Conservation biological control aims to enhance natural enemy populations in crop habitats, e.g. by providing flowering plants as food resources. Suitable flower species must enhance the survival and fecundity of natural enemies but in addition they also need to be highly attractive and thus frequently visited. To date, few examples exist that have considered both criteria. In this study, we tested the effects of the flowering plants alyssum (Lobularia maritima), buckwheat (Fagopyrum esculentum), French marigold (Tagetes patula) and sweet basil (Ocimum basilicum) on the fecundity and olfactory attractiveness of the egg parasitoid Trissolcus basalis, an important biological control agent of the stink bug Nezara viridula. Our results showed that access to buckwheat and basil flowers increased the parasitoid offspring. However, in olfactometer experiments where T. basalis was allowed to choose between flowering and non-flowering plants, only buckwheat floral scent was attractive. Headspace analyses of the odour emitted by the four plant species revealed very distinct profiles with little overlap in compounds. Buckwheat floral scent was characterized by an unpleasant smell for the human nose due to the presence of short-chain carboxylic acids. Headspace extracts of buckwheat flowers and a blend of six buckwheat plant volatiles consisting of butanoic, 2-methylbutanoic, 3-methylbutanoic and pentanoic acids, (Z)-3-hexenyl acetate and α-farnesene were significantly attractive in olfactometer bioassays. Furthermore, electrophysiological experiments showed most of these compounds elicited significant responses in T. basalis antennae. Integrating chemo-ecological methods into conservation biological control allowed us to identify a potential resource plant and attractive compounds for field studies

Animals can adjust their behaviour according to previous experience gained during foraging. In parasitoids, experience plays a key role in host location, a hierarchical process in which air-borne and substrate-borne semiochemicals are used to find hosts. In nature, chemical traces deposited by herbivore hosts when walking on the plant are adsorbed by leaf surfaces and perceived as substrate-borne semiochemicals by parasitoids. Chemical traces left on cabbage leaves by adults of the harlequin bug (Murgantia histrionica) induce an innate arrestment response in the egg parasitoid Trissolcus brochymenae characterized by an intense searching behaviour on host-contaminated areas. Here we investigated whether the T. brochymenae response to host walking traces left on leaf surfaces is affected by previous experience in the context of parasitoid foraging behaviour. We found that: 1) an unrewarded experience (successive encounters with host-contaminated areas without successful oviposition) decreased the intensity of the parasitoid response; 2) a rewarded experience (successful oviposition) acted as a reinforcing stimulus; 3) the elapsed time between two consecutive unrewarded events affected the parasitoid response in a host-gender specific manner. The ecological role of these results to the host location process of egg parasitoids is discussed.