Research by Northern Research Station scientists and their partners presents the first evidence supporting a long-held hypothesis that a tree’s evolutionary history is key to its susceptibility to nonnative herbivorous insects. This discovery has the potential to be a game-changer in predicting the impact of and managing nonnative insects.

For more than a century, scientists have worked with little success to understand why some nonnative insects prove devastating and others harmless. In a study of invasive insects affecting conifer species, a research team that includes scientists from the USDA Forest Service, the U.S. Geological Survey, industry, and universities has turned the problem around by considering the insects’ host tree species and how they have evolved rather than focusing solely on the insect. The result is a novel model for assessing the probability that nonnative insects that have not yet arrived in North America will cause widespread mortality of North American conifer species. The study revealed that when host trees in an insect’s native range are very closely related or very distantly related to its host trees in the invaded range, there is a low probability of impact. However, when the relatedness of hosts in the native and introduced ranges are intermediate, there is a much higher probability of tree damage and death at the ecosystem scale. Advancing managers’ ability to predict which native trees are most susceptible to which nonnative insects has the potential to be a game-changer in managing risk from invasive species. Scientists are expanding the study to include species such as emerald ash borer that specialize on hardwood trees and generalists feeding on both conifers and hardwoods, such as the gypsy moth.