A photographic account of pollen digestion by adult hoverflies

The method of pollen digestion by adults of the hoverfly Cheilosia albitarsis Mg. (Diptera: Syrphidae) was investigated by observing pollen grains at different stages in their progression along the gut. No form of mechanical ‘grinding’ to break up the grains was observed, as suggested by some previous authors. Instead, there was an exudation of the pollen grain contents through one of the pores in the pollen exine. This exudation may start as a growing pollen tube. The exact conditions which cause the pollen grains to give up their contents in this way are unknown, but it is suggested that nectar sugar within the gut may provide the necessary stimulus.