Foraging and courtship behaviour in males of the solitary bee Anthophora plumipes (Hymenoptera: Anthophoridae): thermal physiology and the roles of body size

.1 The effects of climate and body size on male behaviour were examined in the solitary bee Anthophora plumipes (Hymenoptera: Anthophoridae), which shows resource‐based polygyny at floral food sources in Britain in spring. 2 Larger males are able to fly at lower temperatures than smaller males, and can therefore court females under conditions in which smaller males cannot fly. This is predicted from patterns of endothermic ability at low temperatures already demonstrated within this species. 3 Video analysis of male competition for opportunities to initiate courtship with tethered females showed that larger males are also competitively superior, and can displace smaller males from favoured flight positions immediately behind females. 4 The mating system shown by male A plumipes is strongly dependent on male density. At low densities, males show exclusive territoriality at floral sources. As male density increases, this strategy is abandoned in favour of patrolling with considerable spatial overlap between males, and opportunistic Polygyny. 5 Despite high endothermic abilities, male behaviour is highly dependent on weather, and particularly ambient temperature. Males bask in the early morning and maintain high thoracic temperatures. Temperature data from freshly killed bees show that thoracic warming from solar sources effectively doubles the thermogenic power generated by the bee alone at low ambient temperatures. 6 Male strategies in A.plumipes are compared to female responses to climate. Having controlled for differences in body size there is no difference in endothermic abilities between the sexes. Males do not, however, fly under conditions in which females of the same size would remain active. These results are discussed in the light of differential dependence of reproductive success on flight activity for the two sexes.