Where you come from matters: temperature influences host-parasitoid interaction through parental effects

Temperature alters host suitability for parasitoid development through direct and indirect pathways. Direct effects depend on ambient temperatures experienced by a single host individual during its lifetime. Indirect effects (or parental effects) occur when thermal conditions met by a host parental generation affect the way its offspring will interact with parasitoids. Using the complex involving eggs of the moth Lobesia botrana as hosts for the parasitoid Trichogramma cacoeciae, we developed an experimental design to disentangle the effects of (1) host parental temperature (temperature at which the host parental generation developed and laid host eggs) and (2) host offspring temperature (temperature at which host eggs were incubated following parasitism, i.e. direct thermal effects) on this interaction. The host parental generation was impacted by temperature experienced during its development: L. botrana females exposed to warmer conditions displayed a lower pupal mass but laid more host eggs over a 12-h period. Host parental temperature also affected the outcomes of the interaction. Trichogramma cacoeciae exhibited lower emergence rates but higher hind tibia length on emergence from eggs laid under warm conditions, even if they were themselves exposed to cooler temperatures. Such indirect thermal effects might arise from a low nutritional quality and/or a high immunity of host eggs laid in warm conditions. By contrast with host parental temperature, offspring temperature (direct thermal effects) did not significantly affect the outcomes of the interaction. This work emphasises the importance of accounting for parental thermal effects to predict the future of trophic dynamics under global warming scenarios.