Multiple year persistence of single treatments of imidacloprid to manage hemlock woolly adelgid on eastern hemlock: The benefits of metabolites

Hemlock woolly adelgid (HWA), Adelges tsugae (Annand), has devastated eastern hemlock populations in the eastern United States.  Since HWA was detected in the Great Smoky Mountains National Park (GRSM) in 2002, park personnel have applied systemic imidacloprid treatments to protect the Park’s hemlock resources.   The persistence of imidacloprid treatments on HWA populations was examined four to seven years after single applications. Branchlet samples were taken in three strata of the canopy from each of four size classes.  Liquid chromatography-mass spectrometry was used to assess concentrations of imidacloprid and its metabolite olefin, which is over ten times more toxic to insects than imidacloprid.  Imidacloprid and olefin both remain in the foliage four to seven years after treatment.  Imidacloprid still present within foliage will be metabolized into olefin for further control.  Greater longevity of treatments will allow GRSM to extend time between treatments, allowing effective suppression of HWA populations while reducing the frequency of pesticide applications to the environment.  Knowledge of the longevity of imidacloprid treatments is important for enhancing the HWA control program in GRSM.