HUNGER-THIRST INTERACTIONS IN THE LOCUST, LOCUSTA-MIGRATORIA

Interactions between food and water intake were investigated by allowi ng 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-ver sa. Fed locusts drank more then unfed controls, by increasing the aver age duration but not the number of drinks in a drinking bout. Likewise , drinking before feeding resulted in larger meals compared with thirs ty 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 d ecreased, most markedly in insects which had drunk before feeding. Loc usts 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 rout e of this flux was not established, Manipulations which provided fluid in the gut while not fully redressing the water deficit, suggested th at reduced meal size in water-deprived locusts could not be accounted for by lack of lubrication in the gut alone. These data suggest that t he major site of interaction between hunger and thirst in locusts is t he haemolymph.