Effects of rapid cold hardening in different intensities on the physiological indices related to cold tolerance in adults of Ophraella communa (Coleoptera: Chrysomelidae).
Aim: As an effective approach adapting to acute temperature fluctuation and short-term cold shock, rapid cold hardening (RCH) can enhance cold resistance of some insects in a very short period. We explored the physiological mechanisms responding to RCH in different intensities in Ophraella communa, which is a promising biological control agent for invasive Ambrosia artemisiifolia. Methods: O. communa adults were subjected to different intensities of RCH, including being exposed to -4, 0, 4 and 8°C for 4 h, or exposed to 0°C for 1, 4, 8 and 16 h. The contents of cryprotectants and the activities of protective enzymes were measured. Results: The supercooling point (SCP) of O. communa adults was significantly depressed by RCH (P<0.05), particularly at 0°C/4 h, with the exception of the groups of 8°C/4 h, 0°C/1 h and 0°C/8 h. With the augment of RCH intensity (decrease of the treated temperature or increase of the sustained time), the glycerol content and the activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) changed notably, especially at 0°C/4 h, though water and sugar contents were not significantly changed by RCH. Conclusion: There exist the threshold and the optimum induction intensity of RCH in O. communa adults, and excessive intensities may be harmful for enhancement of cold tolerance in O. communa adults. The results are helpful to better understanding the overwintering strategies of O. communa and the artificial cultivation of cold-tolerant population.