INFLUENCE OF MOISTURE CONTENT AND TEMPERATURE ON COLD-HARDINESS OF HIBERNATING INSECTS

Abstract

Moisture content affected cold-hardiness, measured as ability to supercool, only to the extent that it affected the concentration of body fluids and hence their freezing points. Supercooling remained approximately constant in amount over a wide range of moisture conditions. Only when desiccation was severe did it produce appreciable cold-hardening. Chilling at constant low temperatures was effective in increasing the cold-hardiness of Bracon cephi (Gahan), ineffective in Melanoplus bivittatus (Say) and Cephus cinctus Nort., and of doubtful effect in Loxostege sticticalis (L.). The variable temperatures of the natural environment produced significant cold-hardening in all four species; occasional periods of developmental temperatures are considered more likely to be responsible than chilling. Blood density appeared to be related to cold-hardiness, but its ready response to other factors obscured the relationship.