Sectored distribution of trunk-injected 14C imidacloprid in Fraxinus spp. trees and effects on male and female emerald ash borer (Agrilus planipennis) behavior and mortality

Imidacloprid applied as a trunk injection is often used to control emerald ash borer (Agrilus planipennis Fairmore, Coleoptera: Buprestidae) (EAB) but effectiveness can be variable. We determined the extent to which movement of imidacloprid is sectored within the trunk of ash trees and how this might affect EAB behavior and mortality. We injected Fraxinus spp. trees with ¹⁴C labeled imidacloprid either directly below a branch in the first whorl or at a right angle to the first whorl branches. Leaves were sampled and bioassays were performed through two growing seasons. Imidacloprid equivalent concentration (IEC) in leaves varied with time and orientation to injection point. We conclude that ash trees have a zigzag pattern of xylem flow which could lead to variable IEC in the tree crown. During 2007, the year after injection, IEC in leaves from spring-injected trees was greatly reduced as was insect mortality.