Tracing potential pinewood nematode semiochemicals emitted by its insect vector Monochamus galloprovincialis

Monochamus spp., commonly known as sawyer beetles (Coleoptera: Cerambycidae), are conifer wood borers capable of causing decreases in wood value of up to 40 % due to the tunnels built by their larvae in freshly cut logs. However, the greatest impact on pine forests comes from their phoretic association with the pinewood nematode (PWN), Bursaphelenchus xylophilus, an aggressive phytoparasite that causes rapid pine decline in Asian and European forests (Portugal and Spain). Beetles become vectors for the PWN during the callow adult stage while still inside the pupal chambers, deep in infected pine wood. The presence of teneral adults in dead infected wood stimulates PWN's transition from the propagative to the dispersive stage (Dauer juveniles), involving extensive morphological changes. The colonized beetles transport PWNs in their respiratory system (trachea) and transmit them to uninfected pines during maturation feeding. The interaction between these two different organisms is still not completely understood, but volatile compounds are believed to mediate their communication. The present work aimed at profiling the volatiles emitted by different life stages of the European pine sawyer beetle Monochamus galloprovincialis through solid-phase microextraction (SPME) using sorbent packed tubes to capture emitted volatiles and thermal desorption coupled to gas chromatography–mass spectrometry (TD-GC-MS) for compound identification. Several volatiles were found to be constitutively emitted by the different insect life stages (larvae, pupae, and callow adult males and females); however, seven compounds were found in callow adults only, e.g., C12 and C13 aliphatic alkanes, C7 and C8 aliphatic aldehydes, or the ketone 6-methyl-5-hepten-2-one. Further studies will focus on their attractiveness to the PWN. This knowledge will contribute to developing innovative strategies to break the intricate cycle of pine wilt disease caused by the PWN.

This research was partly funded by the EU through project PurPest, grant agreement 101060634 (https://doi.org/10.3030/101060634) and PWNUK2022.