Naturally-occurring adelgid resistance in eastern hemlocks
My work surveying hemlock forests led me to become interested in whether rare eastern hemlock individuals might possess some degree of innate resistance to the hemlock woolly adelgid A. tsugae. I helped develop a citizens’ science program that involved environmental groups throughout the east coast in the search for healthy hemlock trees growing in adelgid-devastated forests. This initiative turned up a number of potentially resistant trees, growing both individually or in small stands; my collaborators and I took cuttings from the most promising individuals and treated them to induce rooting in order to experimentally assess their adelgid resistance in a controlled environment. We have a number of promising candidate trees in cultivation, and four years of testing both grafted and clonally-propagated accessions derived from ‘putatively resistant’ individuals has shown a clear pattern: lower adelgid settlement and increased adelgid mortality relative to cuttings from control trees.
For a great description of the effects of hemlock woolly adelgid, take a look at “A Death in the Forest,” written by Richard Preston for The New Yorker.