Susceptibility and suitability of northeastern North American pines for mountain pine beetle, Dendroctonus ponderosae Hopkins

Abstract

The mountain pine beetle (Dendroctonus ponderosae Hopkins) is the most aggressive bark beetle (Coleoptera: Curculionidae) in western North America. This insect is currently expanding its range eastward through the Canadian boreal forest. Continued range expansion, or introduction via infested material from western North America, could lead to novel associations between the mountain pine beetle and eastern pines. This research seeks to determine the susceptibility and suitability of pine species common to northeastern North America for mountain pine beetle. Studies were conducted in a common garden environment on logs of four common eastern pines, red (Pinus resinosa), jack (P. banksiana), eastern white (P. strobus) and Scots (P. sylvestris) pine, and two historic hosts, lodgepole (P. contorta) and ponderosa (P. ponderosa) pine. Constitutive defenses pose no significant barrier to colonization of eastern pines by mountain pine beetle. The proportion of female beetles that established fertile egg galleries differed among eastern pines, but were similar to historic hosts. Foraging beetles were generally no more attracted to logs of eastern pines containing boring beetles than to a control. Chemical analysis of the phloem suggests that host kairomones critical for secondary attraction were minimal among novel pines and likely resulting in less attraction than to historic hosts. Overwintering capacity of developing brood was affected by eastern pines. Rapid development in novel pines resulted in greater proportions of brood entering winter in less cold tolerant life stages than historic hosts. The strategy and degree of cold tolerance of fourth instars were affected by natal pine host. Field validation of logistic regression models demonstrated that models based on the insect freezing temperature underestimate cold mortality, while lower lethal temperature curves more accurately project mortality due to cold. Finally, we found that constitutive defenses pose no barrier to reproduction among novel pines. Indeed, novel pines can have up to twice the reproductive potential, and demonstrate greater brood fitness than historic hosts. However, variable rates of development among novel hosts could result in desynchronized or extended emergence periods in mixed stands. Matches between species specific development rates and climate will be crucial for outbreaks to occur in eastern forests.