Pre-invasion assessment of exotic bark beetle-vectored fungi to detect tree-killing pathogens.

Exotic diseases and pests of trees have caused continental-scale disturbances in forest ecosystems and industries, and their invasions are considered largely unpredictable. We tested the concept of pre-invasion assessment of not-yet invasive organisms, which enables empirical risk assessment of potential invasion and impact. Our example assesses fungi associated with Old World bark and ambrosia beetles and their potential to impact North American trees. We selected 55 Asian and European scolytine beetle species using host-use, economic, and regulatory criteria. We isolated 111 of their most consistent fungal associates and tested their effect on four important Southeastern American pine and oak species. Our test dataset found no highly virulent pathogens that should be classified as an imminent threat. Twenty-two fungal species were minor pathogens, which may require context-dependent response for their vectors at North American borders, while most of the tested fungi displayed no significant impact. Our results are significant in three ways: they ease the concerns over multiple overseas pests suspected of heightened potential risk; they provide basis for focus on the prevention of introduction and establishment of species that may be of consequence; and they demonstrate that pre-invasion assessment, if scaled up, can support practical risk assessment of exotic pathogens.