This presentation illustrates some of our findings on existing host resistance to hemlock woolly adelgid in native hemlock stands and exotic hemlocks. The author, Kelly Oten, graduate research and teaching assistant, won third place for the presentation at the student competition during the Southeastern Branch Entomological Society of America meeting this year.

HWA resistance PDF for ASTF website (PDF file – This will open the presentation in a new window, so you can read the presentation and look at the comments to see what each slide is about)

Comments for slides:

Slide 5: Since the hemlock woolly adelgid (HWA) is wingless, it must be transported passively, on the bodies of birds and/or deer or via the wind.  Therefore, the adelgid’s ability to location its habitat and host are not in its control.  We are interested in the acceptance of the feeding site, in this case the base of the hemlock needle, of HWA.  The next slides will detail out investigations into how the feeding site is selected by HWA.

Slide 6: We are interested in understanding host acceptance because it has implications for host plant resistance.  Know the characteristics to look for in resistance trees will make for rapid identification of resistant trees in naturally occurring stands as well as screening for resistance in breeding programs.

Slide 7: Trichomes are sometimes used as defense to herbivores; these images show eastern hemlock (T. canadensis) covered in trichomes, indicating that trichomes do not deter HWA feeding.

Slide 8: We investigated the thickness of the layer HWA must penetrate to feed.  This is currently inconclusive; our future plans are to inspect Chinese hemlock.

Slide 11: The next three slides show sensillae that will be looked at under higher magnification.  Investigating the morphology of sensillae may give us a clue as to their function.

Slide 15: Please view the video posted below. This shows the selection of the feeding site by HWA.

HWA settling (2m 26s) (WMV file) Watch a hemlock woolly adelgid scurry around on a hemlock branch before finding an appropriate feeding site.