Male and female Trybliographa rapae (Hymenoptera: Figitidae) behavioural responses to food plant, infested host plant and combined volatiles

Parasitoids reach maximum reproductive success when responding to plant stimuli associated with food and host. We investigated the attraction of the parasitic wasp Trybliographa rapae Westwood (Hymenoptera: Figitidae) to volatiles emitted from plants infested by the cabbage root fly Delia radicum L. (Diptera: Anthomyiidae), as well as to volatiles from a nectar food plant. Behavioural choice tests showed that male parasitoids were not attracted to any volatiles from plants infested by D. radicum or from nectar plants, while females showed clear attraction to both volatile sources. Newly emerged females preferred combined volatiles of host and food plants over those from only the host plant, whereas older females showed no differences in attraction. This suggests that intercropping attractive flowers with host plants could potentially be used to recruit newly emerged parasitoids from surrounding fields while older parasitoids invest more energy in host allocation than in additional food search. Volatiles from a whole infested plant were preferred over those emitted from separated above- and belowground parts from infested plants, indicating that female parasitoids recognize a synergistic effect from plant volatiles. It is important to consider the availability of both energy and host resources for parasitoids when designing an eco-compatible management of a vegetable crop system.