Influence of Semiochemical Cues on Mountain Pine Beetle Flight and Subsequent Effect of Flight on Host Colonisation Processes

The mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), is an aggressive pine pest in western North America. This beetle undergoes cyclical population outbreaks, and in the most recent outbreak the beetle expanded its range to the north and east. During this range expansion, beetles breached the Rocky Mountains and entered North-Central Alberta. The spread of the mountain pine beetle into Alberta resulted in colonization of a new pine host, jack pine (Pinus banksiana). Dispersal is an extremely important part of mountain pine beetle ecology, yet it is the least understood part of the life cycle. Mountain pine beetle exhibit stratified dispersal, this dispersal type is characterized by large variation in dispersal distance among individuals within the population. Some of this variation can be explained by beetle physiological condition, stand density or abiotic environmental factors; however, these factors do not explain all the variation exhibited. Using computer-linked flight mills I tested how olfactory cues that beetles encounter in the environment contribute to flight variation through an influence on beetle flight propensity and capacity. Further, I tested how this large degree of variation in flight distance impacts subsequent life history events in the mountain pin beetle. These experiments led to six major findings: (1) Exposure to host volatiles before flight interacts with beetle pre-flight weight to influence flight of female but not male beetles; (2) Female beetles fly shorter distances when exposed to volatiles from non-host angiosperms during flight than in clean air; (3) Exposure to aggregation pheromone prior to flight results in increased flight distance and velocity in female beetles; (4) There is a trade-off between host colonization and flight, as beetles that lose more weight during flight are less likely to enter a host; (5) Percent weight lost during flight and distance flown by female beetles influences subsequent production of the aggregation pheromone, trans-verbenol; and (6) Male beetle condition prior to flight but not energy used during flight influences exo-brevicomin production. This study is the first to show that semiochemical cues not only influence flight orientation, but also flight capacity of the mountain pine beetle. Further, the distance flown by individual beetles influences the subsequent host colonization processes of mountain pine beetle, which could potentially reveal mechanisms behind the well-documented flight polyphenisms in this species. These novel results give insight into the highly variable flight behaviour of the mountain pine beetle.

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