Odor learning improves efficacy of egg parasitoids as biocontrol agents against Tuta absoluta

Trichogramma spp. (Hymenoptera: Trichogrammatidae) are generalist egg parasitoids widely used as biological control agents, yet with limited efficacy against Tuta absoluta (Meyrick; Lepidoptera: Gelechiidae), a key pest of tomato. Olfactory cues related to the host-plant complex influence the searching behavior in parasitoids. Studies have shown that female Trichogramma spp. can learn odor cues affecting their preference. We assessed if learning increases the response to tomato odor and whether it improves the parasitism rate of Trichogramma achaeae , Trichogramma evanescens, and Trichogramma dendrolimi . The parasitoids were either naive, reared for one generation on T. absoluta eggs, or conditioned associatively with an oviposition experience on a factitious host in the presence of tomato odor. Subsequently, their arrestment response (searching time) to T. absoluta -infested tomato leaves was observed in a static four-chamber olfactometer. Rearing the parasitoids on T. absoluta increased the arrestment time of T. dendrolimi strongly and that of T. evanescens slightly but not that of T. achaeae . In contrast, oviposition experience on a factitious host with the tomato odor (leaves or extract) increased the searching time of T. achaeae and T. evanescens strongly but did not improve the response of T. dendrolimi. Concerning parasitism improvement, only T. achaeae showed an increased parasitism rate after associative learning. Hence, the learning capacity of T. achaeae should be further explored to improve its biological control efficacy against T. absoluta .