Pine wars: Mass attack dynamics of mountain pine beetle (Dendroctonus ponderosae Hopkins) in novel host jack pine

Climate change can be observed globally through range expansion of insects. Mountain pine beetle (MPB) Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), has expanded its historically Western North American range into Northern and Central Alberta, Canada where it has attacked the novel host, jack pine. Using pheromone-mediated mass attack during the epidemic population state, MPB are capable of overwhelming vigorously defended trees (≈40 beetles/square metre). Past this mass attack threshold, brood success increases until the optimal attack density is reached (≈60 beetles/square metre). Above the optimal attack density, brood success declines with competition for finite resources under the bark. Our current understanding of MPB mass attack dynamics originates from studies performed in the historic host, lodgepole pine. Jack pines have different chemical defence profiles and are not adapted to MPB attack compared to lodgepole pines. To quantify mass attack dynamics in jack pine, we manipulated attack densities in jack pines in the field. We mass reared and released MPB under caged tree boles. After the attack period, we harvested manipulated trees and brought bolts to the lab and measured gallery characteristics and the number of offspring produced. The mass attack threshold and optimal attack densities are lower in jack pine compared to lodgepole pine. Gallery characteristics differ greatly in jack pine compared to lodgepole pine. Understanding how mass attack dynamics are different in jack pine will allow us to predict the long-term population dynamics of MPB in its expanded range and potential for spread through Canada’s boreal forest.