Feeding impairs chill coma recovery in the migratory locust (Locusta migratoria)

- Locusts fed on a high K+ diet had an increased chill coma recovery time, compared to fasted animals, after cold shock.
- Water movement away from the haemolymph causes the initial increase in haemolymph [K+].
- Increased chill coma recovery time was caused by a slower recovery of water, Na+ and K+ balance in fed locusts.
- Reestablishment of [K+]ex and haemolymph volume was decoupled indicating involvement of active K+ transport during recovery.

Low temperature causes loss of neuromuscular function in a wide range of insects, such that the animals enter a state known as chill coma. The ability to recover from chill coma (chill coma recovery time) is often a popular phenotype to characterise chill tolerance in insects. Chill coma in insects has been shown to be associated with a decrease in haemolymph volume and a marked increase in [K+], causing dissipation of K+ equilibrium potential and resting membrane potential. High potassium diet (wheat) has also previously been shown to increase haemolymph [K+] in Locusta migratoria leading to sluggish behaviour. The present study combined these two independent stressors of ion and water homeostasis, in order to investigate the role of K+- and water-balance during recovery from chill coma, in the chill sensitive insect L. migratoria. We confirmed that cold shock elicits a fast increase in haemolymph [K+] which is likely caused by a water shift from the haemolymph to the muscles and other tissues. Recovery of haemolymph [K+] is however not only reliant on recovery of haemolymph volume, as the recovery of water and K+ is decoupled. Chill coma recovery time, after 2 h at −4 °C, differed significantly between fasted animals and those fed on high K+ diet. This difference was not associated with an increased disturbance of haemolymph [K+] in the fed animals, instead it was associated with a slowed recovery of muscle [K+], muslce water, haemolymph [Na+] and K+equilibrium potential in the fed animals.