Maize plants sprayed with either jasmonic acid or its precursor, methyl linolenate, attract armyworm parasitoids, but the composition of attractants differs

Treatment of both uninfested and armyworm-infested maize plants with jasmonic acid (JA) is known to attract the parasitic wasp, Cotesia kariyai Watanabe (Hymenoptera: Braconidae). Here, we show that treatment with a methyl ester of a JA precursor, methyl linolenate (MeLin), also causes maize plants to attract this wasp, yet does not cause elevated levels of endogenous JA. The volatile chemicals emitted from either infested or uninfested maize plants treated with MeLin were qualitatively and quantitatively different from those emitted from JA-treated plants. Among compounds emitted from MeLin-treated plants, alpha-pinene and menthol attracted wasps in pure form in a two-choice test using a choice chamber. A mixture of methyl salicylate, alpha-copaene, and beta-myrcene also attracted wasps. In contrast, (Z)-3-hexenyl acetate was among the main attractants for C. kariyai in JA-treated plants. These data show that in addition to JA, MeLin also has the potential to increase the host-finding ability of C. kariyai, but that the composition of attractants they induce differs.