Adult Tephritidae, especially of the genus Anastrepha (Schiner, 1868), have been observed to feed on a wide variety of natural diets. The fruit on which they feed, in general, are rich in sugar content, chiefly glucose, frutose and sucrose, which are also the sugars that those insects utilise better. Neither the behavioural mechanisms, nor the physiological ones, that control food selection by insects, are well known. Because some of those aspects are not known for the species Anastrepha obliqua (Macquart, 1835) either, and in order to understand their biology better, three experiments were conducted. In the first experiment, it was checked whether there was a difference in metabolic profit by those insects, when fed the carbohydrates more frequently found in nature, as resulting in a bigger egg production and higher survival rate at the end of the experiment. In the second, it was checked whether A. obliqua can regulate diet ingestion according to carbohydrate content in dry as well as wet diets. In the third experiment, measurements were made to establish the lowest carbohydrate concentration flies are able to recognise in the diet. Analysis of the data showed that ingestion of carbohydrates which are commonly found in nature, in association with a protein source, is very well utilised by females of A. obliqua. It was also shown that .those insects are not probably able to compensate for the difference in carbohydrate content in dry diets, whereas they do so for wet diets. In relation to discrimination threshold, it seems that it is related to the higher occurrence of the carbohydrate in their normal diet, that is, they can recognise carbohydrates that are common in their natural diet better than the less frequent ones.