Flowering, pollen production and insect visitation in two Aconitum species (Ranunculaceae)

Flowering phenology, diurnal dynamics of blooming, insect visitation and pollen production in Aconitum lycoctonum L. and Aconitum carmichaelii Debeaux were investigated in 2012–2013 in the Lublin area, SE Poland. Flowering of A. lycoctonum occurred in June/July, whereas A. carmichaelii bloomed in September/October. Both Aconitum species differed in terms of the diurnal pattern of flowering. The flowers of A. lycoctonum started opening at 5.00, whereas those of A. carmichaelii started blooming at 8.00 (GMT+2h). The species differed in the number of anthers per flower, the size of anthers, and the mass of pollen produced in anthers. As a result, the flowers of A. lycoctonum produced less pollen (mean = 1.0 mg per 10 flowers) than the flowers of A. carmichaelii (mean = 8.2 mg per 10 flowers). The estimated pollen yield was 0.2 g per m2 for A. lycoctonum and 1.6 g per m2 for A. carmichaelii. The flowers of both Aconitum species were foraged exclusively by bumblebees with the predominance of the long-tongued Bombus hortorum. Nectar was a more attractive floral reward than pollen. The propagation of Aconitum lycoctonum and A. carmichaelii in ornamental gardens may support the conservation of bumblebees whose populations are steadily declining