Methyl salicylate reduces populations of the soybean aphid, Aphis glycines Matsumura, through the attraction of natural enemies

Methyl salicylate (MeSA), an herbivore-induced plant volatile, has been shown to attract natural enemies, repel herbivores, and reduce herbivore population growth rates. In this study, MeSA was tested in organically managed soybeans for its ability to attract natural enemies of the soybean aphid, Aphis glycines Matsumura, and for its direct effects on soybean aphid fecundity and population growth rates. Sticky-card traps baited with MeSA lures measured the attraction of natural enemies to MeSA, and soybean aphid populations were monitored in MeSA treated areas. Additionally, clip cage and exclusion cage studies were conducted to determine MeSA's effects on soybean aphid fecundity and population growth rates in the absence of natural enemies. Traps baited with MeSA caught significantly greater numbers of two natural enemy taxa, syrphid flies (Diptera: Syrphidae) and green lacewings (Neuroptera: Chrysopidae). Abundances of soybean aphids were significantly lower in treated plots and in open cages treated with MeSA, however, abundances did not differ between treated and untreated closed cages. Additionally, MeSA had no effect on soybean aphid fecundity in clip cages, suggesting that the mechanism by which MeSA reduces soybean aphid abundance is the attraction of natural enemies. Synthetic MeSA may be instrumental in enhancing biological control of the soybean aphid, particularly in organic, soybean fields.