The value of hybrid and non-native ash for the conservation of ash specialists is limited following late stages of emerald ash borer invasion

Widespread mortality of native North American ash caused by emerald ash borer (EAB; Agrilus planipennis Fairmaire) threatens native arthropod biodiversity, but hybrid ash populations with resistance to EAB may serve a role in supporting threatened communities of arthropods in managed landscapes impacted by EAB. In this study, we investigated the hypothesis that a North American x Asian hybrid ash could serve as a refuge for North American arthropods in a common garden experiment by comparing beetle communities and herbivory on North American green and black ash, the Asian Manchurian ash, and the black x Manchurian hybrid 'Northern Treasure' ash. We found that ash specialists were rare among trees in the common garden. Species richness and composition of herbivorous beetles, as well as levels of herbivory, were similar among ash taxa, and these patterns were driven by native generalists. The lack of ash specialists collected suggests that regions that have experienced late stages of EAB-induced ash mortality may have missed the opportunity to conserve populations of native specialist herbivores with EAB-resistant ash genotypes. To maximize the potential for conserving native arthropod biodiversity of ash, it may be necessary to plant resistant ash prior to widespread EAB-induced ash mortality, prioritizing efforts on the leading edge of expanding distribution of EAB.

Automated summary

The study suggests that hybrid ash populations with resistance to emerald ash borer may play a role in supporting threatened arthropod communities in managed landscapes. However, ash specialists were rare in the common garden experiment, with herbivorous beetle richness, composition, and levels of herbivory being driven by native generalists. The findings highlight the importance of planting resistant ash species prior to widespread ash mortality caused by emerald ash borer to conserve native arthropod biodiversity.