Data from: Plasticity drives extreme cold tolerance of emerald ash borer (Agrilus planipennis) during a polar vortex

Invasive species must often survive combinations of environmental conditions that differ considerably from their native range; however, for a given species it is unclear whether improved tolerance is the result of phenotypic plasticity or genetic adaptation (or both). Agrilus planipennis (Coleoptera: Buprestidae; the emerald ash borer) is an invasive pest of Fraxinus trees in North America and Europe. Previous studies in southwestern Ontario, Canada, showed that A. planipennis is freeze avoidant, preventing internal ice formation by accumulating molar concentrations of glycerol in its hemolymph and depressing its supercooling point (SCP, the temperature at which it freezes). The cold tolerance of these southwestern Ontario animals was used to predict potential distribution, revealing that some Canadian cities should be too cold to allow populations to persist. However, a small population of A. planipennis has persisted in Winnipeg, Manitoba, Canada, through several severe ‘polar vortex’ events. In 2018/19, we collected A. planipennis larvae and prepupae from Winnipeg, Manitoba and Southern Ontario, and found that individuals from Winnipeg were extremely cold tolerant – with SCPs as low as -52 °C in prepupae (compared to 32 °C in Southern Ontario), and survival of unfrozen individuals exposed to -50 °C for one hour. This cold tolerance was accompanied by higher hemolymph osmolality and glycerol concentration than in the SW Ontario individuals. To distinguish between phenotypic plasticity and local adaptation, in 2020/21 we overwintered Winnipeg-sourced individuals either outdoors in southwestern Ontario or in a simulated Winnipeg winter. Simulated Winnipeg winter individuals had cold tolerance similar to those overwintered in Winnipeg, while southwestern Ontario overwintered individuals had cold tolerance similar to those collected previously in the region. The simulated winter individuals had higher hemolymph glycerol concentrations than southwestern Ontario overwintered animals, at least in part due to greater dehydration. Thus, A. planipennis are cold-tolerant enough to survive some of the harshest winters where their host trees can grow, and most likely attain this cold tolerance via phenotypic plasticity. These findings raise the importance of delineating sensitivity of conclusions to unexpected phenotypic plasticity when predicting potential distributions of new invasives or responses to climate change. The data in this dataset are the SCPs and treatment data for the experimental animals used in these cold tolerance experiments.

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