A small parasitic fly, Apocephalus borealis, may turn out to be one player in the failing health of honey bee colonies in North America. The parasite, a type of phorid fly, has long been known to parasitize bumble bees and paper wasps, but recent research shows that it may also attack honey bees.
In an article published yesterday in the journal PLoSOne, researchers explain that the tiny adult female fly lands on a honey bee abdomen and lays eggs by placing her ovipositor into the bee. The entire process takes two to four seconds. Seven days later the adult phorid larvae emerge from the area between the bee’s head and thorax. One to thirteen larvae emerge and leave the dead bee behind. The larvae then pupate elsewhere.
Oddly, honey bees parasitized by the phorid flies are attracted to light. Individuals are found to abandon their hives at night and fly toward sources of light where they remain until they die. In fact, it was large numbers of dead honey bees around lights on the campus at San Francisco State University that lead to the discovery of phorid fly activity in honey bees. Also of interest is the fact that many of the phorid flies were found to test positive for Nosema ceranae and deformed wing virus—pathogens often associated with dead colonies.
The authors of the paper speculate that the native phorid fly has recently evolved to accept the non-native honey bee as a host. If the fly had long been a parasite of honey bees, adult phorid flies, their larvae, or accumulations of dead bees around lights would have been noticed before now. As they point out, the honey bee is one of the most studied creatures on earth so it is doubtful this fly would have escaped detection.
If the fly has indeed shifted hosts, it is bad news for beekeepers. Unlike bumble bees and paper wasps—creatures without huge populations—a honey bee colony can provide a vast breeding ground for the flies. And at one to thirteen larvae per bee, it wouldn’t take long for the flies to overwhelm a colony. Furthermore, this tremendous population of flies could leave the hive and harm bumble bees and perhaps other wild bees as well. Scary stuff, great material for horror flicks.
I urge you to click on the link to the original article and enlarge the photo of a phorid larva leaving a bee. For more details on this phorid fly, see Zombee Questions and Answers.