The scientists from the University of Washington and the Smithsonian Tropical Research Institute say the tiny fly helps determine which bees become queens and which become workers. They said their finding marks the first documented example of a parasite having a positive affect on the social behavior of its host.
The researchers said the action is accomplished by fly larvae stealing food from developing immature bees. The researchers found resulting smaller bees are more likely to stay and act as helping workers, while larger bees tend to depart and start new nests as egg-laying queens.
"We often think of parasitism in terms of it affecting an animal's fitness, its survival or its ability to reproduce," said UW Associate Professor Sean O'Donnell. "This study is a counterintuitive take on parasitic infection. It encourages us to look for complicated ecological relationships between different species.
"Parasitism may encourage sociality in some situations," he added. "Here it is promoting social behavior."
The research that included Adam Smith and William Wcislo appears in the Journal of Insect Behavior.