Long-Term Regulation of Sugar Intake by the Blowfly

Abstract

The daily sugar consumption of adult male blowflies. Phormia regina, was individually determined for periods of 5-65 days. Sugars, offered singly and in two-choice situations, were nutritionally useful and highly stimulating, nutritionally useless and highly stimulating, or nutritionally useful and weakly stimulating. The parameter of crop volume was also measured over a 6-day period. The results indicate that a relative constancy in daily sugar intake is maintained at a given sugar concentration and that intake is increased in response to sugar dilution, although a constant weight of sugar intake is not maintained. This regulatory phenomenon is independent of the nutritive value of the sugar being ingested. The only important parameters of the food are its stimulating power and its osmotic pressure. Crop volume also appears to be regulated at a relatively constant level at a given sugar concentration. A homeostatic mechanism for the control of long-term sugar intake is outlined. Its essential element is a negative-feedback relationship between blood osmotic pressure and the rate of food transport through the gut. The finding that daily feed intake and crop volume exhibit a relative constancy is consistent with this hypothesis. Unlike mammals, which measure properties of their food closely related to metabolic value, the fly''s survival depends on the fact that the most prevalent sugars in nature are both highly stimulating and highly nutritious.