Abstract: Pollination structure and behavior of fig wasps, and the pollen-ovule (P/O) ratio of their host figs are all important indicators of their pollination mode. Field observation was made on Ficus annulata from August 2010 to June 2011 in Xishuangbanna, Yunnan, southwestern China and the pollination structures of Deilagaon annulatae, the pollinator of F. annulata, were examined through Scanning Electron Microscopes (SEM). The results showed that two pollen pockets disappeared and pollen grains can adhere to the bristles in peristaethium, which are all characteristics of a passive mode. No active pollen collecting behavior was observed under microscope, suggesting that the existing coxal combs have lost the function of actively collecting the pollen. Meanwhile, F. annulata is a typical passive pollinated species with a large number of male flowers in each syconium; the P/O ratio is high; and the pollen grains spread when the mature anthers split automatically. Given evidences from both sides, we deduce that the pollination mode of this system is passive. D. annulatae is the only fig wasp species reported with yellow body color in Xishuangbanna. They prefer emerging and acting at night when the temperature is low. During the receptive phase, Lipothymus sp. is the only non-pollinator that enters the fruit to lay eggs there along with the pollinator, and with much higher abundance. In a syconium, the number of wasp offspring is significantly greater than that of the seeds, showing a rare fig-wasp mutualism system in which fig wasps act as the dominator.

Key words: Deilagaon annulatae, Ficus annulata, pollination, pollination structure, pollination behavior, emergence time