Adult feeding by holometabolous insects: pollen and nectar as complementary nutrient sources for Rhingia campestris (Diptera: Syrphidae).

Examination of the gut contents of adult Rhingia campestris reveals that there are considerable differences in the relative amounts of pollen and nectar ingested by individual insects. Pollen, a rich protein source, is required most by females, particularly during those stages of ovarial development when yolk deposition occurs. Nectar, which is mainly carbohydrate, is required in large amounts by males, and is also required by females before and after oogenesis. These results are discussed in relation to the likely nutritional needs of the flies, and it is suggested that similar feeding patterns may be found in a variety of other flower visiting insects. Finally, reference is made to the problems of making ecological assumptions about feeding behaviour on the basis of the morphological attributes of the mouthparts.