Nutritional Requirements of Axenically Cultured Drosophila Melanogaster Adults

Although much has been done towards defining the nutritional requirements of immature forms of insects (Dougherty, 1959), very little attention has been paid to the needs of adults. Adults of many species can subsist when fed only simple sugar solutions, and this finding has led to many interesting studies of the suitability of various carbohydrates for the maintenance of adult life (see House, 1961) but also, apparently, to neglect of the examination of the requirements for full adult existence, which in the female involves the production of normal numbers of viable eggs. It cannot be assumed that larval and adult nutritional needs are the same, particularly for a species which inhabits different environments as larva and adult. Further, since ability to produce eggs (and sperm) is of primary significance for survival, it is important that the relationship of nutrition to egg production should be studied more extensively than it has been. The purpose of this paper is to do this for the fruit fly (Drosophila melanogaster) whose larval nutritional requirements have already been defined (Sang, 1956, 1959). Only one of the many previous studies of adult nutrition was carried out using axenic culture techniques (Singh & Brown, 1957), and this showed that the anautogenous Aedes aegypti required 'the 10 indispensable amino acids of mammalian nutrition' in order to lay eggs. The vitamins, salts and other nutrients essential for larval growth and development were not needed for egg formation under the conditions of this test. Unfortunately, egg production was measured only during a relatively short period and was at a low level (nine eggs per female in 6 days) so that it is unlikely that stores carried over from the larval stage had been depleted. That such stores do exist in A. aegypti is evident from the work of Dimond, Lea, Hahnert & de Long (1956) who found that a dietary supply of histidine and methionine was not essential for the production of the first few eggs laid by females which had been reared under non-aseptic conditions but fed a defined diet as adults. When these stores were consumed an essential requirement for the two amino acids could be exposed. It was also found that cystine was necessary for a high level of egg production. It follows that similar reserves of vitamins and salts, etc., may have been sufficient to allow the production of the small number of eggs reported by Singh & Brown (1957),