Adaptations for fungal grazing in Lauxaniid flies

Summary

An examination of the mouth parts and gut contents of 40 species of adult lauxaniid flies from Panama and from England indicates that the majority of forest-dwelling species feed upon fungal hyphae and spores. The ventral face of the labellum is equipped with various devices for cutting and raking in lengths of fungal hyphae. These are of two types: sclerotized ‘prongs’ and shallow ‘scoops’ with serrated edges. Not only are the pseudotracheae wide but they are few in number and their apertures are large enough to permit the entry of sizeable pieces of fungal hyphae. These have been demonstrated lying within the pseudotracheal canals. These adaptations enable the flies to feed upon solid particles while the labellum is spread out flat. This differs from the generally accepted view of the feeding habits of cyclorrhaphous flies. A structure termed the ‘beak’ seen in most of these fungivorous species, which is the prolongation of the anterior tip of the labial gutter, and which is exposed along with minute prestomal teeth, when the labial lobes are folded back, might function in the dislodging of fungal material from crevices. Three species from Panama had none of these adaptations, neither did they have any fungal material in the gut, so it is assumed that they are liquid feeders.