Olfactory conditioning in mate searching by the parasitoid Aphidius ervi (Hymenoptera: Braconidae)

Learning-induced host preference in male parasitoid wasps as a potential driver of ecological speciation

Ecological speciation via a host shift plays an important role in the diversification of phytophagous and parasitic insects. However, it is not clear how separation is maintained among initial populations in which genetic separation mechanisms are not fully established. Learning-induced host preference in females can contribute to host fidelity and result in a barrier to gene flow in the initial populations. However, the role of males, which also affects gene flow, has been largely unexplored. We examined host preference through induced learning in males, which can contribute to initial population divergence, in the parasitoid wasp, Anisopteromalus calandrae, and two host species, Callosobruchus chinensis and C. maculatus. Behavioural experiments were performed using a four-chamber olfactometer. When wasps were conditioned during the preimaginal and early adult stage without mating experience, no preference was induced regardless of the host species. However, when wasps were conditioned at the early adult stage using the odour of the rearing host and mate reward, preference was induced in both host species. These results demonstrate mate reward learning-induced host preference in males. Interestingly, when the rearing host species and the mating conditioning host species were interchanged, preference was induced only in males conditioned to C. maculatus at mating. Thus, depending on the host species, preimaginal and early adult learning is vital to preference induction. Our results suggest that behavioural change via learning in males plays a more important role in the ecological speciation of phytophagous and parasitic insects than previously recognized.

Bactrocera oleae-induced olive VOCs routing mate searching in Psyttalia concolor males: impact of associative learning

Olfaction is a key sense routing foraging behaviour in parasitoids. Preferences for food, mate and host stimuli can be innate in parasitic wasps. Alternatively, learning-mediated mechanisms play a crucial role. Females of the braconid parasitoid Psyttalia concolor exploit olfactory cues arising from tephritid hosts and related microhabitats. However, little is known on the olfactory stimuli routing males searching for mates. In this study, we focused on the attractiveness of Bactrocera oleae-induced olive volatiles towards P. concolor males. Furthermore, we evaluated learning occurrence in virgin males, when trained for selected unattractive volatile organic compounds (VOCs) associated with mate rewards. (E)-β-Ocimene, α-pinene and limonene attracted virgin males in Y-tube bioassays. Unattractive VOCs evoked positive chemotaxis after associative learning training. P. concolor males exposed to VOCs during a successful or unsuccessful mating, showed short-term preference for these VOCs (<1 h). However, memory consolidation was strictly dependent on reward value. Indeed, males experiencing a successful mating showed a fast consolidation into protein dependent long-term memory, appearing after 24 h. On the other hand, males experiencing a less valuable training experience (i.e. unsuccessful courtship), did not show consolidated memory after 24 h. Overall, our findings suggest that P. concolor virgin males may exploit VOCs from the host microhabitat to boost their mate searching activity, thus their reproductive success. However, since learning is a costly process, P. concolor males retained durable memories just in presence of a valuable reward, thus avoiding maladaptive behaviours.

Does sex-biased dispersal account for the lack of geographic and host-associated differentiation in introduced populations of an aphid parasitoid?

Host recognition and use in female parasitoids strongly relies on host fidelity, a plastic behavior which can significantly restrict the host preferences of parasitoids, thus reducing the gene flow between parasitoid populations attacking different insect hosts. However, the effect of migrant males on the genetic differentiation of populations has been frequently ignored in parasitoids, despite its known impact on gene flow between populations. Hence, we studied the extent of gene flow mediated by female and male parasitoids by assessing sibship relationships among parasitoids within and between populations, and its impact on geographic and host-associated differentiation in the aphid parasitoid Aphidius ervi. We report evidences of a high gene flow among parasitoid populations on different aphid hosts and geographic locations. The high gene flow among parasitoid populations was found to be largely male mediated, suggested by significant differences in the distribution of full-sib and paternal half-sib dyads of parasitoid populations.

Male-male sexual behavior in the parasitic wasp Psyttalia concolor

The role of male-male courtship in parasitic Hymenoptera is poorly known. A laboratory study was conducted to assess if Psyttalia concolor (Szépligeti) (Hymenoptera: Braconidae) male courtship can be affected by a previous experience in courting young conspecifics of both sexes. Two experiments were performed to evaluate the effect of experience in courting young wasps on both male courtship and male-male competition behavior. Results showed that a courting experience on both sexes can modify some sexual traits in a P. concolor male, without affecting its success in mating. When approaching virgin females, a P. concolor male that had a previous courtship experience with young wasps of either sex showed shorter latency times, more wing fanning, and longer courtship durations with respect to the control male. The hypothesis that a previous courting experience may allow a P. concolor male to refine its courtship behavior and to enhance courtship intensity in subsequent encounters with females was discussed.