I happened to check pollination aspects in Nervilia. Few species are supposed to be self pollinated while some are pollinated by wasps and small bees. Some species offer nectar for pollinators where as those which lack nectar attract pollinators by false methods like deception.
Reference: Dressler, R. L. 1993. Phylogeny and classification of the Orchid family. Cambridge University Press, Cambridge. I dont have access to another important book on pollination aspect: An atlas of orchid pollination: America, Africa, Asia and Australia By Nelis A. Cingel. If anyone has this reference then please check page 132 and let me know.... Regards Pankaj
