The evolution of worker sterility in honeybees: the genetic basis of failure of worker policing

Benjamin P Oldroyd, Katherine E Osborne

Abstract

Worker honeybees (Apis mellifera) usually only lay eggs when their colony is queenless. However, an extremely rare ‘anarchistic’ phenotype occurs, in which workers develop functional ovaries and lay large numbers of haploid eggs which develop into adult drones despite the presence of the queen. Studies of such colonies can give important insights into the mechanisms by which worker sterility is maintained in normal colonies. Here we report on the results of a breeding programme which enhanced the frequency of the anarchistic phenotype. Colonies derived from queens inseminated only by worker–laid males showed up to 9% of workers with highly developed ovaries. In these colonies a large proportion of males arose from worker–laid eggs. Colonies headed by queens inseminated with 50% worker–laid drones and 50% queen–laid drones showed variable phenotypes. In most such colonies there was no worker reproduction. In some, many workers had highly developed ovaries, but no worker–laid eggs were reared. In one colony, many worker–laid eggs were reared to maturity. The results suggest that the anarchy phenotype results from a complex interaction of queen genotype, the worker genotype of subfamilies that successfully reproduce and of those that do not, and the external environment.