Plant-odour mediates parasitoid host handling and oviposition in an endophytic tritrophic system

Abstract

The final steps of a parasitoid host selection process, host handling and oviposition, might be affected by the habitat cues to which parasitoids are exposed, and not only by the host itself. The habitat-related factors promoting parasitoid host-handling and reproductive success were investigated in a laboratory colony of Hyssopus pallidus, a larval parasitoid of the codling moth, Cydia pomonella, an important pest of apple. Parasitoid host handling was addressed in computer-monitored behavioural bioassays during 8 h. Naive females showed more intensive host handling behaviour (frequent host examination) when offered host larvae in combination with apple fruits or in combination with an artificial diet devoid of fruit material than when offered host larvae alone. The exposure of parasitoids to fresh apple during host handling resulted in an enhanced behavioural response equivalent to that one obtained by giving an oviposition experience prior to the bioassay. The progeny produced by parasitoids exposed to plant cues for 8 h was almost double that of parasitoids exposed to artificial diet or no cues. Parasitoids exposed to no cues produced the same amount of progeny than parasitoids exposed to apple cues only with an increased time of exposure (32 h). The data demonstrate that the odour emitted by the host-food plant represent not only a habitat location signal, but triggers and enhances parasitoid host handling behaviour and reproductive success.