Interspecific Variation in Ash Resistance to Emerald Ash Borer
Emerald ash borer (EAB) 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. To test the hypothesis in the case of ash resistance to EAB, a replicated common garden planting containing North American, European, and Asian ashes was established at the Michigan State University Tollgate Education Center in Novi, Michigan with the following objectives: (1) compare resistance of major North American, European, and Asian ash species to emerald ash borer, (2) identify mechanisms of resistance/susceptibility of ash species to EAB, and (3) determine the effects of drought and other stress on susceptibility of ash species to EAB, as well as North American ash borers. After two years, Manchurian ash (Fraxinus mandshurica), which shares an evolutionary history with EAB, had significantly fewer EAB exit holes and less EAB induced-dieback than did white (F. americana) and green ash (F. pennsylvanica) cultivars, as well as Northern Treasure ash (F. x ‘Northern Treasure’), which is a hybrid between native black ash (F. nigra) and Manchurian ash. These preliminary results are consistent with the hypothesis that Manchurian ash is a source of resistance genes to EAB by virtue of their coevolutionary history. However, it remains to be seen if this pattern will hold over time. Work is underway to determine whether this pattern has a phytochemical basis.
Herms, D. A.,
& Cipollini, D.
(2006). Interspecific Variation in Ash Resistance to Emerald Ash Borer. Emerald Ash Borer Research and Technology Development Meeting, 17.