Can selective insecticides control soybean aphid populations without harming natural enemies?

Aphis glycines Matsumura (Hemiptera: Aphididae) is a pest to soybean in the United States. Broad-spectrum insecticides are successful in preventing damage due to the soybean aphid, but reduce natural enemy communities that are present in the soybean. To reduce the impact of broad-spectrum insecticides on natural enemies, more selective insecticides can be used against A. glycines. If selective insecticides manage the pest without affecting the associated natural enemies, a ‘bioresidual’ of the selective insecticides may be possible. Bioresidual was observed with the use of selective insecticides when applied to control whiteflies, Bemisia tabaci (Hemiptera: Aleyrodidae) in cotton. A bioresidual produces suppression of the pest after the insecticide is no longer present, due to the biocontrol of the pest by the conserved natural enemies. We hypothesize that selective insecticides will provide similar control of soybean aphid as broad-spectrum insecticides, but will not reduce natural enemy populations. We used the following insecticides: esfenvalerate a broad-spectrum insecticide, spirotetramat, imidacloprid, and a combination of spirotetramat and imidacloprid, which represent selective insecticides. The abundance of aphids and natural enemies were measured before and after insecticide application. The insecticides were applied when A. glycines reached the economic threshold. To test for biocontrol, we compared A. glycines on caged and uncaged soybean plants. Our results indicate that the selective insecticides controlled soybean aphid populations at similar levels as the broad-spectrum insecticides. We did not observe a bioresidual as our comparison of caged and uncaged aphid populations suggest that biocontrol of A. glycines did not occur.