Regulation of Feeding Behavior in Adult Drosophila Melanogaster Varies With Feeding Regime and Nutritional State

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Abstract
The regulation of feeding behavior in adult Drosophila melanogaster includes such elements as ingestion responsiveness, volume ingested in a single meal, food storage in the crop and rate of defecation. Our results suggest that feeding behavior varies in a manner dependent on feeding regime (food-deprived or ad-libitum-fed) and nutritional state. Fed flies that are subsequently food-deprived become increasingly more responsive to food stimuli over time and, when offered 1% agar diets containing different concentrations of sucrose, ingest greater amounts of diets that have higher sucrose concentrations. When fed ad libitum for 72 h on these same diets, D. melanogaster maintained much smaller crops on average than food-deprived flies fed a single meal. Additionally, ad-libitum-fed flies are grouped into two categories depending on the concentration of sucrose in the diet. Flies fed for 72 h on 1% agar diets having 50 mmoll-1 sucrose or more are not affected by the concentration of sucrose in the diet, while flies fed on diets of 15 or 25 mmoll-1 sucrose increase ingestion responsiveness, crop size and the rate of defecation with decreasing concentrations of sucrose in the diet. Flies fed on even lower sucrose concentrations (5 or 10 mmoll-1 sucrose) for 27-72 h exhibit both a shift over time to larger crop sizes and increased mortality over those of flies fed 15 mmoll-1 sucrose. These data suggest that flies fed ad libitum are capable of modulating their feeding behavior in response to their nutritional state.