Abstract
Bark-beetle associated tree-mortality has serious negative impacts on biodiversity & carbon sequestration in forests. Historically, the mountain pine beetle (MPB) range in Canada has been restricted to British Columbia and western Alberta. However, due to climate change and other disturbances, the MPB range is now expanding eastwards, into the boreal forest. Beetle populations on the frontier of this range currently exist at low densities and interact differently with their semiochemical landscape compared to high-density populations and, therefore, are more challenging to monitor using conventional tools developed for high-density populations. The development of effective MPB detection tools specific to low-density populations is crucial for the monitoring and management of MPB populations on the frontier of range expansions. Trees under biotic stress release ‘stress volatile chemicals’ (SVCs) that are not released otherwise. SVCs may provide the necessary chemical cues for mountain pine beetles (MPB) to locate the most suitable (i.e., less defended) hosts. Similarly, the potential contribution of fungal volatiles (FVOCs) to MPB attraction is largely unexplored. In nature, we typically find trees infected by the fungal associates of MPB after unsuccessful host colonization; however, due to unusual climate patterns, the numbers and availability of such trees have dramatically increased in recent years. Low-density MPB populations will likely target these trees; thus, fungal volatiles released from such trees will likely improve host location by MPB. Previous studies have: (1) Characterized the volatile profiles of MPB symbiotic fungi, (2) Characterized host stress volatile profiles in response to inoculation by MPB symbiotic fungi, and (3) found strong MPB attraction to FVOCs emitted by their symbiotic fungi using olfactometer assays. However, interactions between these groups of volatile compounds and mountain pine beetle have yet to be tested in the field. Our primary goal is to determine the feasibility of using SVCs and fungal volatiles to enhance the efficacy of mountain pine beetle attractants in low-density populations by identifying volatiles that increase MPB attraction to pheromones compared to conventional traps. Overall, we've observed that FVOCs and SVCs alone do not attract low-density MPB populations in the field. We also observed possible synergistic effects between key FVOCs and MPB pheromones on MPB attraction. We identified key FVOCs as 2-methyl-1-butanol and 2-methyl-2-butanol, however, the repeatability of these findings is unclear. Therefore, further research is needed before these chemicals can be implemented as semiochemical tools for low-density MPB population monitoring.