Herbivore-induced plant volatiles enhance field-level parasitism of the mirid bug Apolygus lucorum

Abstract

In China, the braconid wasp Peristenus spretus Chen & van Achterberg (Hymenoptera: Braconidae) is a native endoparasitoid of the mirid bug Apolygus lucorum (Meyer-Dür) (Hemiptera: Miridae). Castor bean (Ricinus communis L.) is a preferred host plant of A. lucorum, and P. spretus adults are attracted to its herbivore-damaged flowering plants. Here, we used headspace collection to sample the volatiles emitted by A. lucorum-damaged flowering R. communis plants, and employed gas chromatography-electroantennography (GC-EAD) to identify two electrophysiologically-active compounds. Active compounds were identified as m-cymene and 4′-ethyl-acetophenone. Electrophysiological activities were confirmed by EAG, with a gradient of five doses of each compound eliciting significant antennal responses. Next, in Y-tube olfactometer bioassays, female P. spretus were attracted to two synthetic volatile compounds at two different concentrations (10 mg/ml and 100 mg/ml). Under field conditions, A. lucorum parasitism rates – as recorded in volatile-baited barrel traps – for the two compounds were significantly higher than those for mineral oil (control). Our findings emphasize the important role of herbivore-induced plant volatiles in the P. spretus host selection process, and provide a potential way to enhance in-field parasitoid populations and improve biological control of A. lucorum.