THERMAL-HYSTERESIS-FACTORS IN OVERWINTERING INSECTS

The haemolymph of 9 species of insects found overwintering under the bark of dead trees in northern Indiana contained factors which produced a thermal hysteresis (a difference between the freezing and melting points) of several degrees. These thermal-hysteresis-factors were common in overwintering beetles, but rare in non-Coleoptera, and are similar to the macromolecular antifreezes of polar marine teleost fishes. The factors were found in both freeze-susceptible and freeze-tolerant species, and their function in freeze-susceptible insects appears to be to depress the supercooling points and therefore the lower lethal temperatures of the insects. However, the function of the factors in freeze-tolerant species is not clear. Possible functions are discussed. © 1979.