Larval development and parasitism of emerald ash borer (Agrilus planipennis) in Oregon ash (Fraxinus latifolia) and European olive (Olea europaea): implications for the West Coast invasion.

Abstract

The invasive emerald ash borer (Agrilus planipennis Fairmaire) (EAB) has been devastating North American ash (Fraxinus spp.) resources for over 2 decades. In its native range, EAB attacks and kills primarily stressed ash trees. In North America, however, EAB also attacks healthy trees of every Fraxinus species encountered, most recently Oregon ash (Fraxinus latifolia Benth.). Successful EAB development has also been reported in European olive (Olea europaea L.). The recent detection of EAB in Oregon puts the future of these 2 hosts into question, as little is known about EAB's development in these species or how introduced biocontrol agents will respond. We conducted laboratory and field infestations of olive and ash in Delaware and Oregon to assess EAB development and associated parasitoid responses. We found no difference in the net population growth rate of EAB developing in Oregon ash versus green ash. However, these species supported significantly more population growth than olive, in which EAB net population growth rate was zero, with most larvae dying prematurely. Artificially infested olives were small, which may have negatively impacted phloem availability and larval survival. Future studies should be conducted investigating EAB development on larger olive material. Although no parasitism was observed in infested olive, as EAB larvae seldom reached life stages (third or fourth instars) susceptible to larval parasitism, late-instar larvae developing in Oregon ash were attacked by both Tetrastichus planipennisi Yang and Spathius galinae Belokobylskij and Strazanac, suggesting that biocontrol is a suitable option for this newly invaded region.