Mechanisms of ash (Fraxinus spp) resistance to the emerald ash borer (EAB, Agrilus planipennis Fairmare)

Trees manifest two different types of defense against insects and pathogens: constitutive (pre-attack) and induced (post-attack). Constitutive defenses include the physical barrier represented by the outer bark and defensive proteins and secondary metabolites (mostly phenolics) toxic to the insect. Induced defenses include the formation of necrophylactic periderm and the induced accumulation of phenolics, lignin and defensive proteins.

Emerald ash borer [(EAB) Agrilus planipennis Fairmaire, Coleoptera: Buprestidae] was first discovered in Michigan in 2002. Since then it threatens to decimate all North American ash species (Fraxinus spp.). This has critical ecological and economic implications in urban and forest settings. Manchurian ash (Fraxinus mandschurica Ruprecht), an Asiatic species, has been shown to be resistant to the invasive insect pest emerald ash borer (EAB) (Agrilus planipennis Fairmaire, ). Such resistance, compared to the high susceptibility exhibited by North American ash species, has been hypothesized to be based on the co-evolutionary history shared by EAB and Asisan species of ash.

We work as part of a collaborative team to understand biochemical defense strategies in the ash trees. Consequently, we have taken a multipronged approach to dissect defense responses in ash trees by using cutting edge metabolomics (LC-MS/MS and LC-PDA) and proteomics (gel-based). These techniques are frequently used to identify and quantify constitutive and/or inducible levels of metabolites and/or proteins in tree phloem tissues.Additionally, we are also interested in understanding phytohormone induced defense mechanism.

Our final goal is to achieve a molecular level understanding of defense pathways in ash to improve management of this invasive pest through identification and generation of resistant ash cultivars and development of cultural and chemical management strategies to exploit natural plant defense responses.