Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Plants, Soils, and Insects

Major Professor

Paris Lambdin

Committee Members

Jerome F. Grant, Jennifer Franklin, Nicole Labbe


Extensive mortality of eastern hemlock, Tsuga canadensis (L.) Carrière, resulting from infestation by hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae) (HWA), has occurred throughout the eastern United States. Imidacloprid, a systemic insecticide, is used to control hemlock woolly adelgid. The metabolism of imidacloprid in eastern hemlock produces two metabolites of toxicological interest, olefin and 5-hydroxy. The objectives of this study were to 1.) determine the distribution and persistence of the metabolites in eastern hemlock in the southern Appalachians, 2.) their effect on hemlock woolly adelgid mortality, 3.) assess the tri-trophic movement of these compounds, 4.) evaluate the effects of hemlock woolly adelgid infestation levels on water stress, and 5.) assess the use of near-infrared spectroscopy for predicting imidacloprid concentrations in needle tissue.

Imidacloprid and 5-hydroxy concentrations in sap was highest at 12 months post-treatment and in twig and needle tissue was highest at 15 months post-treatment. Imidacloprid was detected through month 36 post-treatment and 5-hydroxy was detected through month 15 post-treatment. Olefin concentrations progressively increased in both sap and twig and needle tissue through month 36 post-treatment. Concentrations of imidacloprid were highest in the bottom stratum of the canopy and lowest in the top stratum. Concentrations of olefin and 5-hydroxy were highest in the top stratum and lowest in the bottom stratum. A significant relationship was found between imidacloprid concentrations > 158 ppb and olefin concentrations > 7 ppb and hemlock woolly adelgid mortality greater than 80% in field studies. In dose-response tests imidacloprid concentrations greater than 131 ppb and olefin concentration greater than 7 ppb were associated with high levels of hemlock woolly adelgid mortality (> 80%). Tri-trophic movement of imidacloprid and olefin was documented through 2 years post-treatment. The highest level of water stress was found in those trees with hemlock woolly adelgid infestation levels greater than 75%. The lowest level of water stress was found in those trees with less than 25% hemlock woolly adelgid infestation levels. Near-infrared spectroscopy results indicate that it can be used to predict concentrations of imidacloprid in needle tissue.

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