The Chemical Ecology and Insect Associates of the Eastern Larch Beetle (Dendroctonus simplex LeConte)

Abstract

The eastern larch beetle, Dendroctonus simplex LeConte (Coleoptera: Curculionidae: Scolytinae), is a native insect ranging from Alaska through the western provinces of Canada, dipping down into the Great Lakes region, and extending to the northeast United States and Canadian maritime regions. Historically, this beetle exhibited outbreaks of three to five year durations in stands of tamarack, Larix laricina (Du Roi) K. Koch, predisposed to attack after experiencing stress such as defoliation, drought, wind throw, fire, or flooding. Recently, 20+ year outbreaks have been observed in portions of the southern transcontinental range of the insect, likely exacerbated by growing seasons that permit more than one generation of eastern larch beetle per year. In Minnesota, an outbreak has affected more than 75% of tamarack covertype in the state since 2001. I worked to expand our knowledge of the beetle’s chemical ecology and natural enemy complex. Specifically, I characterized monoterpenes in the phloem of regional host trees, isolated pheromones produced by D. simplex, and assessed antennal responses of these beetles to these compounds. I observed beetle walking and flight responses to beetle and host compounds and documented insect biodiversity within the regional tamarack ecosystem. I discovered that ⍺-pinene and ∆-3-carene were the most prominent compounds present in tamarack phloem. I found that unmated female beetles produce seudenol and low quantities of frontalin to which male beetles respond. After mating, female beetles cease to produce seudenol, instead increasing frontalin production. At high dosages (at or over 3 mg/day release rates), male and female beetles show repulsive responses to frontalin. The attraction of natural enemies such as Thanasimus spp. is positively correlated with frontalin concentration. My work suggests that high-dosage frontalin could be explored as a repellent for high-value trees and as an option for eastern larch beetle management. Finally, my biodiversity survey chronicled 185 unique taxa captured in Lindgren funnel traps. Biodiversity indices such as Shannon diversity, species evenness, species richness, and abundance shifted throughout each summer with Shannon diversity and species evenness reaching the lowest level in mid-June and species richness and abundance peaking at these same dates.