Developmental thresholds of eastern larch beetle Dendroctonus simplex LeConte

Previously classified as non-aggressive, eastern larch beetle Dendroctonus simplex LeConte has been in outbreak phase in Minnesota, USA for the past 21 years, affecting ~270,000 ha of tamarack forest. Until recently, it was thought D. simplex was a strictly univoltine bark beetle with an obligate overwintering reproductive diapause. A warming climate, however, has increased the number of degree days suitable for beetle development. Fieldwork completed in 2012 identified a second generation of D. simplex within a single summer, indicating bivoltinism can occur within the species. Laboratory experiments have demonstrated reproductive success of non-overwintered beetles as well as identified minimum and optimal developmental temperatures for eastern larch beetle. The temperature thresholds that govern progression from one life stage to the next are not yet understood, however. To that end, we are conducting a series of developmental assays at various temperatures with different life stages to identify if a facultative diapause occurs during the life cycle of eastern larch beetle. Understanding the effects of temperature on the life cycle of D. simplex will be critical to understanding the effects of D. simplex on tamarack under a changing climate.