Feeding Preferences of Flesh Flies (Sarcophaga bullata) for Sugar-only vs. Sugar-amino Acid Nectars

Abstract

-Fly-pollinated flowers tend to have higher levels of amino acids in their floral nectars than flowers pollinated by other insects. The feeding preferences of flies, over evolutionary time, may account for these high levels of amino acids. To address this hypothesis we examined the behavior of flesh flies (Sarcophaga bullata) when presented with flowers and artificial nectars that contained only sucrose or sucrose and amino acids. Both males and females visited flowers and appeared to feed from them. In the first experiment with artificial nectars, the amino acid component mimicked the combination of amino acids in the nectar of yarrow (Achillea lanulosa). The consumption of the sucrose-only and yarrowmimic nectars was recorded for individual flies. Both male and female flies consumed greater quantities of the yarrow-mimic when they were deprived of a protein source. This difference in consumption disappeared after feeding on liver in both sexes but returned in females after 3 additional days of protein deprivation. These results suggest a nutritional role of amino acids in nectar if flies are protein-deprived in nature. In a second experiment, flies were allowed access to the original yarrow-mimic, two modifications of this nectar containing the same total amino acid concentration, and a sucrose-only nectar. Compared to the sucroseonly nectar, females consumed significantly more of the modified nectar that contained only amino acids that stimulate the fly's sugar receptors. Thus, amino acid-containing nectars may be attractive to flies because they taste sweeter than sugar-only nectar solutions. The discriminatory ability flies showed supports the theory that flies have favored the incorporation of amino acids into floral nectars but studies of fly preferences in nature are needed.