The pollination of Pedicularis palustris by nectar thieves (shorttongued bumblebees)

Operation of the pollination mechanisms of Pedicularis palustris L. by nectar and pollen foraging bumblebees ( Bombus Latr.) was studied. It was found that pollination could be achieved in two ways: 1. by normal collectors, viz. long-tongued bumblebees; 2. by nectar thieves, viz. short-tongued bumblebees. Normal collectors (Bombus muscorum L., B. pascuorum floralis Gmel. and B. hortorum L.) introduced their head and tongue into the 12 mm corolla tube to secure nectar, while stigma and style swept the forager’s head and thorax. Nectar thieves (Bombus jonellus Kirby, B. terrestris L. and B. lucorum L.) obtained nectar through holes in the corolla tube made by the latter two species. Pollen collecting thieves pushed against the upper lip while hovering in the air. Thus pollen was released and dusted on venter and legs. This foraging behaviour was attended by a hissing sound, presumably caused by wing vibrations. Both ways of pollination resulted in large-scale seed-setting, thus contradicting the common interpretation that nectar thieves do not effect pollination and seed production.