D3068: Improved characterization of the Ips paraconfusus Lanier (Coleoptera: Curculionidae) outbreak in Washington: Determining the role of drought and host resin defense

California five-spined ips, Ips paraconfusus Lanier (Coleoptera: Curculionidae), is an engraver beetle native to California and Oregon, where it parasitizes a variety of host pine species by boring holes into the cambium and consuming phloem tissue. In 2010, mortality of both small and large diameter ponderosa pine was recorded in the Columbia Gorge of Washington, and by 2023, mortality of ponderosa pine, as well as novel hosts Scots pine and Austrian pine, were recorded in the south Puget Sound. Tree resin acts as both a physical and chemical barrier to bark beetles, by physically encapsulating and pushing out beetles and containing oleoresins with toxic terpenoid compounds. To better characterize these outbreaks and determine the roles of drought and tree resin defenses, we collected increment cores from live/unattacked (L/U) and dead/attacked (D/A) trees across the south Puget Sound. From these cores, we compared the within-tree growth ratios of L/U and D/A trees against climate data as well as resin duct metrics, such as resin duct number and size. Preliminary results show that, on average, D/A trees experienced a decline in growth rate following a drought period from 2015 to 2019, whereas L/U trees experienced a recovered growth rate. Preliminarily, resin duct number and size also differed among L/U and D/A trees, with D/A trees, on average, having fewer and smaller resin ducts. This suggests that drought-stressed trees are more susceptible to attack by I. paraconfusus as they are unable to produce sufficient resin ducts through growth to protect them from attack.