Abstract: Medicago sativa is a kind of typical allogamic plants, and mainly depends on the pollinators such as bees for its seed production. In this paper, the pollinating insect species and their foraging behaviors on M. sativa at the Zhangye station of Hexi Corridor were investigated. There were 22 pollinating insec species belonging to 4 orders and 11 families, among which, native bee species Megachile abluta, M. spissula, Xylocopa valga, Andrena parvula and Anthophora melanognatha were the main pollinators. M. abluta, M. spissula and X. valga were of unipeak type with diurnal foraging activities trom 11:30 to 15:30, while A. parvulaand A. melanognatha were of double-peak type with diurnal foraging activities on 9:30-11:30 and 16:30-18:30, indicating a complementary relationship among the pollinators. The main pollinators had significant differences in their tripping frequency and landing time, and their foraging behaviors were correlated with their body sizes.

Key words: Ecosystem health, Evaluation index, Agroecosystem