Managing soybean aphids with selective insecticides results in a bioresidual

Aphis glycines Matsumura (Hemiptera: Aphididae) is a pest to soybean in the United States. Broad-spectrum insecticides are successful in preventing damage caused by 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 provides suppression of the pest after the active ingredient of 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, which in turn will result in a bioresidual. We used the following insecticides: esfenvalerate a broad-spectrum insecticide, spirotetramat, imidacloprid, and a combination of spirotetramat and imidacloprid, which represent selective insecticides. We conducted a cage study where a caged and uncaged plant were artificially infested with ten aphids per plant after insecticide application, and then monitored from 10 to 19 days after treatment (DAT), and from 18 to 27 DAT. We used a Biocontrol Services Index (BSI) to determine if a bioresidual was present in the treatments. Our results indicate that selective insecticides do provide a bioresidual effect in soybean.