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

The final steps of a parasitoid host selection process, host handling and o viposition, might be affected by the habitat cues to which parasitoids are exposed, and not only by the host itself. The habitat-related factors promo ting parasitoid host-handling and reproductive success were investigated in a laboratory colony of Hyssopus pallidus, a larval parasitoid of the codli ng moth, Cydia pomonella, an important pest of apple. Parasitoid host handl ing was addressed in computer-monitored behavioural bioassays during 8 h. N aive females showed more intensive host handling behaviour (frequent host e xamination) when offered host larvae in combination with apple fruits or in combination with an artificial diet devoid of fruit material than when off ered host larvae alone. The exposure of parasitoids to fresh apple during h ost handling resulted in an enhanced behavioural response equivalent to tha t one obtained by giving an oviposition experience prior to the bioassay. T he progeny produced by parasitoids exposed to plant cues for 8 h was almost double that of parasitoids exposed to artificial diet or no cues. Parasito ids 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 no t only a habitat location signal, but triggers and enhances parasitoid host handling behaviour and reproductive success.