Towards developing ash varieties resistant to emerald ash borer and increasing the efficacy of its biological control agents

The emerald ash borer (EAB; Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae) is a phloem-feeding exotic wood borer introduced from Asia that is spreading throughout the Midwest with devastating effect. This beetle is capable of killing otherwise healthy trees and colonizes trees as small as saplings – most affected trees die within four years of colonization. Asian ash species (i.e., Manchurian and Chinese) appear to be more resistant to EAB than those native to North America (e.g., green, white, and black ash). In this project we use reciprocal grafts of these five ash species to determine whether resistance to EAB can be conferred to a scion when grafted onto resistant rootstock. Specifically, we collected head-space volatiles from twigs and leaves of the grafted ash trees to determine the extent to which: 1) rootstocks influence the composition of volatile organic compounds (VOCs) released by the scion; and 2) herbivory by adult female beetles induces changes in the VOCs released by the reciprocal grafts. In addition to this, we harvested phloem tissue samples from the trees and performed constitutive phenolic analysis. This work may pave the way toward developing systems for propagating Fraxinus scions that are resistant to EAB and exploit potential phytochemical connectivity between roots and shoots.