AbstractMutualism is a relationship between individuals of different species that benefits all the partners. However, this interaction may also be described as mutual exploitation. The “host sanctions effect” predicts that the hosts punish partners that cheat by receiving benefits without paying for them. Fig trees (Ficus) and their fig-pollinating wasps (Agaonidae) constitute a mutualistic system with a mainly one-to-one relationship. In order to test if there exists the “host sanctions effect”, we carried out a study at Xishuangbanna Tropical Botanical Garden, Yunnan Province on the monoecious fig tree Ficus benjamina, which is actively pollinated by Eupristina koningsbergeri. We produced two groups of pollinating wasps, either carrying pollen or not, and introduced one or two foundress wasps from each group into single figs. Figs entered by no wasps aborted rapidly, but almost all figs entered by wasps completed their development normally, except a few entered by a single pollen-free wasp. However, pollen-loaded foundresses produced significantly larger broods than foundresses without pollen. This effect was particularly marked in figs containing two foundresses. Our results show that active pollination is not essential for the reproduction of the pollinator, but does improve its reproductive success. This suggests that a sanctions effect is operating.