Advancing Semiochemical Tools for Mountain Pine Beetle Management: Dendroctonus ponderosae Responses to Saprophytic Fungal Volatiles.

Background/objectives: Within their host trees, mountain pine beetles (MPBs, Dendroctonus ponderosae) interact with many fungal species, each releasing a unique profile of volatile organic compounds (VOCs). The FVOCs released by the two primary symbionts of MPBs, Grosmannia clavigera and Ophiostoma montium, have been found to enhance MPB attraction in the field and laboratory studies. Opportunistic, saprophytic fungal species, such as Aspergillus sp. and Trichoderma atroviride, are also common in MPB galleries and can negatively impact MPB fitness. However, little is known about the FVOCs produced by these fungal species and how they may impact MPB feeding and attraction.

Methods: To address this knowledge gap, we characterized the FVOC profile of T. atroviride, and performed bioassays to test the effects of its FVOCs on MPB attraction and feeding activity.

Results: Our chemical analysis revealed several FVOCs from T. atroviride known to inhibit the growth of competing fungal species and impact subcortical-beetle attraction.

Conclusions: From those FVOCs, we recommended four compounds-2-pentanone, 2-heptanone, 2-pentanol, and phenylethyl alcohol-for use in future field tests as anti-attraction lures for MPBs. In bioassays, we also observed strong MPB repellency from FVOCs released by T. atroviride, as well as the mild effects of FVOCs on MPB feeding activity. Our findings highlight the potential for these FVOCs to be utilized in the development of more effective MPB anti-attractant lures, which are crucial for the monitoring and management of low-density MPB populations.