Modeling mountain pine beetle phenological response to temperature

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Proc. of a Mountain Pine Beetle Symposium: Challenges and Solutions


Shore T.

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Maintaining an adaptive seasonality, with life cycle events occurring at appropriate times of year and in synchrony with ephemeral resources, is a basic ecological requisite. For poikilothermic organisms, phenology is largely determined through adaptive evolution with the prevailing climate, and in particular, annual temperature cycles. In addition to the direct effect of temperature, most temperate region insects have physiological mechanisms (e.g., diapause) that help to maintain an adaptive seasonality. The mountain pine beetle (Dendroctonus ponderosae Hopkins), however, exhibits no obvious manifestations of diapause. This has led to the ecologically important question: How is an appropriate seasonality maintained in the mountain pine beetle without the synchronizing influence of diapause? In answer to this basic question, we briefly review the mathematical relationship between environmental temperatures and developmental timing and discuss the consequences of viewing these models as circle maps from the cycle of oviposition dates and temperatures of one year to oviposition dates for subsequent generations. Univoltinism, associated with reproductive success for the mountain pine beetle, is related to stable fixed points of the developmental circle map. Univoltine fixed points are stable and robust in broad temperature bands, but lose stability suddenly to maladaptive cycles at the edges of these bands. This leads to the obvious observation that temperatures (weather) can be too cold for the mountain pine beetle to thrive, as well as the less obvious implication that it can also be too warm. These results are placed in an ecological and management context by relating adaptive seasonality to outbreak potential. The relationship between outbreak potential and temperature is further considered in view of climate change (i.e., global warming). We briefly note the potential for global warming to intensify outbreak characteristics in the current range of mountain pine beetle, as well as promote invasion into new habitats, such as the high elevation pines and northern range expansion into Canadian jack pine.

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