Phenology and Voltinism of Emerald Ash Borer (Coleoptera: Buprestidae) in Central North Carolina

Abstract

The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), has killed millions of ash (Fraxinus spp.) trees across North America. Classical biological control using introductions of parasitoid wasps may provide a sustainable approach to managing this invasive insect. However, the establishment of parasitoids in the southern United States has been difficult. The phenology of emerald ash borer was studied in central North Carolina to inform biological control efforts that better align with the seasonal availability of susceptible emerald ash borer life stages in the warm climate of this region. Biweekly emerald ash borer life stage assessments were conducted in stands of infested green ash (Fraxinus pennsylvanica Marshall, Lamiales: Oleaceae) over 26 consecutive months (June 2019 through August 2021). Adult trapping was also conducted in these stands in the spring and summer of 2019, 2020, and 2021. Based on these collections, emerald ash borer exhibits a univoltine (1-yr) life cycle. Parasitoid-susceptible larvae (third and fourth instars in galleries) are present from late June through October (~1,100–3,000 degree days base 10ºC) and are mostly absent during the remainder of the year. Parasitoid release timings and the life history of selected parasitoid species should be aligned with this window of host availability to be effective. This characterization of emerald ash borer phenology and voltinism will help improve the timing and effectiveness of management efforts as this forest pest continues to spread in southern North America.

Size of emerald ash borer in North Carolina,USA: Preliminary evidence for a sawtooth cline?

“…North Carolina appears to be at or near a geographic life cycle transition point where nearly all EAB larvae develop to a prepupal stage in a single year, that is, EAB is univoltine (Bohannon, 2022;Bohannon et al, 2022;Nalepa et al, 2021). The current results indicating that EAB body size in NC is smaller than expected if it were to fit a converse Bergmann's cline may be associated with this life cycle shift.…”

“…A univoltine life cycle also has major implications for developing a successful biological control program for EAB at southern latitudes. This is because, in a given year, larval stages susceptible to parasitism (typically third and fourth instars) are not abundant prior to the reproduction of adult EAB emerging in a population (Bohannon et al, 2022). This constrained seasonal availability of parasitoid‐susceptible EAB larvae would reduce appropriate host material for spring‐emerging parasitoids, potentially preventing the successful establishment of these parasitoid species (Bohannon, 2022; Bohannon et al, 2022; Gould et al, 2020; Nalepa et al, 2021).…”

“…A univoltine life cycle also has major implications for developing a successful biological control program for EAB at southern latitudes. This is because, in a given year, larval stages susceptible to parasitism (typically third and fourth instars) are not abundant prior to the reproduction of adult EAB emerging in a population (Bohannon et al, 2022).…”

“…This constrained seasonal availability of parasitoid-susceptible EAB larvae would reduce appropriate host material for spring-emerging parasitoids, potentially preventing the successful establishment of these parasitoid species (Bohannon, 2022;Bohannon et al, 2022;Gould et al, 2020;Nalepa et al, 2021).…”

“…Because of the location of its initial invasion, most studies on the biology and life history of EAB have been implemented in the northern United States. Regional climatic differences, however, may affect the applicability of these results to other geographic regions of the country (e.g., Abell et al, 2019;Bohannon, 2022;Bohannon et al, 2022;Nalepa et al, 2021). Emerald ash borer was first detected in North Carolina (NC) in 2013 and is now reported from 63 counties in the state.…”