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Survival of cabbage stem flea beetle larvae, Psylliodes chrysocephala, exposed to low temperatures

The cabbage stem flea beetle, Psylliodes chrysocephala (L.) (Coleoptera: Chrysomelidae), is a major pest of winter oilseed rape. The larvae live throughout winter in leaf petioles and stems. Winter temperatures might play an important role in survival during winter and hence population dynamics, yet to what degree is unknown. This study investigates the effect of exposure time, cold acclimation, and larval stage on survival at −5 and −10 °C. Exposure time at −5 °C was 1, 2, 4, 8, 12, 16, and 20 days and 6, 12, 24, 36, 48, 72, 96, 120, and 144 h at −10 °C. Mortality increased with increasing exposure time and was significantly lower for cold‐acclimated larvae. Estimated time until an expected mortality of 50% (LT50) and 90% (LT90) of larvae exposed to −5 °C was 7.4 and 9.6 days (non‐acclimated) and 11.0 and 15.1 days (acclimated), respectively. Estimated LT50 for non‐acclimated and acclimated larvae exposed to −10 °C was 32.6 and 70.5 h, respectively, and estimated LT90 66.8 and 132.2 h. Significant differences in mortality between larval stages were observed only at −5 °C. When exposed to −5 °C for 8 days, mortality of first and second instars was 81.2 and 51.3%, respectively. When exposed to −10 °C for 2 days, mortality of first and second instars was 70.5 and 76.1%. Data on winter temperatures in Denmark from 1990 to 2013 showed that larvae were rarely exposed to a number of continuous days at −5 or −10 °C causing a potential larval mortality of 50–90%.