Cold hardiness of emerald ash borer (Agrilus planipennis) from green and black ash

The emerald ash borer (EAB), Agrilus planipennis Fairmaire, is native to Asia and is spreading in North America. Populations in Minnesota are at the leading, northwestern edge of its distribution. Minnesota has more ash (Fraxinus spp) than any other state. Most of these are black ash (Fraxinus nigra) in the northern part of the state. Northern Minnesota frequently has temperatures that fall below -30°C. The threat EAB poses in this unique environment depends, in part, on EAB’s cold hardiness, its ability to survive cold temperatures. Previous cold hardiness studies have focused on EAB from green ash (Fraxinus pennsylvanica) or unspecified Fraxinus spp. The objective of this study is to compare the cold hardiness of EAB from green ash and black ash using supercooling points (SCP) of “j-stage” larvae, the prepupal overwintering stage. Adult EAB were obtained from naturally-infested green ash logs from Minnesota. Adults were mated in rearing containers in the laboratory and fed green ash foliage. Neonates were manually inserted into green ash or black ash logs collected from the same stand in Grand Rapids, MN. Larvae were allowed to develop for 4 months and extracted. SCPs were measured using thermocouple thermometry. Mean SCP for larvae from green ash was -22.1°C±3.32 and did not differ for larvae from black ash. (-24.8°C±0.87) However, larvae from green ash exhibited a wider range of SCPs (-12.34°C to -27.13°C) than larvae from black ash (-22.02°C to -26.65°C). These results show that host species does not greatly influence EAB’s ability to overwinter.