In Xishuangbanna tropical region，an undescribed species of gall midge on Ficus benjamina lays its eggs in the ovary of female flowers，producing a large gall in which the larva feeds on the gall’s tissue to complete its life cycle． We investigated the occurrence of gall midge onF． benjamina through systematic sampling at a fixed time and location in2010. Eighteen crops were sampled and gall midges found to occur in 17 of them． The percentage of figs attacked by gall midges was over 60% in 13 of the crops，reaching as high as 100%． Gall midges parasitized only up to 6% of femaleflowers and on average produced fewer than forty individuals in a single fig． The occurrence of gall midges reduced the number of seeds produced and had a deadly effect on the reproductionof pollinators． We observed the behaviour of eclosion，mating and flight of the gall midge． We found that all gall midges colonizing a single fig took 5—7 days to complete eclosion，and that the eclosion peak appeared in the 2 ^{nd —3rd． In one day，eclosion peaks occured at 8:00— day}

10:00 in the morning and 8:00—12:00 at night． The peak of activity after eclosion was at 8:00—11:00 in the morning．Male gall midges emerged first and assisted female gall midges to emerge． Once a female had emerged，a male would matewith her． Female gall midges left the natal fig trees after mating to search for appropriate trees for egg-laying． However， after mating，male gall midges died under the natal trees． Our results provide a basis for future study of the technology ofgall midge control． Key words gall midge，occupancy，biological characteristics，pollinating fig wasp，Ficus benjamina