Temperature influences on phenology and population growth of mountain pine beetle populations in Northern Colorado

The mountain pine beetle (Dendroctonus ponderosae Hopkins) has become a prominent forest pest in lodgepole pine stands on the west and east sides of the Continental Divide in Northern Colorado. With over two million acres of trees killed since 1996, understanding populations in Colorado has become critical. The mountain pine beetle spends the majority of its life under the bark of its host tree. As a result of being poikilotherms, temperatures under the bark, as well as air temperatures, are critical for beetle survival during larval development and eventual adult emergence. Temperatures above given thresholds during development allow adult beetles to emerge synchronously, known as "adaptive seasonality", and hence, successively overcome the defense mechanisms of the tree. Multiple models have been developed and tested to determine what temperatures allow for synchronous emergence. Often the models do not accurately predict adaptive seasonality for areas in Colorado, especially at high elevations where lodgepole pines are found and beetle outbreaks have been documented. Furthermore, the most recent model, the phenology growth rate model (PGRM), links adaptive seasonality to growth rate, taking into account area affected. By finding the ratio of area attacked in one year to the area attacked the previous year, observed growth rates were measured for Grand County. This study used larvae, callow adults, and adult emergence data from plots in FEF and Cameron Pass to compare predictions from the PGRM to observed values. Although the model did not accurately predict growth rates or adaptive seasonality for populations in Colorado, additional knowledge on beetle life cycle timing and duration in relation to phloem and air temperatures were evaluated for the populations. Adjusting model parameters, combined with additional studies on beetle phenology and genetics, will provide supplementary information necessary for developing a model that will accommodate the specific needs of beetle populations in northern Colorado.