|Figure 2 from Core et al 2012|
Professor John Hafernik and his team found the larvae of this fly inside up to 10-15% of foraging worker bees in autumn. The fly larvae kill workers in about 7 days.Flies were found in samples from migratory bee colonies that travel over much of the US 48 states, so the problem is not restricted to California. Indeed moving the colonies may spread the fly.
Panel B shows the adult fly landing briefly on a bee and laying eggs - a process that takes only a few seconds. This seems to happen while the workers are collecting nectar and pollen.
After about a week, the 3-20 larvae feeding inside the worker have grown large. At this point infected workers abandon the hive, often at night, and fly away. They are attracted to lights where they seem disoriented and uncoordinated. Normal bees almost never fly at night. Up to 91% of the workers found at lights at night were infected with the flies.
Typically the next day the bee dies and some time later fly larvae crawl out of the bee (panel C) to pupate in the soil and later emerge as adults.
Hive abandonment is part of Colony Collapse Disorder, and this fly may be contributing to that syndrome. The researchers found that the adult flies may be carriers of several honeybee diseases, so may spread them from one hive to the next.
Although these flies are a native part of the large suite of parasites, parasitoids, and diseases which attack our native bumblebees, they pose a disturbing new threat to bumblbees. Why? Bumblebee colonies are much smaller than honeybee hives and are very small in spring and early summer, so the fly's native hosts are not as abundant. Flies may build up to much larger numbers by feeding on very numerous honeybees. The researchers showed the flies attack bumblebees and honeybees indiscriminately, so populations of native bumblebees may be diminished as an unintended consequence of keeping honeybees.
A further risk is that honeybees and to a smaller extent bumblebees are shipped between continents. If infected North American worker bees end up in regions where the fly is not native, damage could spread.
Because infected bees are uncoordinated, clumsy, and go out at night they have been dubbed "zombie bees". This may give some zombie movie fans a thrill, but this risk is a serious one because our pollinators are already at risk from pesticides, disease, and other parasites.
Core, A., Runckel, C., Ivers, J., Quock, C., Siapno, T., DeNault, S., Brown, B., DeRisi, J., Smith, C.D., and Hafernik, J. (2012). A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis. PLoS ONE 7, e29639.