Influence of accumulated growing degree days and relative population density on emerald ash borer body size

Emerald ash borer (Agrilus planipennis Fairmaire, Coleoptera: Buprestidae [EAB]) is an invasive forest pest introduced to North America from Asia most likely in the mid-1990s. Since its introduction, EAB has caused significant mortality in North American ash (Fraxinus spp.). In national survey protocols, the week of initial EAB emergence is typically defined as the accumulation of 450 growing degree days (base 50). Twenty sites were selected in six states (Indiana, Kentucky, Michigan, Missouri, Ohio, West Virginia), nine standard EAB plastic panel traps were deployed at each site, traps were checked bi-weekly, and ten EAB female and male individuals were sub-sampled from each total trap capture for each trap check. Individual body length and mean trap check body weight were measured. Female EAB were significantly larger than males. While there was no significant difference in body size between the lines of latitude for the sites, female body size was significantly smaller at sites north of 40° latitude compared to sites south of 40°. Even though not significantly different, males at sites north of 40° were smaller than those captured south of 40°. The difference in female body size is most likely related to sites north of 40° having larger population sizes, older initial establishment dates, and taking longer to reach 450 accumulated growing degree days than southern sites. Typically, larger female beetles produce more mature eggs than smaller individuals, which will influence population growth dynamics