Social wasps perform a variety of tasks with their mouthparts. Female workers use them to feed on carbohydrate-rich fluids, to build nests by collecting wood fibers and forming paper, to hunt and manipulate insect prey for feeding larvae as well as for brood care. Since male wasps neither feed on insects nor participate in nest building, sex-specific differences in mouthpart morphology are expected. Despite these different applications, general mouthpart morphology of male and female wasps from the genus Vespula was similar. However, males possessed significantly shorter mandibles with fewer teeth than females. Furthermore, the adductor muscles of the mandibles were distinctly smaller in males than in females. Male wasps showed a higher number of sensilla on the mandibles and the labial palpi. Mouthpart dimorphism and functional morphology of fluid uptake are discussed.
The mouthparts of Vespidae have evolved to forage various solid and liquid foods, such as animal prey, carbohydrate-rich fluids, as well as woody fibres for nest construction. Before nutritional fluids are ingested into the crop, bigger particles need to be filtered out. This study examined the functional morphology of the mouthparts, the preoral cavity, and the proximal alimentary tract inside the head focusing on this filtration process. The feeding organs and preoral cavity were studied using µCT and SEM that were complimented by feeding experiments with glass beads in workers of Vespula germanica. To visualize fluid ingestion into the head and alimentary tract, barium sulfate solution was used as contrast agent; a method that is rarely applied in entomology. Experimental results indicate that large glass beads (>212 µm) were filtered by the mouthpart structures before entering the preoral cavity. Smaller glass beads (152–212 µm) were found inside the infrabuccal pocket in front of the mouth. Morphological evidence indicates that cuticle structures of the epipharynx, hypopharynx, and cibarium filter this particle size inside the preoral cavity while glass beads < 152 µm reach the crop. A double fluid filtration system is proposed that is formed by (1) bristles of the mouthparts and (2) microtrichia of the preoral cavity.
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