Estimates of emerald ash borer (Coleoptera: Buprestidae) larval galleries in branch samples from asymptomatic urban ash trees (Oleaceae)

Abstract

AbstractAgrilus planipennis (Coleoptera: Buprestidae), is causing extensive mortality of ash (Fraxinus Linnaeus; Oleaceae) in North America. Once detected in an area, resource managers require methods to obtain estimates that could improve management decisions. We studied the within-crown and within-branch distribution and abundance of A. planipennis feeding galleries by sampling 3-m-long branches from asymptomatic urban ash trees and subdividing each branch into 12 sections of 25 cm each. We found galleries in all 12 sections of some, but not all, branches. Section was a significant source of variation in A. planipennis gallery density/m2 of branch surface area. A comparison of predictive power and efficiency of estimates for samples of increasing length, and for samples of the same length but consisting of different combinations of sections, revealed that those based on the two basal 25-cm sections of a branch from the lower-crown or mid-crown of an asymptomatic tree were less accurate and precise than those based on more sections, but were the most cost effective. Whittling more sections per branch, irrespective of the combinations of branch sections per length, improved predictive power but reduced cost effectiveness. We also observed that crown level was not important, and aspect was only marginally so, when estimating gallery abundance per sampled branch.