Emerald ash borer is an aggressive killer of even healthy ash in North America. However, reports suggest that EAB does not devastate ash in Asia, but rather that isolated outbreaks occur in response to stresses such as drought. Thus, emerald ash borer seems to behave in Asia much as its close native buprestid relatives do in North America, colonizing only stressed trees. This implies that Asian ashes may be generally resistant, with weakened trees preferentially colonized. Native trees may be more resistant to native pests because of natural defenses that have developed over their long coevolutionary history. This hypothesis is supported by a 20-year study of birch resistance to bronze birch borer conducted in Ohio where birches native to North America were found to be highly resistant to bronze birch borer, while European and Asian species were extremely susceptible. To test the hypothesis in the case of ash resistance to EAB, a replicated common garden planting containing native, European, and Asian ashes was established in Novi, Michigan with the following OBJECTIVES: (1) compare resistance of major North American, European, and Asian ash species to emerald ash borer, and (2) identify mechanisms of resistance / susceptibility of ash species to EAB. After one year, Manchurian ash (F. mandshurica), which shares an evolutionary history with EAB, had significantly fewer EAB exit holes and minimal EAB induced-dieback, relative to white (Fraxinus americana) and green ash (F. pennsylvanica) cultivars. These results are consistent with the hypothesis that Manchurian ash is a source of resistance genes to EAB by virtue of their coevolutionary history. Work is underway to determine whether this pattern has a phytochemical basis.