Forest Insect Population Dynamics Outbreaks And Global Warming Effects PDF Download

Insects and other biotic agents are a major source of forest disturbance in eastern North America, with the potential for widespread ecological, economic, and social consequences. Mitigating effects of pest outbreaks requires knowledge of the factors that regulate their populations, and for insects and other ectotherms, temperature is one of the most important of these factors. Here, we tested a number of hypotheses focusing on the effects of different temperature regimes on population level processes. For each chapter we used the southern pine beetle (Dendroctonus frontalis), one of the most destructive forest insect pests, as a model species. This insect has undergone important changes in population abundance at both the northern and southern extremes of their distribution. We first investigated the influence of cold temperatures, which have become increasingly important as populations expand northward. We specifically examined the influence of overwintering temperatures on the population life stage structure. We hypothesized that colder temperatures could lead to a convergence of the life stage structure, and this could subsequently produce a high level of synchrony in their flight phenology the following spring. Results from a series of experimental tests, as well as theoretical explorations using development rate models supported this hypothesis; however, field observations were mixed. The second set of hypotheses focused on the effects of high temperature exposure on southern pine beetle populations. As climate change alters global surface temperatures, the occurrence of heat waves are predicted to increase. We analyzed longterm (74 years) temperature records to characterize high temperatures events in the southern pine region. This information was paired with a series of experimental tests of high temperature tolerance in the southern pine beetle, to determine how extreme high temperatures may be impacting southern populations. We experimentally tested both acute and chronic high temperature exposure in northern and southern populations of the beetle. Results from the climate analysis showed no significant change in yearly maximum temperatures throughout the southern pine region, and model results indicated that the characteristics of both common and rare heat waves had not changed over the 74 year study period. Experimental tests of high temperature exposure in southern pine beetle larvae showed a greater than expected tolerance to thermal extremes, and these results were consistent in both northern and southern populations. Overall, we conclude that high temperatures do not explain recent changes in southern pine beetle populations in their historic southern habitat.