Comparative study of the population reproductivity of three fruit flies melon fruit flyBactrpcera cucurbotae, oriental fruit fly B,dorsalis and pumpking fruit fly B. tau under differentphotoperiods(L:D= 16 :8～8:16)with constant temperature(25℃)and fluctuating relativehumidity(75%～95%)and under cyclical fluctuating temperatures , relative humidity and stablephotoperiods(20～25℃,L:D=4: 10,RH75%～95%125～32℃,75%～95%,L:D=10:14)were conducted.The results showed that middle and long photoperiods were favorable to the reproduction ofthree fruit flies.Short photoperionds were less favorable, By compared the population parame-ters,either under the circumstances of various photoperifor with constant temperature and fluctu-ating relative humidity or under cyclical fluetuating temperatures and relative humidity with con-stant photoperiod , all of three fruit flies had longer ovipositional period,large numbers of eggand overlapping generation. In the cyclical fluctuating condition of 20～25℃,50% Σlxm_x ofB. tau and B. dorsalis was distributed within 60 days after adult emergence, but 50% Σl_xm_x of B. cucurbitae was 130days;in 25～32℃,50%Σl_xm_x of B. tau and B. dorsalis was 40 days,B.cucurbitae’s was 70 days. The population density increase of both B. tau and B. dorsalis was morequiker than that of B. cucurbitae,B. dorsalis and B. tau are recognizied as more typical r-repro-ductive strategy than B. cucurbitae does.