The Evolution of Pheromone Communication in the Genus Leptopilina (Hymenoptera: Figitidae), a Parasitoid of Drosophila.

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The origin and evolution of pheromones is one of the major questions in chemical ecology. In recent years funding by the DFG gave me the opportunity to study the chemical ecology of the parasitoid wasp Leptopilina heterotoma (Hymenoptera, Figitidae), a larval parasitoid of Drosophila. The species provides a rare case of threefold semiochemical parsimony and prime example of insect pheromone evolution from a non-communicative compound. We could show that females of L. heterotoma produce (-)-iridomyrmecin (and minor amounts of some other iridoid compounds) and use it as a defensive allomone against predators. Furthermore, females of L. heterotoma use (-)-iridomyrmecin as a chemical cue to avoid host patches already exploited by con- and heterospecific females. And finally, the females use (-)-iridomyrmecin as the major component of their female sex pheromone. (-)-iridomyrmecin thus most probably originally evolved for defensive purposes and only became a pheromone later on. This project continues and expands the studies done in my current DFG project. In the first part of the project I will use a comparative approach to identify the use of iridoids as defensive allomones, chemical cue to avoid competition among females, and sex pheromone in several species of Leptopilina and outgroup species. I will combine these data with a molecular phylogeny to shed light on the evolution of the chemical ecology of these species. In the second part of the project I will investigate the stereospecific detection of iridomyrmecin. The molecule of iridomyrmecin has four chiral carbon atoms and thus 16 stereoisomers of iridomyrmecin exist. My behavioral experiments have demonstrated, that males of L. heterotoma can discriminate between (-)-iridomyrmecin and (+)-iridomyrmecin. Using single sensillum recordings, I aim to identify the sensilla on the antennae of L. heterotoma sensitive to (-)-iridomyrmecin and to systematically map the olfactory sensilla on the antenna of males and females. Additionally I will analyze the transcriptome of the antennae of males to identify putative ORs.In addition the enantiospecific detection by the receiver, (-)-iridomyrmecin has to be biosynthezised enantiospecifically by the sender. In the third part of the project I will start to elucidate the biosynthesis pathway of (-)-iridomyrmecin in L. heterotoma. I will use labelled precursors to confirm that iridoid synthesis in L. heterotoma follows the same principal pathway as found in other insects. In the second step I will search the transcriptome of the mandibular gland of L. heterotoma for candidate iridoid synthases.I am convinced that the results from this project will significantly contribute to our understanding of the evolution of chemical communication in insects.