Influence of temperature on development of eastern larch beetle Dendroctonus simplex LeConte and reproductive success in two novel Larix hosts

Abstract

Eastern larch beetle, Dendroctonus simplex LeConte (Coleoptera: Curculionidae: Scolytinae), is a bark beetle native to North America that feeds and reproduces in the phloem of its host, the eastern larch (tamarack) Larix laricina (Du Roi) K. Koch. As of 2024, approximately 75% of eastern larch forest type in Minnesota has been impacted by an ongoing eastern larch beetle outbreak that began in 2001. Climate is proposed as a major factor for the outbreak as longer and warmer growing seasons result in higher beetle populations. My thesis research evaluates how temperature affects each stage of eastern larch beetle development and tests the reproductive success of the beetle in two potential novel hosts, western larch (Larix occidentalis Nutt.) and subalpine larch (Larix lyalli Parl). In the first chapter, I used phloem sandwich assays to observe development of each life stage of eastern larch beetle at six temperatures ranging from 8°C-27.9°C. A developmental delay indicative of a facultative, pre-pupal diapause was identified within third and fourth instar larvae when exposed to temperatures below 14°C and 17°C, respectively. In the second chapter, I compared the reproductive success of eastern larch beetle in cut bolts of western larch and subalpine larch to its native host, eastern larch, in a host suitability study. I observed that the eastern larch beetle is capable of reproduction in all three hosts, and that the beetle performed similarly in eastern and subalpine larch. As global change facilitates introduction and range expansion of insect pests, these findings indicate that eastern larch beetle may pose a future threat to subalpine larch, should range expansion occur.