Dissecting the problem: Could differences in Fraxinus spp. anatomical characteristics influence host preference of emerald ash borer?

Emerald ash borer (EAB) (Agrilus planipennis, Fairmaire) was first identified near Detroit, Michigan in 2002 after arriving from Asia on solid wood packaging material. In its native range, EAB is considered a secondary pest, typically attacking only declining or stressed trees. North American Fraxinus trees are not colonized by native Agrilus beetles and lack an evolutionary history with EAB. This apparent lack of evolved resistance likely accounts for the tens of millions of ash trees that have been killed to date in Michigan. In North America, EAB host preference or the ability of trees to resist EAB varies among ash species. Previous studies have shown F. pennsylvanica is usually colonized at higher densities than F. americana when they co-occur while larval density is often higher on F. americana than on F. quadrangulata.

Because the mechanisms affecting variation in Fraxinus resistance to EAB is as yet unknown, we believe that information about the tree’s anatomical architecture is of value. For example, sap flow and lignification of colonized phloem could alter or prevent larval development. Bark thickness and structure could affect larval development or female oviposition preference. Sclerophylly and trichome density could affect digestibility of leaf tissues. We employed Confocal Laser Scanning Microscopy, to reconstruct three-dimensional images of stem and leaf samples taken from five Fraxinus species to compare anatomical characteristics. Preliminary results show that selected traits consistently vary among species. Effects of these traits on adult EAB host preference and larval development are underway.