Oviposition induced indirect defense in sorghum. In: Compendium of papers & abstracts:

Abstract

Plants respond to herbivory through different defensive mechanisms. The induction of volatile emission is one of the important and immediate responses of plants to herbivory. Herbivore attack is known to increase the emission of volatiles, which in turn attracts natural enemies (parasites) to the herbivore-damaged plants. However, the specificity and role of plant volatiles induced during the early phase of attack, i.e. egg deposition by herbivorous insects, and their consequences on insects of different trophic levels remain poorly explored. We investigated behavioural responses of a parasitic wasp, Cotesia flavipes (Cameron) to volatiles of sorghum plants (Sorghum bicolor L), induced by oviposition of the spotted stemborer, Chilo partellus Swinhoe. Herbivore induced plant volatiles were collected from plants exposed to egg deposition by the C. partellus. We found that egg deposition by C. partellus moths on sweet sorghum variety, SSV84 caused emission of volatiles which elicited response in parasitic wasps. In a four-arm olfactometer, the female parasitic wasp, C. flavipes preferred samples containing volatiles from plants with eggs over the ones without eggs. C. flavipes spent significantly more time in the region with volatiles from SSV 84 with eggs as compared to regions with unexposed and solvent controls (P<0.001). The increase in time spent is a positive response, indicating increased attraction of parasitoids to oviposition induced volatiles. EAG active compounds were released in higher amounts from the egg induced headspace samples. Our findings imply that prior to actual feeding damage, egg deposition can induce specific plant responses which, significantly influence members of higher trophic levels. This induction of plant synomones in response to oviposition can be considered as a preventive plant defense strategy that acts prior to herbivory by stemborer larvae.