Host Preference, Nutrition, and Defense

Research Issue

The emerald ash borer (EAB) has killed hundreds of millions of ash trees in North America since its discovery in 2002.  All eastern North American ash species are susceptible to EAB including green, white, black, blue, and pumpkin ash.  Asian ash species in EAB’s native range appear to have some level of resistance.  Susceptibility and preference vary among North American ash species, with green ash being highly preferred and susceptible and blue ash much less preferred and susceptible.  Many factors may contribute to host preference and suitability including physical qualities of the host (e.g., bark roughness, leaf texture), host volatiles, nutritional quality of the host, and the presence and abundance of defensive mechanisms and compounds.

Our Research

We conducted EAB feeding choice experiments with leaves from different ash species presented to EAB in cages in order to determine EAB preference for different species of ash.  We collected and analyzed volatiles from ash trees of different species and compared their volatile profiles related to EAB feeding preference.  Leaves and phloem were sampled and extracted for chemical analysis to elucidate differences in nutritional and defense chemistry of different ash species and examined their roles in EAB preference and performance. 

Expected Outcomes

Understanding host preferences by EAB is important in prioritizing survey and management of different ash species.  Discerning the mechanisms of host preference and resistance will be critical for incorporation into ash breeding programs to develop resistant trees.

Research Results

Although beetles consumed every ash species offered to them, Manchurian ash and blue ash were significantly less preferred than green ash, white ash and black ash while European ash was intermediate.  The overall volatile profiles of different ash species differed significantly in their relative amounts of antennally active compounds. Moisture content and nutrients were important selective forces in feeding behavior of EAB larvae.  Improved nutrient balance (total nitrogen/total non-structural carbohydrate ratio) and increased efficiency of amino acid utilization in green ash may contribute to its preference by EAB.  Elevated levels of volatile compounds induced by adult foliar feeding in green and white ash, and lower levels of induced defensive compounds including phenolics and protease inhibitors in green ash, may also partially explain the preference for green ash by EAB.  Negative effects of defense compounds might be alleviated by high nitrogen levels and by direct excretion or enzymatic conversion of defense compounds.

Poland, T. M.; Chen, Y.; Koch, J.; Pureswaran, D.  2015.  Review of the emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae), life history, mating behaviours, host plant selection, and host resistance.  The Canadian Entomologist. 147: 252–262.

Chen, Y.; Ulyshen, M.D.; Poland, T.M.  2012.  Differential Utilization of Ash Phloem by Emerald Ash Borer Larvae: Ash Species and Larval Stage Effects.  Agricultural and Forest Entomology 14: 324-330.

Chen, Y.; Ciaramitaro, T.; Poland, T.M.  2011.  Moisture Content and Nutrition as Selection Forces for Emerald Ash Borer Larval Feeding Behavior.  Ecological Entomology 36: 344-354.

Chen, Y.; Whitehill, J.G.A.; Bonello, P.; Poland, T.M.  2011. Differential response in foliar chemistry of three ash Species to Emerald Ash Borer Adult Feeding.  Journal of Chemical Ecology  37: 29-39.

Chen, Y.; Poland, T.M.  2010. Nutritional and defensive chemistry of three North American ash species: possible roles in performance by emerald ash borer adults.  The Great Lakes Entomologist.  43: 20-33.

Chen, Y.; Whitehill, J.G.A.; Bonello, P.; Poland, T.M.  2010.  Feeding by Emerald Ash Borer Larvae Induces Systemic Changes in Black Ash Foliar Chemistry.  Phytochemistry 72: 1990-1998.

Pureswaran, D.S.; Poland, T.M.  2009.  Host selection and feeding preference of the emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) on ash (Fraxinus spp.).  Environmental  Entomology 38:757-765.

Research Participants

Principal Investigators

• Yigen Chen, University of California at Davis (formerly at Michigan State University)
• Therese Poland, US Forest Service - Northern Research Station Research Entomologist
• Deepa Pureswaran, Natural Resources Canada Research Scientist
• Tina Ciaramitaro, US Forest Service - Northern Research Station Biol. Lab. Tech.

Research Parthers

• Enrico Bonello, Ohio State University
• Justin Whitehill, Ohio State University