Emerald ash borer host range expansion: Implications for the invasion in Oregon

The invasive emerald ash borer (Agrilus planipennis Fairmaire) (EAB) has been wreaking havoc on North American ash resources for over two decades. In its native range, EAB is a secondary pest, attacking and killing primarily stressed trees. In North America, EAB’s host range has expanded to include healthy trees of every Fraxinus species encountered, most recently Oregon ash (Fraxinus latifolia Benth.). Successful EAB development has also been reported on European olive (Olea europaea L.), an important economic crop in the western United States. EAB’s recently confirmed presence in Oregon puts the future of these novel hosts into question, as little is known about EAB’s developmental success on these species, especially in this newly invaded region. Furthermore, it is unknown how biocontrol agents will respond to EAB developing in these new hosts. In spring 2023, we artificially infested Oregon ash, green ash (Fraxinus pennsylvanica Marsh.), and European olive trees in Forest Grove, OR with EAB. The following fall and spring, we debarked these trees, recorded larval fates and developmental stages, and conducted life table analysis to determine EAB net population growth rate (λ) on each species. We found no difference in λ of EAB developing on Oregon ash versus green ash, but these species supported significantly more population growth than olive, on which λ was 0, with most larvae dying in early instars. Furthermore, we found evidence of larval parasitism on Oregon ash, suggesting that biocontrol is a suitable option for this region.