Physiological and biochemical changes in summer and winter diapause and non-diapause pupae of the cabbage armyworm, Mamestra brassicae L. during long-term cold acclimation

Previous studies have demonstrated that cold hardiness in the cabbage armyworm Mamestra brassicae is more developed in winter diapause pupae (WD) than in summer diapause pupae (SD) after short-term cold acclimation. In this study, we investigated specific physiological and biochemical differences between diapause and non-diapause pupae (ND) of M. brassicae after acclimation at 5 °C for up to 4 months. The period required for adult emergence in ND pupae at 20 °C was about 20.2 d and independent of the months acclimated. However, SD and WD pupae reached this level only after 1- and 4-month acclimation, respectively. Levels of respiration (O2 consumption and CO2 release) in ND0 (the subscript indicates the months of acclimation at 5 °C) was eightfold higher than in WD0 and SD0, decreased sharply in ND1 and reached diapause pupae (WD and SD) levels in ND2. Maximal cold hardiness developed during cold acclimation was found in WD3, SD2 and ND2 pupae. During cold acclimation, glycogen content remained at higher levels in WD and SD than in ND. Lipid content in ND decreased but remained high in SD and WD. These results suggest that diapause pupae show large amounts of metabolic reserves in the form of glycogen and lipid during diapause development. To our knowledge, this is the first report to compare the physiological and biochemical differences among summer and winter diapause pupae and non-diapause pupae in the same insect species during long-term cold acclimation.