Elemental stoichiometry of Drosophila and their hosts

1. Nitrogen (N) and phosphorus (P) availabilities are important ecological determinants of resource use in nature, Despite the wide range of hosts use d by species of the genus Drosophila, elemental composition of natural reso urces of these flies has never been investigated. 2. Total body N and P contents were determined in seven species of wild-cau ght Drosophila, their natural hosts, and artificial diets routinely used to rear these flies in the laboratory. The flies tested included D. hydei, D, arizonae, D. simulans and D. pseudoobscura collected from rotting fruit (m elons), and the cactophilic D. nigrospiracula, D. mojavensis and D. pachea collected from their specific host plants, Saguaro, Organpipe and Senita ca ctus, respectively. 3. Natural hosts varied in elemental composition, with fruit showing higher N (2.8-4.3% dry mass) and P (0.50-0.67%) levels compared with cacti (0.5-1 .6% N; 0.01-0.29% P). No consistent differences in N and P levels were foun d between healthy and necrotic cactus tissue. 4. Total body N and P also varied among Drosophila species. This variation mirrored the levels of N and P found in the respective hosts and laboratory diets. N:P ratios were consistently lower in female flies compared with co nspecific males suggesting phosphorus demands during oogenesis are high. 5. Potential mechanisms by which Drosophila deal with N or P limitation in nature are discussed.