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Contributed Talk

Session: : Conservation Ecology and Extinction 3

COS 213-6 - Insecticidal treatments confer associational protection for untreated white ash (Fraxinus americana) against emerald ash borer (Agrilus planipennis) on the Allegheny National Forest (USA)

Wednesday, August 9, 2023
4:45 PM – 5:00 PM PDT
Location: C125-126
Abstract: Emerald ash borer (EAB, Agrilus planipennis) has decimated ash (Fraxinus spp.) across eastern hardwood forests of North America since its discovery in Michigan in 2002 with the hosts rapidly approaching functional extirpation throughout the range of EAB invasion. Prior to its detection on the Allegheny National Forest (ANF) of Pennsylvania in 2013, 193 plots across a range of ash densities were established in 2010 on the ANF to monitor white ash (F. americana) decline and mortality. In 2015, 27 plots (3.14 ha) were chosen in which 20 randomly selected ash trees started a triennial treatment regime with the injected insecticide emamectin benzoate to conserve ash genetic diversity, test treatment efficacy, and evaluate associational protection (analogous to herd immunity) for untreated trees. We measured ash canopy health (AC; 1 - healthy to 5 - dead) across these 27 treated and 107 untreated (control) plots from 2015 to 2021. For this portion of the study, we pooled trees by plot and treatment and used the Wilcoxon rank-sum test to detect a difference in canopy health between control trees and untreated trees in treated plots.


By 2021, untreated ash trees in control plots had succumbed to EAB (mean AC of 4.73, 95% CI of 4.60-4.87), while insecticide-treated ash trees remained healthy (mean AC of 2.52, 95% CI of 2.33-2.71). As predicted by the associational protection hypothesis, untreated ash trees in treated plots (mean AC of 3.46, 95% CI of 3.22-3.70) performed better than untreated trees in control plots. Consequently, patterns of associational protection are beginning to emerge as canopies of untreated ash trees in plots containing treated trees decline at a slower rate relative to ash in untreated (control) environments (W=263, P=1.007E-14). Effects of the initial health of the trees, ash density, landscape position, and tree size on insecticide treatment efficacy and associational protection is also being examined. Overall, insecticides can be used to directly and indirectly protect white ash trees from EAB-induced decline in canopy health. Judicious application of insecticide to treat a portion of ash trees in an area could prevent or slow the loss of genetic diversity and possibly extinction of ash trees in natural stands.