Metabolism of the sub-Antarctic caterpillar Pringleophaga marioni during cooling, freezing and thawing
Although general models of the processes involved in insect survival of freezing exist, there have been few studies directly investigating physiological processes during cooling, freezing and thawing, without which these models remain hypothetical. Here, we use open-flow respirometry to investigate the metabolism of the freeze-tolerant sub-Antarctic caterpillar Pringleophaga marioni Viette (Lepidoptera: Tineidae) during cooling, freezing and thawing and to compare animals exposed to non-lethal (-5.8°C) and lethal (-6.0°C, after which caterpillars are moribund for several days, and -18°C, after which caterpillars are completely unresponsive) freezing stress. We found a large decrease in metabolic rate (that is not associated with freezing) at -0.6±0.1°C and calculated a Q10 of 2.14×10 3 at this breakpoint. This breakpoint is coincident with the critical thermal minimum (CTmin) and is hypothesised to be a metabolic manifestation of the latter, possibly a failure of the Na+/K +-ATPase pump. This provides a plausible link between processes at the cellular level and observations of the action of the CTmin at tissue and whole-organism levels. Caterpillars froze at -4.6±0.1°C and had detectable metabolism when frozen. Post-thaw, metabolic rates were lower than pre-freering measurements. Post-thaw metabolic rates did not differ between temperatures that did and did not kill the caterpillars, which suggests that mortality may be a result of a breakdown in processes at the organismal, rather than cellular, level of organisation.