Effects of low temperature stress on the supercooling capacity and development of Galeruca daurica Joannis larvae(Coleoptera: Chrysomelidae)
Author of the article:LI Hao1** ZHOU Xiao-Rong1 PANG Bao-Ping1*** ZHANG Zhuo-Ran2CHANG Jing1 SHAN Yan-Ming2
Author's Workplace：1. Research Centre for Grassland Entomology, Inner Mongolia Agricultural University, Hohhot 010019, China; 2. Inner Mongolia Grassland Station, Hohhot 010020, China
Key Words：Galeruca daurica, low temperature stress, developmental duration, survivorship
Abstract：[Objectives] Low temperature is one of key factors affecting the growth, development and survivorship of insects. We investigated the effects of low temperature stress on the supercooling capacity and development of Galeruca daurica Joannis larvae in order to build an indispensable foundation for further forecasting its population dynamics and distribution. [Methods] We measured the supercooling points (SCPs), developmental duration and survival rates of larvae and pupae after first instar larvae had been subjected to different low temperature treatments in the laboratory. [Results] Rapid cold hardening significantly influenced the SCPs of first instar larvae. The SCP of larvae exposed to ﹣10℃ for 2 h was significantly lower than that of control larvae, whereas the SCP of larvae exposed to ﹣6℃ for 2 h was not. The SCPs of second instar larvae that had been subjected to low temperature treatment as first instars were not significantly different from those of the control. The developmental durations of the first and second instar larvae, and the overall larval developmental period, were significantly longer than those of the controls if first instar larvae had been subjected to low temperature. Cold treatment of the first instar, however, had no significant effect on the duration of the pupal stage. Short (2 h) low temperature (﹣5℃) treatments did not significantly affect the developmental duration of third instar larvae but longer (2-6 d) low temperature treatments did. Longer exposure to 0℃ did not affect developmental duration. Low temperature treatment significantly affected the death rates of first and second instars, but not of third instars and pupae. Generally, the lower the temperature and the longer the period of exposure, the longer the developmental duration and the higher the death rate of successive instars and pupae. [Conclusion] Low temperature stress can significantly enhance the supercooling capacity of G. daurica larvae but also prolongs development and reduces the survival rates of successive instars. The longer the period of exposure and the lower the temperature, the stronger the effect.