Cold tolerance and egg diapause shape overwintering success in Aedes koreicus mosquitoes

Aedes koreicus, a temperate mosquito native to East Asia, is rapidly expanding across Europe. While diapause is documented in this species, the combined effects of temperature and exposure duration on egg overwintering success remain poorly understood. We experimentally quantified the hatching success of diapausing and non-diapausing Ae. koreicus eggs exposed to five fluctuating cold regimes (ranging from 5 °C to -20 °C) for periods of 2 to 30 days, using a constant 5 °C control. Under control conditions, hatching success was similar between both egg types. However, cold exposure markedly reduced success, with non-diapausing eggs experiencing a significantly stronger decline (0.343 ± 0.029 SE) than diapausing eggs (0.487 ± 0.031 SE). Generalised linear beta-binomial models revealed a strong, nonlinear interaction between temperature, exposure duration, and egg type. Notably, diapausing eggs exhibited a hatching peak at intermediate subzero temperatures (-5 °C to -10 °C) and maintained higher success during prolonged cold exposure. Conversely, non-diapausing eggs were substantially more sensitive, showing sharper declines across the thermal gradient. These results align with the overwintering strategies of other temperate Aedes species, such as Ae. albopictus, and emphasize the necessity of considering both temperature and duration when assessing cold tolerance. Our findings provide essential parameters for phenological modeling and improve predictions of Ae. koreicus invasion potential in colder regions under variable climatic conditions.