Long-term persistence of imidacloprid and olefin in eastern hemlock: Implications for hemlock woolly adelgid suppression in Great Smoky Mountains National Park

Hemlock woolly adelgid (HWA), Adelges tsugae (Annand), has devastated eastern hemlock populations in the eastern United States. Over the last ten years as the HWA front has progressed through Great Smoky Mountains National Park (GRSM), park personnel have applied systemic imidacloprid treatments to combat the threat to the Park’s hemlock resources. The effectiveness of imidacloprid treatments on HWA populations was examined four, five, and six years after application. Ten branchlet samples were taken from the canopies of hemlocks of four different size classes. Liquid chromatography-mass spectrometry was used to determine concentrations of imidacloprid and olefin, an imidacloprid metabolite that is ten times more toxic to insects than imidacloprid. Results indicate that olefin concentrations in foliage exceed lethal doses for HWA by over two-fold with imidacloprid present within foliage yet to be metabolized into olefin. HWA populations are still suppressed up to six years after a single imidacloprid treatment. Greater longevity of treatments will allow GRSM to extend time between treatments, facilitating a control program with effective HWA suppression and less pesticide application. This knowledge will enhance the HWA control program to protect and preserve eastern hemlock as an essential component of our forest systems in GRSM and the southern Appalachians.