Worker Policing in Social Hymenoptera

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Colonies of social ants, bees, and wasps provide fascinating examples of cooperation in the animal world. However, modern evolutionary theory suggests that there should be considerable conflict over reproduction within an insect colony. In particular, there should be conflict between individual workers and the queen over male production. (Worker ants, bees, and wasps are females. In most species, workers cannot mate but can lay unfertilized eggs, which develop into males.) Theory suggests that individual workers should prefer to rear their own sons rather than their brothers, the sons of the queen, because they are more genetically related to sons than brothers. In some species of social insects, for example, bumble bees, workers produce many of the colony's males, whereas in others, for example, honey bees and yellowjacket wasps, all the males are sons of the queen. The absence of male honey bees produced by workers is thought to result from workers preventing each other from reproducing by eating each other's eggs. This "worker policing" has apparently evolved in the honey bee because the queen mates with many males. This leads to workers being more genetically related to the queen's sons than to the sons of other workers (who are mostly half-sisters), so that it is in each worker's genetic interest to stop other workers from reproducing. In contrast, bumble-bee queens mate with only one male, so that workers are more related to the sons of the workers (who are all full sisters) than to the queen's sons, and should not stop each other from reproducing. This research project will examine in more detail the mechanism of worker policing in honey bees, and also look at yellowjacket wasps to see if worker policing by differential egg removal occurs in these insects as well. One important area of research will investigate how worker honey bees can distinguish queen- from worker-laid male eggs, by looking for a queen-produced chemical (pheromone) that may give their eggs a distinctive odor. In addition, the project will quantify the rate of production of worker-laid eggs in normal bee hives, and will look at the behavior of worker bees entering cells containing male eggs to see if some workers are special "police bees."