Progress and gaps in understanding mechanisms of ash tree resistance to emerald ash borer, a model for wood-boring insects that kill angiosperms.
We review the literature on host resistance of ash to emerald ash borer (EAB, Agrilus planipennis), an invasive species that causes widespread mortality of ash. Manchurian ash (Fraxinus mandshurica), which coevolved with EAB, is more resistant than evolutionarily naïve North American and European congeners. Manchurian ash was less preferred for adult feeding and oviposition than susceptible hosts, more resistant to larval feeding, had higher constitutive concentrations of bark lignans, coumarins, proline, tyramine and defensive proteins, and was characterized by faster oxidation of phenolics. Consistent with EAB being a secondary colonizer of coevolved hosts, drought stress decreased the resistance of Manchurian ash, but had no effect on constitutive bark phenolics, suggesting that they do not contribute to increased susceptibility in response to drought stress. The induced resistance of North American species to EAB in response to the exogenous application of methyl jasmonate was associated with increased bark concentrations of verbascoside, lignin and/or trypsin inhibitors, which decreased larval survival and/or growth in bioassays. This finding suggests that these inherently susceptible species possess latent defenses that are not induced naturally by larval colonization, perhaps because they fail to recognize larval cues or respond quickly enough. Finally, we propose future research directions that would address some critical knowledge gaps.
Department of Plant Pathology, The Ohio State University, Columbus, OH, 43210, USA.
Caterina
C
Villari
Department of Entomology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, OH, 44691, USA.
Daniel A
DA
Herms
Michael Smith Laboratories, The University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
Justin G A
JG
Whitehill
Department of Biological Sciences, Wright State University, Dayton, OH, 45435, USA.
Don
D
Cipollini
Department of Plant Pathology, The Ohio State University, Columbus, OH, 43210, USA.
Pierluigi
P
Bonello
D000085:Acetates / Q000494:pharmacology; D000818:Animals; D000890:Anti-Infective Agents / Q000378:metabolism; D000898:Antibiosis; D001517:Coleoptera / Q000502:physiology*; D003517:Cyclopentanes / Q000494:pharmacology; D031661:Fraxinus / Q000276:immunology* / Q000469:parasitology; D005960:Glucosides / Q000378:metabolism; D007814:Larva; D008031:Lignin / Q000378:metabolism; D019684:Magnoliopsida / Q000276:immunology* / Q000469:parasitology; D008954:Models, Biological; D010058:Oviposition; D054883:Oxylipins / Q000494:pharmacology; D010636:Phenols / Q000378:metabolism; D010937:Plant Growth Regulators / Q000494:pharmacology*; D013045:Species Specificity; D014361:Trypsin Inhibitors / Q000378:metabolism; D014934:Wood; D059808:Polyphenols
D000085:Acetates; D000890:Anti-Infective Agents; D003517:Cyclopentanes; D005960:Glucosides; D008031:Lignin; D054883:Oxylipins; D010636:Phenols; D010937:Plant Growth Regulators; D014361:Trypsin Inhibitors; C058956:acteoside; D059808:Polyphenols; C072239:methyl jasmonate
Agrilus planipennis; Fraxinus; constitutive defense; emerald ash borer; host defense mechanisms; induced defense; plant-insect interactions; wood-borers