Hunger-thirst interactions in the Locust, Locusta migratoria

Abstract

Interactions between food and water intake were investigated by allowing 24-h deprived fifth stadium Locusta migratoria L. to take a single meal of dry food (lyophilized grass) then a drink of water or vice-versa. Fed locusts drank more then unfed controls, by increasing the average duration but not the number of drinks in a drinking bout. Likewise, drinking before feeding resulted in larger meals compared with thirsty controls, the increase being due to increased duration of feeding. Rate of ingestion was not significantly influenced in either treatment. While the volume of water ingested during a drinking bout increased when the deprivation period was increased from 24 to 48 h, meal size decreased, most markedly in insects which had drunk before feeding. Locusts given only fresh grass ingested more food (dry wt) and less water than either of the other treatments. Eating dry food was accompanied by a net flow of water from the haemolymph into the crop, but the route of this flux was not established. Manipulations which provided fluid in the gut while not fully redressing the water deficit, suggested that reduced meal size in water-deprived locusts could not be accounted for by lack of lubrication in the gut alone. These data suggest that the major site of interaction between hunger and thirst in locusts is the haemolymph.