Cold tolerance of Panonychus citri (McGregor) (Acari: Tetranychidae)

The citrus red mite (CRM), Panonychus citri (McGregor) (Acari: Tetranychidae), has expanded its range from southern China to colder regions in northern China, where low winter temperatures pose a critical survival challenge. Understanding its cold tolerance is important for predicting future distribution and dispersal patterns in northern China. However, the cryobiology of CRM remains poorly characterized. This study investigated three key aspects: (1) supercooling points (SCPs) of adult females, (2) lethal low temperatures for eggs and adult females under acute cold exposure and (3) the effects of cold acclimation (20 °C for 1-3 generations) and rapid cold hardening (4 °C for 2 h) on adult female cold tolerance. Results showed that the average SCP of adult females was - 20.66 ℃. Eggs exhibited significantly stronger cold tolerance than adult females. The lethal temperature causing 50% mortality (LT₅₀) was expected as -17.70 °C for eggs and - 7.58 °C for adult females after 2 h exposure. Notably, 6.03% of eggs survived 5 h at -31 °C, whereas all adult females died within 1 h at -12 °C. Both rapid cold hardening and multi-generational cold acclimation significantly enhanced adult female cold tolerance. Adult females were chill susceptible, and their cold tolerance could not be measured by SCP. These findings provide crucial physiological benchmarks for CRM. However, accurately forecasting its northward expansion requires future studies that integrate these laboratory data with field validation and modeling of ecologically relevant temperature regimes.