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Annual monitoring of the population dynamics of the oriental fruit fly Bactrocera dorsalis(Hendel)(Diptera:Tephritidae)in Xishuangbanna,southe Yunnan,was conducted by using methyl eugenol-baited traps in 1997,2000,and 2003,and factors including temperature,rainfall,and host species with respect to the population fluctuation were analyzed systematically.The results showed that the fruit fly was present all year round in Xishuangbanna.Its population remained at a lower level from November to February,and increased from March until it reached a peak in June or July,depending on the rainfall that year.Afterward,the fly population declined remarkably until October.Temperature,rainfall,and host fruits were major factors comprehensively influencing the population fluctuation.The monthly mean temperature was in a range of temperatures suitable for development and reproduction of the fly.But the monthly mean minimum temperature from December to February was lower than the suitable temperature range,which was suggested a possible reason for the lower populations in winter months.Rainfall was another essential factor influencing the population fluctuations.The population was depressed when the monthly rainfall amount was lower than 50 mm,but increased when rainfall ranged from 100 mm to 200 mm.When the monthly rainfall amount was higher than 250 mm,the fruit fly population was reduced remarkably.The heavy rain in July and August explained the decreasing population.Mango,orange,pear,longan,and peach were found to be the main host species of the fly in Xishuangbanna.Among them,mango and longan were most preferred by the fly.Therefore,the planted areas,fruiting period,and production exerted essential effects on the fly population fluctuations,which were regarded as another major factor influencing the fly population in that area.Briefly,temperature,monthly rainfall,and the host species,through the way of their functions,the influence strength,as well as the period that they occurred comprehensively impacted the population fluctuations of the fruit fly in Xishuangbanna.