Pollenivory in larval and adult flower flies: pollen availability and visitation rate by Toxomerus politus SAY (Diptera: Syrphidae) on sorghum Sorghum bicolor (L.) MOENCH (Poaceae) (Pollenverzehr bei Schwebfliegenlarven und -imagines: Pollenverfügbarkeit und Besuchshäufigkeit vonToxomerus politus SAY (Diptera: Syrphidae) bei der Mohrenhirse Sorghum bicolor (L.) MOENCH (Poaceae))

The larvae and adults of both sexes of Toxomerus politus SAY, 1823, were observed visiting the flowers of Sorghum bicolor (L.) MOENCH (Poaceae) in Brazil, where female flies were also seen ovipositing. The relationship between sorghum pollen availability and the visitation rates was examined, as well as the diurnal changes in the sex ratio of adult flies visiting the flowers. The feeding behaviours of adults and larvae were also studied. Highest visitation rates occurred early in the morning, before 09:00, when pollen was adhering to the anthers and relatively small amounts of pollen were in the air. The adult sex ratio for visitation rates indicates that more females than males visit the flowers. This suggests that females need more pollen than do males, as a protein source to develop their reproductive organs and eggs. The larvae of T. politus were also found to feed on sorghum pollen, and records of pollen-feeding syrphid larvae are exceptionally rare. The larvae of other Toxomerus species are insectivorous. It seems from these results that T. politus uses the pollen of at least some Poaceae for its entire life cycle.