Heriades truncorum (Megachilidae) is a specialist bee that forages on Asteraceae and collects pollen by tapping its abdomen on pollen-presenting florets which places the grains directly in the ventral scopa. We tracked pollen transfer by female H . truncorum between conspecific inflorescences of Inula ensifolia and Pulicaria dysenterica by labelling pollen with quantum dots. On average, bees transferred 31.14 (I . ensifolia ) and 9.96 (P. dysenterica ) pollen grains from the last visited inflorescence, 39% and 45% of which were placed on receptive styles. Pollen germination ratio is significantly lower for inflorescences of P. dysenterica visited by one H . truncorum (0.13%) compared with open control inflorescences (0.51%), which suggests that the bees mainly transfer self-pollen of these self-incompatible plants. Thus, a single visit by H . truncorum does not grant the plant high reproductive success, but the bees' abundance and flower constancy might reduce this disadvantage.Asteraceae / oligolecty / plant-pollinator interaction / pollen germination rate / single-visit deposition
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