OPTIMAL TIMING OF THE PRODUCTION OF SEXUALS IN BUMBLEBEE COLONIES

Colonies of annual eusocial insects often produce only workers until t hey switch to the production of sexuals (queens and males). This switc h from the ergonomic phase to the reproductive phase has been modelled by Macevicz & Oster (1976). Their model predicts that the production of sexuals should take place approximately one generation tone brood d evelopmental period) before resources are depleted in order to maximis e the number of sexuals. Bumblebees, however, produce sexuals early (r elative to colony lifetime) when resources are still abundant and thus the model of Macevicz & Oster does not hold for these insects. Here w e show that Macevicz & Oster's prediction hinges critically on their a ssumption that the egg laying rate of the queen is a function of the f oraging effort of the workers. This assumption does not hold for bumbl ebees, where queens lay eggs at a constant rate. Taking this feature o f bumblebees into account the model predicts early production of sexua ls, since it does not pay to produce more workers and collect more res ources than needed to raise sexuals.