Influence of temperature on the reproductive success, brood development and brood fitness of the eastern larch beetle Dendroctonus simplex LeConte

The eastern larch beetle Dendroctonus simplex LeConte colonizes the phloem of tamarack Larix laricina (Du Roi) K. Koch, preferring recently dead or moribund trees weakened by insect defoliation or other factors that predispose trees to beetle attack. Outbreaks of eastern larch beetles are typically localized, of short duration, and collapse when the supply of stressed hosts is exhausted. Although rare, landscape-level outbreaks of eastern larch beetles can occur if large areas of tamarack become stressed. From 2000 onward, an ongoing outbreak of eastern larch beetles in the Great Lakes Region of North America has resulted in extensive mortality to more than 75 000 ha of tamarack forest in Minnesota, U.S.A. This outbreak has no known biotic predisposing factor, such as extensive defoliation. Trends of recent climate warming, however, are suspected to be a contributing factor. Current efforts to model the effects of climate on eastern larch beetle population dynamics are hampered by an absence of data relating beetle developmental biology to temperature. In a laboratory study, we studied eastern larch beetle reproductive success, larval development and offspring fitness at temperatures in the range 9.9-29.4 °C. Offspring production was similar across temperatures. Successful brood development occurred at 9.9 °C, whereas the minimum and optimal developmental temperatures were calculated to be 7.5 and 27.9 °C, respectively. Offspring size and lipid content were maximized between 20 and 22 °C. Our results indicate a potential trade-off between temperatures that maximizes eastern larch beetle offspring fitness versus developmental rate. The implications of such a trade-off are discussed with respect to beetle population dynamics.