REGULATION OF FEEDING-BEHAVIOR IN ADULT DROSOPHILA-MELANOGASTER VARIES WITH FEEDING REGIME AND NUTRITIONAL STATE

The regulation of feeding behavior in adult Drosophila melanogaster in cludes such elements as ingestion responsiveness, volume ingested in a single meal, food storage in the crop and rate of defecation. Our res ults suggest that feeding behavior varies in a manner dependent on fee ding regime (food-deprived or ad-libitum-fed) and nutritional state. F ed flies that are subsequently food-deprived become increasingly more responsive to food stimuli over time and, when offered 1% agar diets c ontaining different concentrations of sucrose, ingest greater amounts of diets that have higher sucrose concentrations. When fed ad libitum for 72h on these same diets, D. melanogaster maintained much smaller c rops on average than food-deprived flies fed a single meal. Additional ly, ad-libitum-fed flies are grouped into two categories depending on the concentration of sucrose in the diet. Flies fed for 72h on 1% agar diets having 50mmol l(-1) sucrose or more are not affected by the con centration of sucrose in the diet, while flies fed on diets of 15 or 2 5 mmol l(-1) sucrose increase ingestion responsiveness, crop size and the rate of defecation with decreasing concentrations of sucrose in th e diet. Flies fed on even lower sucrose concentrations (5 or 10mmol l( -1) sucrose) for 27-72h exhibit both a shift over time to larger crop sizes and increased mortality over those of flies fed 15 mmol l(-1) su crose. These data suggest that flies fed ad libitum are capable of mod ulating their feeding behavior in response to their nutritional state.