Parasitoid exploitation of the seasonal variation in host plant volatile emission for herbivore location

Abstract

AbstractVolatile compounds from the apple, Malus domestica Borkh. (Rosaceae), change considerably as the season progresses, and this is successfully exploited by the female codling moth Cydia pomonella L. (Lepidoptera, Tortricidae), as it searches for oviposition sites. In this study, we investigated the effect of seasonal emissions of apple fruit volatiles on the host location behaviour of a parasitoid of the codling moth larvae, Hyssopus pallidus (Askew) (Hymenoptera: Eulophidae). In dual choice olfactory bioassays, the behaviour of the parasitoid in response to apple cues was observed over the complete 2003 growing season. Our results show that codling moth infested apples evoked a strong response from the parasitoid at the beginning of the season, until July. Then, attraction dropped drastically, increasing again at the beginning of August. At the end of the growing season, just prior to harvest, infested apples hardly evoked any behavioural response. Interestingly enough, mid‐season emissions of healthy apples were per se attractive to the parasitoid, and even preferred over volatiles from infested apples. Simultaneous volatile collections from healthy apples on twigs in the field were analysed throughout the season, showing that the overall quantity of headspace volatiles peaks at the beginning of June and mid‐August. The seasonal volatile emission is correlated with the behaviour of the parasitoid during the fruit ripening stage. The results are discussed in relation to the use of H. pallidus as a potential biocontrol agent, in order to enhance current integrated pest management (IPM) programs.