Cold tolerance and myo-inositol accumulation in overwintering adults of a lady beetle, Harmonia axyridis (Coleoptera : Coccinellidae)

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 -20degreesC in mid-winter. The pattern for seasonal change in tolerance at moderately low temperatures differed among the temperatures exposed: the survival time at -5degreesC peaked in winter, but the time at 5 or 0degreesC peaked in autumn. Because both autumn and winter adults were completely paralyzed only at -5degreesC and survived much longer at 0degreesC than at 5degreesC, the survival time at -5degreesC indicates the degree of chilling tolerance, whereas the time at 5 or 0degreesC 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.