Queenless colonies of the Asian red dwarf honey bee (Apis florea) are infiltrated by workers from other queenless colonies

In all honey bee species studied thus far, 2-4% of the workers were not born in the sampled colony. These unrelated (nonnatal) workers are thought to arise via orientation errors while returning from foraging trips. Interestingly, in colonies of the red dwarf honey bee, Apis florea, the proportion of nonnatal workers increases significantly when the colonies become queenless, and these workers are more likely to have active ovaries and lay eggs than natal workers. As a result, queenless colonies are heavily parasitized with the eggs of nonnatal workers, but the origin of the parasitizing workers is currently unknown. Here we show that workers from queenless A. florea colonies are far more likely to leave their colony and join another colony compared with workers from queenright colonies. Choice experiments showed that these drifted workers are much more likely to join a queenless colony than a colony with a queen. Perhaps surprisingly, not many workers from queenright colonies joined queenless colonies despite the opportunity for direct reproduction in queenless colonies. We suggest that the inclusive fitness benefits of remaining in the natal colony in the presence of the queen exceed the benefits of direct reproduction in an unrelated queenless colony.