Research Highlights

Summary

North American green ash is highly susceptible to emerald ash borer. Improved nutrient balance and efficiency of amino acid utilization in green ash, together with reduced induction of defense compounds, may contribute to the green ash preference by emerald ash borer. Understanding the differences in nutritional and defensive chemistry among ash species and their roles in emerald ash borer preference and performance will help to elucidate mechanisms of host preference and resistance and thus aid in resistant tree breeding programs.

The invasive emerald ash borer was first discovered near Detroit, MI, in 2002. It has since spread to 16 States and two Canadian provinces and has killed an estimated 50 to 100 million ash trees, causing devastating economic and ecological effects. All Eastern North American ash species are susceptible to the beetle to some degree, including green, white, black, blue, and pumpkin ash, with green ash being highly preferred and susceptible. Asian ash species in the beetle's native range appear to have some level of resistance.

A Forest Service scientist is working with colleagues to elucidate differences in nutritional and defense chemistry of different ash species and examine their roles in emerald ash borer's preference and performance. Understanding the mechanisms of host preference and resistance will be critical for ash breeding programs to develop resistant trees.

Research suggested that moisture content and nutrients were important selective forces in feeding behavior of the beetle's larvae. Improved nutrient balance and increased efficiency of amino acid utilization in green ash may contribute to its preference by emerald ash borer. Elevated levels of volatile compounds induced by adult foliar feeding in green and white ash, and lower levels of induced defensive compounds in green ash may also partially explain the preference for green ash by emerald ash borer.

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