FORAGING AND COURTSHIP BEHAVIOR 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 examine d in the solitary bee Anthophora plumipes (Hymenoptera: Anthophoridae) , which shows resource-based polygyny at floral food sources in Britai n in spring. 2. Larger males are able to fly at lower temperatures tha n smaller males, and can therefore court females under conditions in w hich smaller males cannot fly. This is predicted from patterns of endo thermic ability at low temperatures already demonstrated within this s pecies. 3. Video analysis of male competition for opportunities to ini tiate courtship with tethered females showed that larger males are als o competitively superior, and can displace smaller males from favoured flight positions immediately behind females. 4. The mating system sho wn by male A.plumipes is strongly dependent on male density. At low de nsities, males show exclusive territoriality at floral sources. As mal e density increases, this strategy is abandoned in favour of patrollin g with considerable spatial overlap between males, and opportunistic p olygyny.5. Despite high endothermic abilities, male behaviour is highl y dependent on weather, and particularly ambient temperature. Males ba sk in the early morning and maintain high thoracic temperatures. Tempe rature data from freshly killed bees show that thoracic warming from s olar sources effectively doubles the thermogenic power generated by th e bee alone at low ambient temperatures. 6. Male strategies in A.plumi pes are compared to female responses to climate. Having controlled for differences in body size there is no difference in endothermic abilit ies 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 succ ess on flight activity for the two sexes.