Building an appetite: Energetic condition and host orientation in the mountain pine beetle

Range expansion of animals has increasingly been attributed to global climate change. Eastward expansion of the mountain pine beetle (Dendroctonus ponderosae; MPB) into Alberta in the early 2000s is a notable case of climate change-induced range expansion. Energy budgeting forces trade-offs between dispersal and host colonization in the MPB, influencing their spread and establishment. Recent studies have attempted to explain the variation in MPB flight; however, much of this variation remains a mystery. It has been hypothesized that MPB may require lipid oxidation through flight exercise in order to respond to the semiochemicals involved in the host colonization process. We tested the effect of energetic condition of female MPB on subsequent response to host volatiles. Female beetles experienced one of three treatments, resulting in varying levels of energetic condition: 1) a 23 h flight period; 2) 23 h at room temperature, but restricted from flying; 3) 23 h at 4°C, and restricted from flying. Following treatment, we assayed individuals for response to host volatiles using a 4-way olfactometer before performing lipid extraction. Beetles with low energetic condition had the highest behavioural response to host volatiles. Increased receptivity of beetles at low energetic states to host volatiles may contribute to flight arrestment in the MPB. These findings may assist in the development and use of models to predict continued spread across the boreal forest.