Factors influencing the spread of emerald ash borer in urban forests: A case study in Syracuse, New York

The invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) has caused extensive ash (Fraxinus spp.) mortality across the eastern United States. Detection and delimitation of emerging infestations remains difficult due to the stratified dispersal of EAB. The 2013 detection of EAB in Syracuse, NY presented an opportunity to study the distribution and dispersal of an emerging urban infestation and explore factors influencing the spread of EAB. We conducted a delimitation study to determine infestation extent and established transect plots to determine infestation severity. We collected dendrochronological data and within tree larval densities from felled trees throughout the infestation. Surveys revealed the Syracuse infestation to be ~200 km² and stand surveys (n = 78) of infested sites across multiple land use types (greenspaces, right-of-ways, and woodlots) suggested the infestation was most severe where ash comprised >30% of the dominant canopy, with >40% of these ash being infested. Little to no EAB-related mortality was detected, except at two heavily infested sites thought to be the origins of the infestation. Sampled trees (20-90 cm DBH) had a mean larval density of 36 (±24) larvae/m² of phloem. Dendrochronological data indicated the Syracuse area had been infested for seven to ten years. Older infested trees were detected throughout the infestation, suggesting EAB rapidly dispersed once established.