Estimating local spread of recently established emerald ash borer, Agrilus planipennis, infestations and the potential to influence it with a systemic insecticide and girdled ash trees

• A. planipennis spread was estimated from a 5 yr project encompassing >390 km2.
• Spread rates of a small and a large infestation were 0.4–0.7 and 1.2–1.7 km yr−1.
• A simple descriptive model and a simulation model are used to describe the spread.
• Simulations indicated a reduced spread of EAB out of areas containing girdled trees.

Information on the pattern and rate of spread for invasive wood- and phloem-feeding insects, including the emerald ash borer (EAB) (Agrilus planipennis Fairmaire), is relatively limited, largely because of the difficulty of detecting subcortical insects at low densities. From 2008 to 2011, grids of girdled and subsequently debarked ash (Fraxinus spp.) detection trees were established across a >390 km2 area encompassing two recently established EAB infestations in Michigan as part of the SLow Ash Mortality (SLAM) Pilot Project. Ash distribution and abundance were inventoried across the project area which included public and private forestland, a state park, and street trees in a small municipality. Spread rates of EAB from 2008 to 2011, based on larval presence in girdled detection trees, were estimated to be 1.2–1.7 km yr−1 in the larger, presumably older, infestation and 0.4–0.7 km yr−1 in the smaller infestation; suggesting a slower spread rate during the initial stages of population establishment. From 2009 to 2011, a total of 587 ash trees in the project area were trunk-injected with a highly effective, systemic emamectin benzoate insecticide. Potential effects of girdled ash trees and the systemic insecticide treatment on EAB spread were evaluated using a simulation model and a simple descriptive model of observed spread. Not surprisingly, density of trees treated with the insecticide was too low to exert a detectable effect on EAB spread. However, while the density of girdled trees was also relatively low, model results indicated a reduced spread of EAB out of areas containing girdled trees.