Seasonal nest usurpation of European colonies by African swarms in Arizona, USA

Nest usurpation is a form of reproductive parasitism that may contribute to the ability of African bees to displace European honey bees in the Americas. We examined nest usurpation by African swarms over a two-year period in a southern-Arizona apiary that contained 76 five-frame European colonies. We observed a mean annual usurpation rate of 21%, with strong seasonal trends in usurpation activity. Most usurpation:, occurred from October-December, with a minor peak of usurpation activity in the spring-summer months. The seasonal patterns of usurpation corresponded with the reproductive swarming season in spring and summer and the absconding season in the fall-winter months. Queenless colonies, colonies that contained a queen confined in a cage, and those that had been recently re-queened were 2-8 times more likely to be invaded than were colonies that contained an actively laying queen, suggesting that queen condition may have a major influence on host-colony susceptibility to usurpation. This trend was particularly pronounced in October-December, during which months the usurpation rates experienced by caged-queen and queenless colonies approached 20-50%. Our results show that nest usurpation is seasonally frequent among honey bees in the southwestern U.S., which suggests that reproductive parasitism contributes to the invasion success of African honey bees and possibly other introduced social insect species.