Parasitic Fly Threatens Honey Bee Populations

Honey bee colonies around the United States are in decline, threatened by several different diseases and parasites. John Hafernik, a professor of biology at San Francisco State University, describes how a parasitic fly that was thought to prey upon bumblebees may pose a new threat to honey bee populations in the U.S.

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IRA FLATOW, HOST:

This is SCIENCE FRIDAY. I'm Ira Flatow. The honeybee, as we've all heard, is in trouble: various fungus attacks, infestations of tiny mites in the hives and to top it off the mysterious ailment known as colony collapse disorder, in which the bees mysterious disappear from their hives.

Now there is a new threat: A parasitic fly once thought to be only a problem to bumblebees has been found to be attacking honeybees as well and turning the honeybees into zombies. They leave the hive in a daze, they form into groups, just like the living dead do in the movies - except these bees eventually die.

Joining me now to talk about the find is John Hafernik, he's a professor of biology at San Francisco State University and co-author of a report on the find in the journal PLOS One. Welcome to SCIENCE FRIDAY.

JOHN HAFERNIK: Pleased to be here, Ira.

FLATOW: How did you discover this parasite?

HAFERNIK: Well, you know, a lot of people think that science is a carefully planned occupation where everything is thought out ahead of time. But this is really something that happened by accident. I'm not normally a honeybee researcher, but about three years ago now, I was walking into the biology building at San Francisco State, where I work every day, and I noticed that in front of the building, there were a number of honeybees that were laying on the sidewalk in front of the building.

Some of them were walking around in circles, some were in kind of a bee fetal position, and I thought that was strange, but I also saw it as an opportunity. But not as an opportunity to do research, but an opportunity to feed a praying mantid that I'd brought back that weekend from a class field trip with my entomology class.

So I scooped them up in a vial, brought it down to the mantid, fed the mantid the bees, and she loved them. And in fact, I did that daily then for several days. Eventually she produced a number of egg masses for us and was very happy eating the bees.

But as luck would have it, one day I went up to my office first, on the fifth floor, and put the vial back onto my desk someplace, amongst the variety of papers - you can imagine my desk. And then left it there, forgot about it. Didn't notice it for another week or so, came back and the vial was filled with dead bees and maggots that were crawling out of them and some small brown pupae that were the pupae formed by those maggots.

And that's when I knew there was something strange happening to these bees.

FLATOW: So the maggots, because they were in the vial, sealed up, the maggots had to be coming out of the bees.

HAFERNIK: That's right, no place else for them to come from.

FLATOW: And so you discovered that there was a tiny fly that was the parasite?

HAFERNIK: Right, so it took a little detective work, another two weeks or so before the flies hatched out of their pupae and I could tell what they were. And I recognized them as being phorid flies, it's a group of flies that some are parasites, some are kind of scavengers, and I knew the phorid expert was Brian Brown at the Natural History Museum of L.A. County.

So I called him up and then sent him examples, and he recognized them immediately as a native fly that normally feeds on bumblebees and paper wasps, but had never been found in honeybees before.

FLATOW: And how does it attack the honeybee?

HAFERNIK: Well, the way it attacks the honeybees, is that the female lands or chases a honeybee down and lands, gets on its back, her back, and then finds a weak spot. And honeybees have plates on their abdomen that are hard, but in between those segmental plates are membranes that allow them to be flexible.

And the female finds those flexible membranous areas and has an ovipositor, it's kind of a hypodermic needle-like structure that she inserts in and starts injecting eggs into the abdomen of the bee.

FLATOW: And so then that reacts with the bee and sort makes the bees act like zombies?

HAFERNIK: Well eventually. What happens is that those eggs hatch, and they hatch into little maggots, your fly larvae, and begin feeding on the internal contents of the bee, and at some point as this goes along, it starts modifying the behavior of the bee such that the bee does things that bees don't normally do like flying out of a hive at night.

And if there happens to be a light nearby, then like many insects that are flying around at night, it'll get attracted to that, and eventually these bees become kind of comatose and fall under the lights.

FLATOW: And so they - you find them on the floor underneath, on the ground underneath...

HAFERNIK: Yeah, and so I - it took me a while to figure out why they were in front of the biology building. I often walk with my head looking down, looking for interesting things in front of me instead of looking up. If I were an ornithologist, maybe I'd be looking up more.

(SOUNDBITE OF LAUGHTER)

HAFERNIK: So later I went out and looked up, and it was right under the lights at the biology building. They were coming up, and we have a bee hive right next to the north part of the biology building. So they were literally flying a beeline from that bee hive to the light.

FLATOW: But in your paper, you're sort of sounding an alarm. You're not just pointing out some interesting phenomenon under the street light in front of your lab, but that - you think there's a real danger this could be spreading or taking over the bee population?

HAFERNIK: Well, we think we need to be careful about this because this is a native fly that's now expanded its host range into a non-native species, the honeybee. So this is something the honeybee hasn't experienced before, and potentially it could be a bigger problem for that species, since it hasn't co-evolved with its parasite.

We don't know exactly what the extent of the problem is at this point, and some of the accounts I've seen in the media have been - have overstated what we're trying to say. We're not saying we found the solution to colony collapse disorder or that this is going to kill all the honeybees across the United States, but it is something we need to take seriously and to monitor closely to find out indeed how important this is going to be for survival of honeybees.

