Relative importance of host and plant semiochemicals in the foraging behavior of Trichogramma achaeae, an egg parasitoid of Tuta absoluta

Herbivore-induced plant volatiles (HIPVs) and host sex pheromones are important semiochemicals used by natural enemies to locate prey or hosts. The egg parasitoid Trichogramma achaeae Nagaraja & Nagarkatti has recently shown potential for use as a biological control agent of Tuta absoluta (Meyrick), a key pest of tomato crops worldwide. In this study, we used olfactometer tests to examine the behavioral response of T. achaeae females to T. absoluta sex pheromone or to HIPVs produced by tomato plants infested with T. absoluta eggs or larvae. Our results showed that T. achaeae was attracted to T. absoluta sex pheromone. Parasitoids were also innately attracted to volatiles produced by tomato plants, whether uninfested or infested. However, parasitoids could not distinguish between volatiles from uninfested or T. absoluta-infested tomato plants. We characterized the headspace volatiles of tomato plants used in the olfactometer tests and found out that oviposition and larval feeding by T. absoluta significantly enhanced HIPV emission. This study suggests that the sex pheromone of T. absoluta is a potential tool to manipulate the behavior of T. achaeae and improve its attraction to the tomato crop. The analysis of volatiles released by tomato plants, either infested or uninfested, coupled with the response of T. achaeae in the olfactometer tests was consistent with what was expected in terms of the foraging behavior of a generalist parasitoid. The results and implications are further discussed in the context of sustainable T. absoluta management.