Winter Survival and Freeze Tolerance in a Northern Cockroach, Periplaneta japonica(Blattidae : Dictyoptera)
Cold tolerance of overwintering nymphs of a cockroach, Periplaneta japonica, was examined in terms of the supercooling capacity and lower lethal temperature. The supercooling point of overwintering nymphs fell in a relatively narrow range of temperature from -6 to -9℃ and no correlation was observed between the supercooling point and body size. In the temperature range from -5 to -8℃, a significant proportion of cockroaches could tolerate a 12 hr period of tissue freezing. The freeze tolerance capacity differed between nymphal instars, but the supercooling capacity was similar for all nymphs. In a freezing trial at -6 and -7℃, none of the first instar nymphs recovered after tissue freezing, whereas many mid (from 3rd to 5th) and final (8th) instar nymphs survived freezing. Glucose, myo-inositol, scyllo-inositol and trehalose were found in overwintering nymphs, but neither the array nor the content except for trehalose differed among the nymphal instars. Unexpectedly, the concentration of trehalose was negatively correlated to freeze tolerance. Winter survival of this cockroach may be based on both the freeze tolerance and microhabitat selection.