Abstract: Results are presented for a study on the early occurance and age composition of medical important flies in Yuncheng city cf Shanxi province during Nov. 1986 and May 1987. 21 species and 8445 flies (females 6601) were captured in the early spring. The female/male ratio was 3.6. The predominant species were Aldriohina grahami,Lucilia sericata and Muscina stabulans etc. 225 females were anatomized, of which, 84% were un-oviposited, 40% were pregnant. Follicular stages were mostly from Ⅱ to Ⅴ Detinovas stages. These adults were frequently active in fish markets and warmer places. The earliest adults appeared in early Feb. Their occurance was related to the changs of air temperature. Early larvae appeared in the middle of March, breeding in animal wastes. Suggestions were given for the control of flies in the early seasons.

Key words: Brachydanio rerio, Embryo development, Toxicity evaluation