Sex pheromone component produced by microbial associates of the forest pestMegaplatypus mutatus

Abstract

AbstractMegaplatypus mutatus(Chapuis) (Coleoptera: Platypodidae) is an ambrosia beetle native to South America that causes economic loss and was recently introduced to Italy, where it attacks and damages live poplar trees. Sulcatol and sulcatone are male‐produced pheromone components involved in the mating process ofM. mutatus. Their relative proportions are highly variable among insects, although the temporal pattern shows that initially only sulcatol is present, and sulcatone increases with time, until they are finally both depleted. Sulcatol and sulcatone may be produced de novo by the beetles, they may be produced by fungi, or both pathways may contribute to their production. Sulcatol is stored in the males’ hindgut but sulcatone is only present in emissions, so there is an oxidation process to transform the alcohol to the ketone before or during pheromone release. It is our hypothesis that fungi associated withM. mutatusare responsible for this process. In this work, we studied a possible contribution of associated microorganisms in the conversion of sulcatol into sulcatone and its consequent role in the temporal release pattern of these sex pheromone components observed in male insects. Moreover, we inhibited the postulated enzymes involved in this pheromone conversion process – 3‐hydroxy‐3‐methyl‐glutatyl‐CoA reductase (HMGR) and P450 enzymes of a fungal strain – and added an antibiotic and a fungicide to the homogenate during sulcatol‐sulcatone conversion. Among the fungal species, particular interest was given toGraphium basitruncatum(Matsush.) Seifert & Okada (Microascales), as it is present in male but not in female exoskeletons and in insect gallery samples, suggesting a possible different role in pherome production, as the male is the pheromone‐producing sex. Several isolated strains were able to convert sulcatol to sulcatone, whereas the fungusG. basitruncatumshowed the highest production of this ketone. Additionally, inhibition of P450 enzymes andHMGRfromG. basitruncatumon this alcohol‐ketone conversion demonstrated thatHMGRis involved in sulcatone generation using sulcatol as precursor, and that P450 enzymes are not. Finally, sulcatone production diminished significantly in homogenized tissues of male and femaleM. mutatusfollowing addition of an antibiotic and a fungicide. The results suggest that fungi associated withM. mutatusare involved in pheromone production.