D3065: Does the number of resin ducts predict survival of tamarack (Larix laricina) from outbreaks of eastern larch beetle (Dendroctonus simplex)?

The eastern larch beetle, Dendroctonus simplex, (Coleoptera: Scolytinae) is native to North America and is found throughout the range of its primary host, eastern larch or tamarack (Larix laricina). Previously considered “nonaggressive,” eastern larch beetles commonly target trees stressed by age, injury, or environmental factors. Historically, even during eruptions of eastern larch beetle populations, tamarack mortality occurred in isolated pockets without widespread landscape-level impacts. However, recent outbreaks have had more devastating effects on large tracts of tamarack, including otherwise healthy trees. One such outbreak began in 2001 in northern Minnesota and has impacted approximately half the tamarack forest cover in the state. This massive mortality event presents an interesting case study for understanding the factors contributing to this more aggressive beetle behavior as it occurred in areas not otherwise predisposed for large-scale attack. Little is known about the defensive responses of tamarack trees to beetle colonization. Our team collected phloem samples from living tamarack located near beetle outbreak epicenters and monitored for subsequent colonization over the course of three summers.  This study explores whether resin duct numbers in these phloem samples were correlated with tree survival as the beetle outbreak moved across the landscape. Understanding the capacity of individual trees to fend off these more aggressive attacks has implications for management practices in response to these increasingly more common eruptions of eastern larch beetle.