Effects of larval stage and diapause status on cold hardiness of emerald ash borer (Coleoptera: Buprestidae): implications for winter survival and establishment

Though a minor forest pest in its native range in Asia, the emerald ash borer (EAB), Agrilus planipennis Fairmaire, causes widespread ash (Fraxinus spp) mortality throughout its invaded range in North America and Europe. The rapid range expansion demonstrated by EAB suggests this beetle possesses extraordinary tolerance for a broad range of climatic conditions. While previous studies have measured the cold tolerance of overwintering EAB larvae, none have considered the effect of developmental stage or diapause condition on cold hardiness. By testing the supercooling point (SCP) of lab-reared and field-collected larvae, we evaluated EAB cold hardiness at multiple developmental stages and diapause phases following exposure to different temperature regimes. Results of SCP testing indicated feeding larval stages and larvae in late diapause may be most susceptible to freeze-induced mortality, suggesting that semivoltinism and late-winter freeze events may limit winter survival within EAB populations. Results of field studies confirmed that cold hardiness in EAB is a plastic trait that increases with exposure to lower temperatures, but indicated plasticity may differ between populations. Together, these findings indicate that developmental stage, diapause phase, induction of cold hardiness, and geographic origin may all contribute to the ability of EAB larvae to acclimatize to and survive cold temperatures. Our findings contribute to our understanding of how environmental and physiological factors interact to impact winter survival of EAB and therefore, may improve estimates of the potential invasive range of EAB.