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

Abstract

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.

Chemotactic responses and parasitism of Trichogramma pretiosum after successive generations in Spodoptera frugiperda

“…Our results showed that the multiplication of this parasitoid by successive generations in the target host may affect its behavior, possibly leading to a greater potential for parasitism of the target host in the field. It is also worth considering that learning can also occur in the adult stage of the parasitoid (Keaton & Woods, 2016; Vargas et al., 2017; Giustina et al., 2022; Gonthier et al., 2022). Thus, because the response to the extracts was similar to that observed in eggs, the presence of these odors after parasitoid emergence (imaginal conditioning) could be an alternative for T. pretiosum learning before release, possibly optimizing its search and parasitism process in S. frugiperda eggs.…”

“…Regarding the host in which parasitoids develop, Gonthier et al. (2022) observed that rearing Trichogramma achaeae Nagaraja & Nagarkatti, currently used for biological control of Tuta absoluta (Meyrick) in Europe (Desneux et al., 2021), strongly increased the arrestment time on eggs in this host. Despite the importance of T. pretiosum in the biological control of S. frugiperda , the effect on the foraging behavior and the biotic potential of females after successive generations in S. frugiperda eggs is not known.…”