Effects of cold stress during pupal diapause on the survival and development of Mamestra configurata (Lepidoptera: Noctuidae)

The effects of exposing diapausing pupae of Mamestra configurata Wlk. to temperatures from -5° C to-20° C during a 140-day experimental period were reduced survival to post-diapause stages, reduced survival to emergence as malformed or normal adults, and a reduced rate of post-diapause development. Pupae given a continuous exposure of variable length to -10° C and pupae given the same exposure to -10° C, interrupted by 28 days at 0° or -5° C, had the same survival, indicating that repair of cold injury does not occur at 0° or-5° C. Assuming that the effects of low temperatures were additive, not only for exposures to one temperature but also for exposures to different combinations of temperatures, survival was decribed by a polynomial: $$\begin{gathered} 1n(p/1 - p) = 3.12 - 0.00834t_{ - 5} \hfill \\ - 0.0515 t_{ - 10} - 0.346 t_{ - 15} - 2.00 t_{ - 20} , \hfill \\ \end{gathered}$$ where p=the proportion in post-diapause stages and t=the number of days of exposure to the temperature given by the subscript. The values of the coefficients (C) were inversely related to the temperature of exposure (T): log₁₀ C=-2.87-0.159 T. In validation experiments, the model accurately predicted survival of pupae in the laboratory and in soil under natural snow-cover or in soil where snow cover was maintained at <2 cm through a complete winter. Our results suggest that: (1) symptoms of cold injury, from death in the stage exposed through death, malformation or retarded development in post-exposure stages represent a continuum that can be produced by varying the exposure time at temperatures that cause cold injury; (2) repair does not occur at these temperatures nor at slightly warmer temperatures (e.g. at 0° C for M. configurata pupae); (3) the total amount of injury is not affected by the sequence of temperatures to which the insect is exposed; (4) freezing is not responsible for the observed cold injury.