Regulation of water ingestion by the locust, Chortoicetes terminifera: the effect of injections into the haemolymph

Adults of the locust Chortoicetes terminifera which had been deprived of water for 24 h took larger 'meals' of water than insects which had been deprived for 2 h. Water or dilute solutions of NaCl injected into the kaemcoel reduced the amount of water ingested by 24-h, deprived locusts. Injections of more concentrated solutions of NaCl (0.5 m) or glycerol (1.0m) increased the water intake of 2-h deprived locusts. Water injections into 24-h deprived locusts did not reduce their responsiveness to sucrose and it is concluded that haemolymph osmotic pressure plays an important role in determining the specific responsiveness of C. terminifera to water. The time course of the effects of injection indicates that the effects of haemolymph osmotic pressure on water responsiveness are mediated neurally. Injections of water into 24-h deprived insects caused a marked reduction in the sizes of their meals of seedling wheat. It is suggested that the mechanisms responsible for the regulation of water intake might limit total intake when locusts have access only to fresh vegetation of high water content.