Beauty and the beast: mechanisms of host-plant resistance to hemlock woolly adelgid (Adelges tsugae)

The invasive hemlock woolly adelgid (Adelges tsugae) causes extensive mortality of two hemlock trees in eastern North America (eastern hemlock, Carolina hemlock). Variation in resistance between and within hemlock species are recognized, but mechanisms of resistance are unknown. Investigations into host chemistry and physical characteristics reveal possible explanations for this variation. Analyses of foliar waxes may indicate compositional differences between resistant and susceptible hemlocks. Trichomes on the hemlock do not play a role in resistance, but cuticle thickness at the feeding site may. Perception of their host by the adelgid may have implications for cues used to select their feeding site. Sensillae are studied with scanning electron microscopy and function hypothesized based on morphology. This research will improve selection and screening processes for resistant hemlock breeding programs.