Behavioural ecology of interactions between trees and bark beetles mediated by climate

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Interactions between herbivorous insects and their host plants are among the most common and potent interactions in terrestrial ecosystems. A recent example is the outbreak of mountain pine beetles (MPB), Dendroctonus ponderosae, a bark beetle that has killed hundreds of millions of mature pine trees. My research program will investigate the state-dependent reproductive tactics of individual bark beetles in the context of the dynamic habitat quality of their host trees. While it has long been observed that MPB kill primarily large-diameter pines during outbreaks, the causes of this pattern are unresolved. Theory predicts that defence allocation by plants will vary non-linearly with growth rate and tree height. Using meta-analyses and empirical studies, we will quantify the relationships between tree diameter, height, age and growth rate (correlated traits of interest to industry) and the quantity and quality of inner bark (phloem) in which beetles feed and reproduce. Our empirical work will focus on the effects of water stress (spatially and historically) and tree age in pine within and outside the historical range of MPB and consider their contributions to MPB outbreaks. Given these tree processes, we will examine how tree traits influence tree choice and reproductive strategies of bark beetles according to beetle state. In particular, we will test whether MPB use tree acoustic emissions to predict the ability of the tree to defend itself against beetle attack. To examine the apparent preference of MPB for large diameter trees, we will determine encounter rates and reproductive success of beetles in trees that vary in diameter. Using our understanding of tree trait dynamics and state-dependent reproductive behaviour of bark beetles, we will test their contributions to beetle population dynamics with empirical studies and models. This research program brings new insights from behavioural ecology to better understand bark beetle ecology, a key taxon affecting Canada's forests. This work is critical for anticipating the effects of bark beetles and other forest insects in a changing climate.