Worker policing in the honeybee

Abstract

IN most species of social Hymenoptera with queen–worker dimorphism, workers cannot mate but retain functional ovaries¹; because males arise from unfertilized haploid eggs, workers can potentially produce males. Worker-derived males are frequent in some species, but in others occur only in queenless colonies^2,3. Workers are more related to their own sons (coefficient of 0.5) than to the queen's sons (their brothers; 0.25); they are also more related to nephews (0.375) than brothers if queens mate with one male, but if queens mate with more than two unrelated males a worker's mean rela tedness to nephews is less than to brothers^3–5. In this case workers could benefit by 'worker policing'^3,5: prevent-ing each other from producing males, perhaps by destroying worker-laid eggs or by aggression toward reproductive workers. Worker reproduction is rare in queenright colonies of species with multiply mated queens (such as honeybees⁶ and some yellowjacket wasps⁷), but is common in some monandrous species (bumblebees and stingless bees³). Here we describe experiments showing strong discrimination by honeybee (Apis mellifera) workers against worker-laid male eggs, supporting the worker-policing hypothesis. The honeybee was studied because queens mate with 10–20 males⁸, making worker policing seem likely as a cause for the rarity of worker-derived males (about one in a thousand males is worker-derived⁶).