SEPARATING FOOD AND WATER-DEPRIVATION IN LOCUSTS - EFFECTS ON THE PATTERNS OF CONSUMPTION, LOCOMOTION AND GROWTH

In a factorial experiment, fifth-instar Locusta migratoria (L.) (Ortho ptera: Acrididae) were given either dry food (lyophilized grass) and d rinking water, food only, water only, or neither food nor water. Food consumption and insect weight were measured daily, and the behaviour o f each locust was recorded for 5 h on each of four consecutive days an d for 2.5 h on the fifth. Consumption declined progressively in locust s given food only, and those given water only were not observed to dri nk after the first day of food deprivation. The decline in food consum ption on the first day was accounted for by a decrease in the average duration of feeds, which remained constant thereafter. The further dec line in consumption over subsequent days was due to a progressive decl ine in the number of feeds. Although food availability did not slow we ight loss relative to locusts given neither food nor water, the availa bility of water without food did. The proportion of time locomoting in creased in all deprivation treatments, but the pattern of change acros s the five observation days differed markedly between treatments. Locu sts given food but no water increased locomotion from 20% of the time budget (the value for controls) to 30% on the first day of deprivation , and by the second day had reached a plateau of approximately 65%, wh ich was maintained until the experiment was terminated on day 5. In co ntrast, locusts given water but no food approached the 65% level of lo comotion on the first day, which was statistically greater than the 55 % observed in those deprived of both food and water. This increase was due both to an increase in the number of locomotion bouts initiated a nd an increase in the average duration of locomotion bouts. On the sec ond and third days, all deprivation treatments maintained locomotion a t around 65%. By day 4, locomotion had decreased to approximately 15% in locusts deprived of both food and water, but not in those deprived of food only or water only. Unlike these given only food, locusts give n only water showed a reduction in locomotion of c. 15% on the fifth d ay.