Abstract: In the study,an all year round monitoring through lure-traps in 1997,2000 and 2003 was conducted on the population dynamics of oriental fruit fly,Bactrocera dorsalis (Diptera:Tephritidae) in Xishuangbanna of Southern Yunnan,and the factors in relation with its population fluctuation,including temperature,rainfall,and host species were analyzed.The fruit fly occurred year-round in Xishuangbanna,with a low population level from November to February,and increased steadily from March to July or August.An increasing peak appeared in July or August,depending on the rainfall amount in that year.Afterwards,the fly population declined markedly until to October.Temperature,rainfall,and host fruits were supposed to be the major factors affecting the population fluctuation.The monthly average temperature in Xishuangbanna was in the ranges suitable for the development and reproduction of the fly,but the monthly average minimum temperature from December to February appeared to be lower than the suitable temperature,which was suggested to be responsible for the low populations in the winter months.Rainfall was another essential factor affecting population fluctuation.The population was depressed when the monthly rainfall amount was lower than 50 mm,but increased when the amount ranged between 100 and 200 mm.Under conditions the monthly rainfall amount was higher than 250 mm,the fruit fly population was reduced markedly,which explained the decreasing population in July or August when the heavy rain occurred.Mango,orange,pear,longan,and peach were the main host species of the fly,among which,mango and longan were most preferred by the fly.Therefore,their planted area,fruiting period and productivity exerted essential effects on the fly population fluctuation,and regarded as another major factor affecting the fly population in this area.

Key words: Bactrocera dorsalis, Population dynamics, Xishuangbanna