PS 8-72 - Insecticidal treatments mitigate canopy decline from emerald ash borer (Agrilus planipennis) in treated and nearby untreated white ash (Fraxinus americana) trees on the Allegheny National Forest (USA)

Monday, August 15, 2022

5:00 PM – 6:30 PM EDT

Located in: ESA Exhibit Hall

Presenting Author(s)

JB

Jordan D. Bernard

Washington and Jefferson College, United States

Coauthor(s)

JK

Jason S. Kilgore

Associate Professor of Biology
Washington & Jefferson College
Washington, Pennsylvania, United States
KK

Kathleen S. Knight

Northern Research Station, USDA Forest Service, United States
CF

Charles E. Flower

Northern Research Station, USDA Forest Service, United States
AR

Alejandro A. Royo

Research Ecologist
U.S. Forest Service, Northern Research Station, Pennsylvania, United States

Background/Question/Methods

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, and now white ash is listed as Critically Endangered by the IUCN Red List. Prior to its detection on the Allegheny National Forest (ANF) 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 established where 20 randomly selected ash trees started a triennial treatment regime with the injected insecticide emamectin benzoate to conserve ash genetic diversity, test treatment efficacy, observe impacts to surrounding understory vegetation and tree species, and evaluate associational protection (analogous to herd immunity) for untreated trees. We measured ash canopy health (AC; 1 - healthy to 5 - dead) across treated and untreated plots from 2015 to 2021. For this portion of the study, we pooled data by plot and used the Wilcoxon rank-sum test to detect effects of treatment on AC for untreated trees.

Results/Conclusions

Insecticides can be used to directly and indirectly protect white ash trees from EAB-induced decline in canopy health. As expected, 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 2.47-2.55). As predicted by the associational protection hypothesis, untreated ash trees in treated plots remained relatively healthy (mean AC of 3.46, 95% CI of 3.30-3.78). Consequently, patterns of associational protection are beginning to emerge as canopies of untreated ash trees intermix with treated ash remain stable or decline at a slower rate relative to ash in untreated control environments (W=263, P=1.007E-14). 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 white ash.