Cold tolerance of European populations of Drosophila suzukii varies among seasonal phenotypes

The invasive Asian fruit fly Drosophila suzukii is a significant pest of soft and stone fruits in large parts of the world, including Europe. Understanding its performance at low temperatures is crucial for establishing sustainable management programs. In this paper, we compared the cold tolerance of summer-acclimated (developed at 25 °C, 16:8 h (L:D)) and winter-acclimated (developed at 10 °C, 8:16 h (L:D)) males and females of one Southern European (Spanish) and two northern European (Belgian) populations by means of two common indices: (1) the lower lethal temperature (LLTemp) and (2) the lower lethal time (LLtime). Winter-acclimated D. suzukii adults proved to be substantially more cold tolerant than summer-acclimated adults. Their LLtime50 values were significantly longer than those of summer-acclimated flies and this was the case for all tested temperatures. Winter-like acclimation also resulted in more negative LLTemp values. Non-uniform differences in cold susceptibility between males and females were found, depending on the exposure conditions and the treatment groups. Variations in cold tolerance among Belgian and Spanish populations were observed too, albeit these were more likely ascribed to variations among individuals than to variations due to geographic origin and adaption. Overall, our results indicate that phenotypic plasticity in the field can strongly increase the low temperature performance of D. suzukii, thereby facilitating its overwintering success in temperate climates.