A new parasitic phorid in honey bees

Female Apocephalus borealis specimen

Lots of press coverage is swirling around our recent paper in PloS ONE: “A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis”, available here . Note, I use the term “our” advisedly, as I am 7th of 10 authors, and thus cannot take much of the credit for this work! Unfortunately, some of the press coverage this publication is garnering is incorrect, but I’ll let my colleagues at UCSF handle that on their website. What I’d like to concentrate on is the phoridological context of this story, particularly on the genus Apocephalus.

Genus Apocephalus consists of about 300 described species, virtually all of which are found in the New World. I am pretty sure that species described from other regions do not belong in a group with the rest of Apocephalus. In the 1990s, I revised about half of the genus, describing over 200 new species, but there are still many more out there. Right now I have a grant from the National Science Foundation to revise the rest of them.

Current classification of this group places the species in 2 subgenera: Apocephalus and Mesophora. Species of subgenus Apocephalus are the original “ant decapitating flies” like the ones I videoed in Brazil a few posts ago. Subgenus Mesophora have very different hosts, however. Most of the known species are parasitoids of fireflies and soldier beetles, an extremely different group of hosts from the ants the others attack. In addition, I have described a few species that attack stingless bees in the tropics.

One species always stood out, however, and that was Apocephalus borealis. This crazy thing had been reared from bumble bees, yellowjacket wasps, and a black widow spider! It seems as though A. borealis has an extremely wide range of host acceptability. Perhaps this is what allows it to switch into new hosts, such as honey bees. We know that honey bees were not the original hosts, because they are an introduced species in North America. Probably bumble bees are their main hosts, but who knows? This species is only recorded from North America.

My colleague, Dr. Paul Smith, and I are currently studying the relationships among species of Apocephalus using molecular characters (DNA sequences), as well as morphology (body structure). Once we have a good phylogeny of Mesophora, we should know more about how the flies have shifted hosts through the group.

Apocephalus borealis on bumble bee, photo by K. O'Harrow

Of course, besides many new species to be discovered, many described species do not have any studies about their way of life. Particularly intriguing are some species from Costa Rica that seem to be closely related to A. borealis. Perhaps they are parasitoids of tropical bumble bees, but nobody has studied this yet.

One other thing to note: Apocephalus borealis is far from the only phorid that parasitizes honeybees. In South and Central America, many species of Melaloncha bee killing flies will attack honeybees, and we have even seen the tiny, 1 mm long Styletta crocea trying to attack these relatively giant hosts. Finally, Pseudohypocera kerteszi is an occasional past in honey bee nests, although they are much more prevalent in the nests of stingless bees. I will write more about these other bee parasitoids in future blog posts, but you can see photos of the flies on my website phorid.net.

In summary, it’s great that some phorids are getting press, and I’m sure we are going to learn a lot about this species because of its agricultural importance. Kudos to the (other) authors for their fascinating work. Don’t forget, however, that Apocephalus borealis is only one of about 4000 described species, and many more have amazing life histories still to be discovered.

9 comments to A new parasitic phorid in honey bees

  1. Dave says:

    Thanks for the additional information on these interesting flies. The more I learn about the Diptera, the more interesting they become. I suppose I should stop assuming every phorid I find is a Megascelia and start keying more out (but the MND generic key does give me headaches).

    When I read the abstract I was skeptical that the colonization of honeybees was necessarily recent, but you and your coauthors make a good case in your Discussion that at least the prevalence of infection has increased recently. A fairly typical pattern for animals colonizing a new habitat is a latent period when they are limited to a small area and then a sudden expansion. I’d think that this is a great opportunity to look for recent genetic divergence in the honeybee population(s) compared to the others (although I don’t suppose infected bumblebees end up flying around lights? Probably not, that would be too easy).

    PS – please excuse the pedantism, but you may want to change subfamilies to subgenera in the first sentence of the third paragraph?

  2. aep says:

    very interesting information. I read today a little about pseudacteon curvatis, if not mistaken, that’s the ant-decapitating phorid fly. according to what i read, both it and a. borealis are part of the metopininae sub-family. is this correct, or are these also apocephalus as you’ve mentioned above? that would make pseudacteon a sub-species of apocephalus just like a. borealis. its ironic how one is helping to lower the number of red imported fire ants while the other is producing the opposite effect by lowering the number of bees.

    • phoridae says:

      Both Apocephalus and Pseudacteon are genera in subfamily Metopininae. Note Apocephalus borealis is a species of Apocephalus, not a subspecies. Thanks for your comment.

  3. Kimberly G. O'Harrow says:

    So do you suppose the reason the phorid flies move from one host to another is simply because they lower the population in a given host while their (phorid fly) population stays high? If there are so many unidentified species feeding off new host insects it would seem a possibility. Thank you Brian for using my photograph. Kimberly G. O’Harrow

  4. Chuck Rupe says:

    I live in Colorado Springs, Colorado and have had an usually large and long fly infestation this year and have resentley notice the honey bees that have a nest in a neighbors garage wall swarm to my security lights when they are on at night, which I thought it was odd to see them out at night. Could this be due to our high population of flies this year and is this why they don’t seem to be going away?

    • phoridae says:

      Maybe. If you can send me some flies, or photos of them, I could verify that you have Apocephalus borealis. This would be of interest to me. Thanks, Brian

  5. Alice Liboiron says:

    Hi Brian,
    I’m researching an undergrad project on this spillover from Bumblebees to honeybees on the West Coast, and I’m wondering if you can tell me anything about A. borealis’s native distribution. Are they known to be historically concentrated on the West coast, or have they always been seen to be all over the continent?

    • Brian Brown says:

      Hi. There isn’t much historical data on Apo borealis, but what records are known are summarized in my 1993 paper on subgenus Mesophora. You can download it here.

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