A small proportion of non-native insects cause widespread ecological and economic damage on a global scale, but the ability to predict their level of damage has eluded scientists for decades. Advancements in the study of invasion biology and fields such as computational phylogenetics provides tools that could help to quantify the drivers that influence the eventual impact of a non-native insect. Understanding these drivers informs management decisions including risk assessments for insects not yet established in North America but have a high likelihood of introduction given global trade pathways. Our working group, sponsored by the US Geological Survey’s John Wesley Powell Center for Analysis and Synthesis, is using established literature and databases to quantify the contribution of multiple invasion components: 1) insect traits (e.g. feeding guild, voltinism, fecundity), 2) phylogenetic distance between the insect’s native and North American host plants, 3) host plant traits (e.g. C:N ratio, shade tolerance, specific leaf area), and 4) evolutionary history between the non-native insect and its closest relative native to North America that shares the same host.
Results/Conclusions
As a proof-of-concept, we focused on the non-native insects considered to be conifer specialists – those that feed only on species of Pinaceae, Cupressaceae, and/or Taxaceae; approximately 60 insects met our criteria. We then developed an impact score for each insect, in which a rank of 1 indicated there were no references of damage in the literature, while a rank of 9 indicated that the insect has or will likely cause functional extinction of the host plant. Our results reveal that a number of factors may contribute to an insect’s impact, suggesting a framework involving multiple components would be optimal for prediction. For example, we found a greater probability of the insect being high impact if congener species native to North America were absent (possible lack of top-down effects), its host had a slow growth rate (possible lack of bottom-up effects), the insect’s native and North American hosts diverged from their most recent common ancestor 12.5-15 million years ago, and there were no closely related insects (e.g. within the same suborder) with which the North American host had coevolved. Our future work will extend this framework to specialist herbivores of Angiosperm trees, and potentially all non-native herbivorous insects in North America.