Rapid responses to high temperature and desiccation but not to low temperature in the freeze tolerant sub-Antarctic caterpillar Pringleophaga marioni (Lepidoptera, Tineidae)

A broad definition of rapid cold hardening (RCH) is that it is the process whereby insects increase their survival of a sub-zero temperature after a brief (h) pre-exposure to a less severe low temperature. The effects of various pre-treatments on survival of two h at -7.9°C were investigated in the freeze tolerant sub-Antarctic caterpillar Pringleophaga marioni (Lepidoptera: Tineidae), the first time RCH has been investigated in a freeze tolerant arthropod. All caterpillars froze when exposed to -7.9°C, and none of the low temperature pre-treatments (-5, 0, 5 and 15°C, as well as -5°C and 0°C with a delay before freezing) nor slow cooling (0.1°C/min) elicited any improvement in survival of -7.9°C as compared to controls. However, high temperature treatments (25, 30 and 35°C), desiccation and acclimation for 5 days at 0°C did result in significant increases in survival of the test temperature, possibly as a result of heat shock protein production. Haemolymph osmolality was elevated only by the 35°C pre-treatment. It is suggested that the unpredictable environment of Marion Island means that P. marioni must always be physiologically prepared to survive cold snaps, and that this year-round cold hardiness therefore supersedes a rapid cold hardening response.