Insect cold tolerance is critical for overwintering survival. Chrysoperla nipponensis (Okamoto) (Neuroptera: Chrysopidae), a dominant natural enemy in biological control, was studied to investigate its cold tolerance mechanisms for effective conservation. Three diapause states were simulated. Excluding temperature effects, diapause induction significantly enhanced cold tolerance, which increased progressively with diapause depth. The supercooling point (SCP) and freezing point (FP) during stable diapause were significantly lower than during induction, indicating superior low-temperature tolerance. Although photoperiod treatments showed no significant differences in SCP and FP of 5-d adults, the 24-h low-temperature survival rate was significantly higher during diapause induction than in the non-diapause state. Glycerol content increased significantly during diapause and positively correlated with cold tolerance. RNA interference of the glycerol kinase gene CnGK2 significantly reduced both glycerol content and low-temperature survival, demonstrating that CnGK2 promotes glycerol accumulation to improve cold tolerance. This work provides a foundation for enhancing overwintering protection and spring biocontrol efficacy of this commercially important natural enemy.
Cui et al. (Thu,) studied this question.