Regulation of Supercooling and Nucleation in a Freeze Intolerant Beetle (Tenebrio molitor)’

The mealworm beetle, Tenebrio m&or (Tenebrionidae, Coleoptera), is a freeze-susceptible species that does not survive cooling to below the supercooling point (i.e., tissue freezing) in any stage of development. Most insects of a given age and developmental stage exhibit a relatively narrow range of supercooling point (SCP) values. However, Tenebriu larvae reared at 24°C on dry wheat bran displayed a wide range of values extending from I.5 to -24.3”C. Larvae acclimated at 5°C had slightly lower SCPs; however, the range of individual values remained highly variable. SCPs were significantly correlated (r = 0.59) with body weight: small larvae demonstrated a greater capacity for supercooling than larger individuals. In an attempt to identify the specific site of nucleation, the SCPs of hemolymph, fat body, and gut contents were determined and compared to whole body SCPs. Hemolymph and fat body samples generally supercooled to 15°C or lower for larvae whose whole body SCPs were -5°C or higher. Only on some occasions could whole body SCPs be explained on the basis of the efficacy of ice nucleators within the gut. o 1990 Academic PWS, IIIC.