MSc Student (Adv. Harald Krenn)

Unit for Integrative Zoology, Department of Evolutionary Biology
University of Vienna

Abstract

The labiomaxillary complex of Vespinae evolved to efficiently forage various solid and liquid foods, such as animal proteins, carbohydrate rich fluids and water as well as woody fibres for nest construction. Before liquids are swallowed and transported into the crop, particles are filtered out. This study examines the morphology and function of the mouthparts and alimentary tract, focussing on this filtration process. The feeding organs, preoral cavity and prepharynx, are studied using µ-CT, 3D reconstructions of semithin sections, SEM and feeding experiments with glass beads in workers of Vespula germanica. To test for filtration, barium sulfate has been used as a fluid contrast agent, a method rarely used in entomology. The results indicate that particles bigger than 212 µm are filtered by the mouthparts. The prepharynx bears interlinked microtrichia arranged in rows oriented towards the infrabuccal pocket. Together with the cuticle structures of the epi-, and hypopharynx, this enables an additional filtration of particles bigger than ~ 100 µm. This could be the maximum size of particles, which are able to safely pass the narrow wasp waist. For the first time a detailed illustration of the multi-layered filtration system formed by the mouthparts and the preoral cavity and its function is presented.