Emerald ash borer (EAB, Agrilus planipennis) is an invasive Asian wood borer considered an ash tree (Fraxinus spp.) specialist, but capable of detecting and utilizing white fringetree (WF, Chionanthus virginicus) and cultivated olive (OL, Olea europaea). Use of these novel hosts appears to be due to ecological fitting. The performance of larvae on these two non-ash hosts is lower than susceptible North American ash. On the ancestral host, Manchurian ash, and North American hosts, EAB performs better when the plant is stressed. Conversely, host plants that are better defended from EAB with an induction treatment of methyl jasmonate (MeJA) has shown a to reduce beetle numbers in hosts. We conducted three experiments to determine the susceptible of non-ash hosts to EAB from three stressors: previously attacked hosts (WF), girdled hosts (WF and OL), and methyl jasmonate (WF) treated hosts compared to control stems. Olive and white fringetree plants were infested with EAB eggs in late spring and larvae fed over the course of a summer. By the end of the field season, infested stems were debarked to assess larval survivorship and performance.
Results/Conclusions
Larvae in control WF developed shorter galleries and died in contrast to previously attacked trees and girdled trees, stressed plants. Survivorship was observed to be very low in stressed WF suggesting that EAB does not perform well in this non-ash host. WF treated with MeJA had two larvae survive (<8%) and only occurred on one stem. In olive trees, no larvae survived in either treatment, although more galleries created in girdled, stress plants. The morality was surprising because EAB have survived in cut stems of olive and a live potted plant previously. These results suggest for olive that young/small diameter stems may be able to resist EAB while larger stems may be more susceptible possibly due to photoactivity in small stems. The white fringetree results demonstrate that like Manchurian ash, this host becomes more susceptible to EAB when stressed, but the treatment of MeJA needs to be further investigated.