Energy Use During Flight Impacts Semiochemical Response in the Mountain Pine Beetle.

Abstract

Global climate change drives the range expansion of various taxa, including the mountain pine beetle (Dendroctonus ponderosae; MPB). Dispersal and host colonization dictate spread and establishment of MPB populations, but this comes with energetic, time, risk, and opportunity costs. As MPB exhibit continuous flight polyphenisms, researchers have proposed that energy use during flight may trigger responsiveness to the semiochemicals that orchestrate the colonization of host pine trees, but this effect has not been demonstrated empirically. Here, we test the hypothesis that flight exercise impacts subsequent behavioral response to semiochemicals in two olfactometer experiments that simulate 1) female beetle pioneer response to host volatiles and 2) male and female joining beetle response to host volatiles and the female-produced aggregation pheromone, trans-verbenol. We also assess antennal response of female beetles to α-pinene post-flight in an electroantennogram bioassay. Female MPB with low condition due to energy expenditure responded strongly to host semiochemicals post-flight. The antennal response of female MPB to the host volatile α-pinene increased with relative lipid content of beetles. Male behavioral response to semiochemicals was not influenced by body condition or exercise by flight. The effect of flight and body condition on orientation to semiochemical cues may influence individual dispersal patterns. These findings should be considered in the refinement of dispersal models that incorporate individual variability to predict spread of MPB in its expanded range.