Some observations on the pollination of round-leaf orchid, Galearis (Amerorchis) rotundifolia, near Jasper, Alberta

Abstract

On June 16 and 17, 2010, data were collected on pollination in a population of Galearis rotundifolia at the confluence of the Maligne and Athabasca Rivers north of Jasper, Alberta. The primary pollinator was the bee Osmia proxima and this species was also the most frequent visitor. While most flies were visitors, four species, Eriozona (Megasyrphus) laxus, Eristalis (Eoseristalis) hirta, Eristalis (Eoseristalis) rupium, and Eupeodes (Lapposyrphus) lapponicus also served as pollinators. It is estimated that 25-44% or more of flowers were pollinated in the previous year, a relatively high percentage that supports the "advertisement model" for evolution of food deception in orchids. The pollinating bee or fly lands on the lip and probes the spur which is approximately the same length or longer than the tongue. In the process of pushing into the flower and backing out, the sticky contents of a bursicle are either discharged by the backward movement of a flap or by forward pressure. Either of these actions may release adhesive fluid which fixes the viscidia onto the front of the insect's head. The gradual bending forward of the caudicles reduces likelihood of pollination of consecutively visited flowers with pollen from those recently visited flowers on the same plant (geitonogamous pollination) and thus promotes outcrossing.