The resin defenses of eastern larch in response to eastern larch beetle: exploring insect-host dynamics under changing climatic conditions.

Abstract

Dendroctonus bark beetles and conifers have coexisted in a dynamic equilibrium for millions of years. Although at times disrupting human goals for economic products, disturbances wrought by bark beetles are a critical component of forest successional dynamics. More recent anthropogenic impacts including climate change and the creation of vulnerable landscapes have increased the incidence and severity of bark beetle related tree mortality in North America beyond standard ecological parameters. One such example is an unprecedented outbreak of the native eastern larch beetle (ELB), Dendroctonus simplex LeConte (Coleoptera: Curculionidae; Scolytinae), in the eastern larch (tamarack), Larix laricina (Du Roi) K. Koch, forests of Minnesota. Warmer temperatures and extended growing seasons likely contributed to rapidly building numbers of ELB, resulting in a more aggressive population that attacks vigorous, large diameter trees. ELB have killed tamarack across 400,000 ha of forest in the state since 2001. An important driver of beetle-host interactions is tree defenses, especially resin, but little is known about these systems in tamarack. This work explores the defensive capacity of tamarack with a dendrochronological analysis of resin conducting networks visible in tree cores collected as part of foundational ELB research in 2011-2013, and an observational study of resin output repeated over the course of the growing season of 2023. Both studies illuminate a mismatch between the evolved defensive strategy of trees and current beetle population dynamics and address the limitations of current forest research and management models in a rapidly changing world.