Plant-robber-pollinator interactions are studied in an alpine plant, Salvia przewalskii, that is pollinated by long-tongued Bombus religiosus and short-tongued B. friseanus, and robbed by B. friseanus.
Ye et al. find that neither fruit set nor seed set were significantly affected by nectar robbing, and furthermore that nectar replenishment does not differ between flowers that are robbed or legitimately visited. Concluding that nectar robbing has no adverse effect on female reproductive success, the authors propose that nectar replenishment could serve as a defence mechanism to protect against the possibility of nectar robbing, enhancing reproductive fitness and ensuring that bumble bee pollinators persist in visiting nectar-robbed flowers.
Ye, Z.-M., Jin, X.-F., Wang, Q.-F., Yang, C.-F., & Inouye, D. W. (2017). Nectar replenishment maintains the neutral effects of nectar robbing on female reproductive success of Salvia przewalskii (Lamiaceae), a plant pollinated and robbed by bumble bees. Annals of Botany. https://doi.org/10.1093/aob/mcw285