Variations in olefin concentrations among different size hemlock trees: Implications for management of hemlock woolly adelgid

Hemlock woolly adelgid (HWA), Adelges tsugae (Annand), has caused widespread eastern hemlock mortality in the eastern U.S.  HWA was first documented in the Great Smoky Mountains National Park (GRSM) in 2002, when GRSM personnel implemented an aggressive integrated pest management program to combat this invasive pest.  Systemic imidacloprid treatments have been applied by park personnel to preserve the park’s hemlock resources.  A retrospective study was conducted in cooperation with GRSM to examine the long-term effectiveness of imidacloprid treatments on different size hemlock trees.  Of particular interest is olefin, a metabolite of imidacloprid, which is greater than ten times more toxic to HWA than imidacloprid. Branchlets (0.5m) were collected from trees that received an imidacloprid basal drench treatment four to seven years before sampling.  Samples were collected from three strata of the canopy from each of four size classes.  Concentrations of imidacloprid and olefin (ppb) were determined by liquid chromatography-mass spectrometry.  HWA were counted on each branchet to assess populations.  A generalized linear model was used to analyze chemical data (p<0.05) and HWA data were analyzed with a zero inflated Poisson regression (p<0.05). Imidacloprid and olefin were present in all size classes four to seven years after an  imidacloprid treatment, and HWA populations were still suppressed (12.84 HWA/branchlet).  In general, larger hemlocks had higher concentrations of both imidacloprid and olefin.  Information obtained from this study can assist GRSM personnel in future development of their HWA suppression program to maintain low HWA populations while reducing the frequency of imidacloprid applications.