Reversing sodium differentials between the hemolymph and hindgut speeds chill coma recovery but reduces survival in the fall field cricket, Gryllus pennsylvanicus.

Chill-susceptible insects enter the reversible state of chill coma at their critical thermal minimum (CT). During chill coma, movement of Na and water from the hemolymph to the gut lumen disrupt ion and water balance. Recovery from cold exposure requires re-establishment of this balance, and failure to do so results in chilling injury or death. We hypothesized that the passive leak of Na and consequently water during cold exposure is driven by the [Na] differential between the gut and hemolymph. To determine the extent to which this [Na] differential affects cold tolerance, we used artificial diets to load the guts of fall field crickets (Gryllus pennsylvanicus) with various concentrations of Na. Manipulating [Na] differentials had no effect on the CT, agreeing with recent studies demonstrating that chill coma onset precedes loss of ion balance in the cold. A high [Na] diet reversed the direction of the [Na] differential between the gut and hemolymph. Crickets fed a high [Na] diet recovered from 12 h of chill coma nearly twice as fast as those fed low [Na] diets. However, the high [Na] diet was detrimental to survival after prolonged cold exposure (three days at 0 °C). Therefore, while a reduced [Na] differential helps crickets recover from short-term cold exposure, an increased gut Na load itself appears to carry longer-term costs and promotes irreversible chilling injury.