Bumblebee-mediated pollination of English populations of the Military Orchid (Orchis militaris): its possible relevance to functional morphology, life history and climate change

Abstract Opportunistic observations of the longest-standing British population of Orchis militaris L. suggest that bumblebees (Bombus spp.) may have become the primary pollinators of the orchid at the site. We document pollination by (female) workers of B. pratorum and males of the brood parasite B. vestalis. Placement of the pollinaria on the bodies of the bees varied greatly, presumably reducing the bees’ efficiency as pollinators due to (a) delayed contact of pollinaria with stigma (increasing the frequency of geitonogamy), (b) failure to contact any stigma due to misplacement, or (c) failure to contact any stigma due to rapid removal of the pollinaria by the bee. However, suboptimal pollinarium placement may be compensated for by the comparative determination shown by the bees in exploring both flowers and inflorescences. Recent environmental change has reduced bumblebee diversity in Europe, survival favouring species with short tongues that correspond in length with the (non-rewarding) labellar spur of O. militaris. We conclude that models of pollination ecology should consider the caste and life history of the relevant insect and, given the involvement of a brood parasite in the present study, should extend beyond the immediate plant and pollinator to consider other elements of the relevant ecosystems.