I investigated the seasonal changes of cold tolerance and polyol content in adults of Harmonia axyridis to elucidate their overwintering strategy. Adults decreased their supercooling point and lower lethal temperature only during the winter. Although the seasonal trends for both values were almost consistent, there seemed to be considerable mortality, without being frozen, at -20°C in mid-winter. The pattern for seasonal change in tolerance at moderately low temperatures differed among the temperatures exposed: the survival time at -5°C peaked in winter, but the time at 5 or 0°C peaked in autumn. Because both autumn and winter adults were completely paralyzed only at -5°C and survived much longer at 0°C than at 5°C, the survival time at -5°C indicates the degree of chilling tolerance, whereas the time at 5 or 0°C seems to show starvation tolerance. This beetle accumulated a relatively large amount of myo-inositol during winter. Myo-inositol content synchronized seasonally with supercooling capacity, the lower lethal temperature and the chilling tolerance, suggesting that myo-inositol may play some role in the control of cold tolerance in this beetle.
We investigated the physiological adaptations for winter survival in a freeze-intolerant chrysomelid, Aulacophora nigripennis, in warm-temperate regions. The adults showed a decreased supercooling point (SCP), increased chill tolerance and high myo-inositol content during winter. Chill tolerance at 0°C appears to be a more suitable indicator of their cold hardiness than SCP because they die at 0°C without freezing and normally an not exposed to subzero temperatures below their SCP., Masahiko Watanabe, Kazuhiro Tanaka, and Lit