Cold tolerance strategy and cold hardiness of the invasive zigzag elm sawfly Aproceros leucopoda (Hymenoptera: Argidae)

The invasive sawfly Aproceros leucopoda causes severe defoliation of various elm species and thus can be a major pest in forest stands and urban environments. The overwintering biology of A. leucopoda has not been investigated so far; therefore, the aim of this study was to determine the cold tolerance strategy and cold hardiness of hibernating A. leucopoda eonymphs. The supercooling points (SCPs) of overwintering individuals varied geographically, monthly and interannually and ranged between −12.14 °C and −24.22 °C. As none of the eonymphs survived once the SCP had been reached, A. leucopoda is classified as a freeze-avoidant species. Survival rates of overwintering eonymphs exposed to different sub-zero temperatures above the SCP (−1.6 °C and −4.0 °C for 10, 20 and 30 days and −10.5 °C for 9 days) ranged between 89.2% and 100%, suggesting that A. leucopoda is not a chill-susceptible species. Our results suggest that low winter temperatures may not be expected to be an important limiting factor for the overwintering success of A. leucopoda.