Pollination of seven zingiberaceous and two gesneriaceous species was studied in natural forests at various altitudes in West Sumatra, Indonesia. Terrestrial, red, long-tubed flowers of Achasma macrocheilos were visited by a large, remarkably long-tongued anthophorine bee, Amegilla elephas. The swiftly-flying bees showed traplining foraging behavior just like euglossine bees in the Neotropics. This bee species was oligolectic to the plant species and almost the only pollinator of it. Yellow (rarely white), long-tubed flowers of Zingiber puberulum, Grobba aurantiaca, Amomum aculeatum and Cyrtandra pendula were pollinated by median-sized, shade-loving, traplining, long-tongued anthophorine bees in the genera Amegilla and Elaphropoda. White, short-tubed flowers of Amomum uliginosum and Cyrtandra aff. grandiflora were pollinated by traplining halictid bees in the genus Nomia. Long-tubed flowers borne on red stout spikes of Hornstedtia aff. conica and Phaeomeriafulgens were pollinated by a long-billed sunbird, Arachnothera longirostra. These ornithophilous flowers produced significantly more nectar of lower sugar concentration than the melittophilous flowers.
According to the proboscis lengths, long-tongued bees were classified into three groups, which corresponded to the three pollination guilds of the melittophilous flowers. Among species in a bee guild, convergence of proboscis lengths was detected, and the floral hosts of the bee species were sometimes overlapping. Twenty-five percent of melittophilous species were visited by more than one bee species, but nonetheless most individual plants were visited by only a single bee species. At higher altitudes more than 1400 m, anthophorine bees were displaced by bumblebees and the guild structure of longtongued bees was simpler than at lower altitudes.