Distribution of trunk-injected 14C-imidacloprid in ash trees and effects on emerald ash borer (Coleoptera: Buprestidae) adults

The emerald ash borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae) is a destructive exotic pest of North American ash (Fraxinus sp.) trees. Trunk injection of imidacloprid is commonly used to protect landscape ash trees from A. planipennis damage. Efficacy can vary and little is known about the distribution, accumulation and persistence of this compound in trees. Green ash (Fraxinus pennsylvanica) and white ash (Fraxinus americana) trees were injected with 25 μCi of 14C-imidacloprid plus non-labeled imidacloprid and were grown under water-sufficient and water stress conditions. Tree trunks, twigs, leaves and roots were sampled periodically for two years following injection. Imidacloprid concentrations did not vary (P > 0.05) between tree species or water treatments. Imidacloprid concentrations differed (P < 0.001) among plant tissue types, leaves had much greater concentrations (>30×) than any of the other plant tissues. Imidacloprid concentrations in leaves increased steadily throughout the first (2004) growing season, whereas in the year following injection (2005), little imidacloprid was detected in leaves. Samples from outer bark and phloem collected with a cork-borer at 1 m and 2 m above ground line had low levels of imidacloprid as did fine roots. This suggests that imidacloprid translocation occurred mainly in the xylem. When adult A. planipennis were fed leaves from trunk-injected trees, an average of 71% of beetles were killed or intoxicated in 2004 compared with an average of 24% in 2005. Ash species and water treatment had little effect on A. planipennis mortality in either year.