural enemy community before the arrival of A. glycines can delay and suppress A. glycines outbreaks.