FLATOW: If you're a beekeeper with your own hives, can you look for symptoms of this, or is it obvious to you?

HAFERNIK: Well, it's probably initially not very obvious because the bees, as best we can tell, leave the hives at night, and so that's not a time when people mostly notice things. And also bees are always leaving hives, even during the daytime. So the unusual thing, of course, is they don't come back.

But one of the ways beekeepers can monitor this is to set up a light next to their beehives and turning it on at night and see if they are attracting bees coming from their hives at night, if they are then to capture those bees and isolate them, either in a small vial or even an envelope or something like that, and leave them for a week or 10 days and then look and see if there's - if there are fly maggots or fly pupae surrounding those bees.

FLATOW: I'll bet you it took you a while to go out and collect a lot of bees, usually.

HAFERNIK: Yeah, we've collected literally 10,000-plus bees as part of this study so far.

FLATOW: You must have had a lot of grad students out collecting.

HAFERNIK: No, this was very much a group project, and it's not just my work, it's the work of a number of students at San Francisco State University. Andrew Core is the lead author on this paper. He did a lot of the work. Jonathan Ivers has done a lot of work with beekeepers in the Bay Area and so on.

FLATOW: Now the paper's been out a while, a few days actually. What kind of reaction have you been getting? People are saying, you know, I've seen that, I just didn't know what it was. Or gee, I've never seen anything like this.

HAFERNIK: I've had emails from all over the world, from people describing behaviors that they've seen in bees, some that sound similar, some that probably are not closely related. And if someone out there has sent me an email, and I haven't answered it, I'm sorry, I haven't had time to answer all of those yet.

FLATOW: Do you want to hear from other people?

HAFERNIK: Well, we're interested in hearing about similar kinds of situations, especially if someone is willing to take enough time to isolate some of these bees and see if indeed they are getting larvae out of them because if they're getting the fly larvae out, then that's a pretty sure sign that they have parasitized bees.

FLATOW: Do we know that the bees may be passing them bee-to-bee within hive or between hives?

HAFERNIK: Well, at this point it looks like it's probably mostly happening outside of the hive with foraging worker bees, but we have observed pupae of the flies and pupal shells, which means that the pupa has actually hatched, in one of observation hives that we've been looking at. And I've even seen a worker bee carrying around one of these pupae, maybe trying to get rid of it from the hive.

So there's a potential for this to happen within the hive, as well as for them to get infected outside. It's much more serious if it happens inside the hive because the potential there is to infect not only the foraging bees but also the nurse bees and perhaps even eventually the queen. We haven't seen that yet, though.

FLATOW: Yeah, any speculation of why this might be happening now? Or might - it's not been going on for years, obviously, or people might have noticed it?

HAFERNIK: Well, we don't know exactly how long it's been going on. We know it's been going on for at least three years now, that's when we first discovered it. In this part of the world, honeybees have been around here since the Gold Rush days. So they've have 160, 170 years to be around these fly parasites. And we don't know how soon the flies actually were able to exploit a new host, the honeybee.

We suspected it might be relatively recent because the behavior seems aberrant, the fact that they show up at lights, and we don't see a lot of reports of that before, and now we're hearing more of that, but exactly when it happened, we don't know.

FLATOW: Yeah, tell me about the bee gene chip.

HAFERNIK: The bee gene chip, yeah, this is from Joe DeRisi's lab at the University of California San Francisco. So this is a microarray. It basically has little bits of DNA on it from various kinds of organisms, viruses, bacteria, nematode worms and varroa mites, things that might parasitize a honeybee.

So - and now our fly on that chip as well. That means that we can take a sample from bees that are collected out of hives virtually anywhere and then use the microarray to detect DNA from these different kinds of organisms, and if we get a positive hit, as we have in some cases with the fly, then we know that the DNA of the fly is there, and so the fly must be there, as well.

FLATOW: Is there anything to do if you discover that your hive is infected with these parasites?

HAFERNIK: Yeah, at this point we don't have a cure or a set of instructions of how to handle things. I mean, setting up a light trap next to the hive might attract the infected workers, and then if you kill them and dispose of them, that might help a little bit in transmission. But other than that at the moment, we don't have a cure.

We're hoping that as we learn more about the relationship between the fly and the bee and how it recognizes its host and what the important cues are that maybe we can find a weak link in that chain, and that can be used to break the cycle.

FLATOW: Well, we have a lot of beekeepers who listen to SCIENCE FRIDAY. So maybe you'll get some help there, and...

HAFERNIK: Well, maybe so, and beekeepers have been really wonderful in working with us on this project. They're a special breed of people.

FLATOW: Thank you very much, and good luck to you. Thanks for...

HAFERNIK: You're welcome.

FLATOW: Thanks for taking time to talk with us about this. John Hafernik is a professor of biology at San Francisco State University and co-author of this bee report, finding this incidence in the journal PLOS, Public Library of Science, One.

We're going to take a break, and when we come back, we're going to talk about the winter. Where do the bees go in the winter? There's a question, right? You don't see the bees around in the winter. They do something really interesting during the winter in the hive, but everything that happens in the winter, changes of seasons, we're going to talk about this science of nature in the winter. So stay with us. We want to hear what you think. We'll be right back after this break.

(SOUNDBITE OF MUSIC)

FLATOW: I'm Ira Flatow, this is SCIENCE FRIDAY from NPR.

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