Many of you have heard of the very scary phenomenon called "Colony Collapse Disorder" - and if you haven't, you should, because it could be a major threat to the food we eat. CCD is when the worker honey bees abandon their hives and die, which, if widespread, can mean drastic decreases in pollination of crops. This phenomenon was first reported in the U.S. in 2006 and ever since that time, scientists have struggled to uncover what was responsible. Everything from cell phone radiation to genetically modified crops to a variety of parasites of honey bees were suggested to be the cause. Then, today, a new paper in PLoS One showed data suggesting that another kind of parasite is linked to CCD. Apocephalus borealis is a parasitoid fly that was known to attack bumblebees and paper wasps, but now has been demonstrated to also attack honeybees in the U.S. - in fact, 77% of the colonies sampled near San Francisco were parasitized by A. borealis. The authors used DNA barcoding to confirm that the flies in the honey bees were genetically indistinguishable from those parasitizing bumble bees.The authors of the new study also found that bees that were found flying around at night (something honey bees don't normally do) were significantly more likely to be parasitized by the fly and furthermore, the sick bees also seemed disoriented. It is not currently known whether or not the tendency for the parasitized bees to fly at night away from their colonies is another example of manipulation of the host by a parasite or whether this might be an act of altruism by the bee, carrying its parasite away from its colony and thus protecting the others.
Although these new results are very exciting, many questions remain to be answered about the history and impact of A. borealis. First, when did the switch into honey bees occur? Honey bees are not native to the U.S., but since they are so well monitored and studied, the authors believe that the switch must have happened recently - otherwise it would have been noticed by apiculturists. Second, could these flies also be serving as vectors for other bee pathogens? Two known bee pathogens, Deformed Wing Virus and Nosema ceranae, a microsporidian were found in the A. borealis flies. And finally, could the invasion of honey bees by this parasite mean that CCD is going to increase? The natural hosts of A. borealis are bumble bees, which live in small colonies where only the queen herself survives the winter, but honey bee colonies have thousands of bees and their activity maintains some amount of heat, even in colder winter months. This increase in host resources and more generations per year could spell a population explosion of A. borealis...and that won't be good for those of us who depend on pollination - like all of us.
The image is from the paper. Look closely at the abdomen of the bee - that's a little parasitic fly laying eggs into it. Soon the larvae will emerge from the dead host. (You can see a photo of this in the original paper as well.)
Source: Core A, Runckel C, Ivers J, Quock C, Siapno T, et al. (2012) A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis. PLoS ONE 7(1): e29639. doi:10.1371/journal.pone.0029639.
Wow! I wonder what was the host of A. Borealis before it started using bees? And where did this fly come from? Can the migration of this fly be halted. I have so many questions. Congratulations to the "absent-minded" professor for this important discovery. No bees=No foods.
ReplyDeleteRelatives of this species are parasitoids of ants. Very good questions that you raise - I would bet that a lot more attention will be paid to these pesky flies now!
ReplyDeleteGive the bees a break. Now another pest to deal with. If they can live in South Dakota which is a cold climate they can probably live anywhere in the United States. Tough times for bees and beekeepers.
ReplyDeleteSo now that we know what's killing the honey bees, it's time to figure out a way to protect the bees, find out where these pests came from, why they're targeting honey bees all of a sudden, and kill these little pests if we can. If these parasites are the reason for the colony collapse disorder, then why are there so many bees dying all over the world? These parasites are not only inhabiting the USA, but they are everywhere!
ReplyDeleteThis is not the only threat to honeybees and most likely not the sole cause of CCD. My husband is a commercial beekeeper; the guy who helps pollinate the almonds you love. Well we have been fighting this battle of bee population decline for some years now. Every year a new part of the puzzle emerges but to date the whole picture has not been revealed. We try to deal with the problems we know but sometimes wonder if we may be making a problem in another area. And then there is the one factor we can't control, the weather. That has a big impact on the health and activity of our bees. We love our "girls" and hope that we can figure out how to protect their "families".
ReplyDeleteCwqnbee, you are absolutely right - it is very likely that multiple environmental factors and pathogens contribute to CCD. A few months ago, the podcast This Week in Virology discuss a paper (also published in PLoS One) which raised a possible link between CCD and infection by iridovirus and microsporidian parasites. You can find that particular episode of the podcast here:
ReplyDeletehttp://www.virology.ws/2010/10/24/twiv-104-the-colony-collapse-blues/
As a beekeeper and founder of the 2 Let It Bee, Inc. The Honey Bee Revitalization Project, I find this discovery very interesting. I will keep a more watchful eye out on our hives. I am more concerned if we have weakened the honey bee with the use of pesticides and having them pollinate GMO crops.
ReplyDeleteSeveral years ago my driveway was littered with dead and dying bees. The bees seemed to have recovered and are now very abundant,in my garden. Some dying bees are starting to show up again. I am collecting some of them, to monitor, to see if they are parasitized by the Phorid.
ReplyDeleteBeekeepers need to gather as many of the dead bees that are around their hives and keep them in jars so they can be watched for emerging parasites. Bees usually leave the hive as they are dying and these parasites eating them from the inside cause death; these bees can be found about the hive as they die; also dead dragged out by the housekeepers of the hive will be available to collect. Many of these dead bees around the hive may have died from natural causes and/or from something other than a parasite, but odds are if the parasite is affecting your hives you can be sure to discover that by collecting the dead bees and watching for a hatch.
ReplyDeleteWe have all this info on what they do, how do you control them , i have had a a lot of bees dead on the exterior of my hive and saw a fly come out of my hive yesterday, i swatted it down but couldn't find it. so i collected the bees and have them in a bottle for observation
ReplyDeleteWell, at the moment, we are at the stage where we know that they are killing bees and some broad aspect of their ecology, but not enough to control them. Indeed, as Cwqnbee pointed out previously, for all we know, these flies might not even be the main cause of colony collapse and that there might be other pathogens, environmental factors which are involved.
ReplyDeleteGreg, if any adult flies hatch out those dead bees you collected, you should definitely send them to an entomologist, or to a museum (if there is one nearby) so they can be properly identified and recorded.
"bees that were found flying around at night (something honey bees don't normally do) were significantly more likely to be parasitized"
ReplyDeleteWhen I read stuff like this I always wonder about things like: are the parasites more active at night so could it be that bees that fly around at night are more likely to encounter the parasite? Could it also be that something like urban lighting has had some effect on the behaviour of bees? Just my tuppence-worth.
Well, given that bees aren't normally known for flying around at night, this makes it more unlikely that their had behaviour predispose them to being parasitised, though it is also likely that the advent of artificial lighting has altered the "normal" behaviour of honeybees.
ReplyDeleteHowever, you have brought up a good point, which is untangling the casual chain of events - is the host behaving strangely because it is parasitised, or is it parasitised because it behaves differently? That is why scientists who study such phenomenon have certain criteria for judging whether the altered host behaviour is indeed induced by the parasite, and if so is it an intended outcome of the infection, or simply a side-effect (pathology).
However, as with everything in biology, just about everything lives in a grey area, and purposeful manipulation of host behaviour could easily have originally evolved from side-effects which are then selected for through natural selection and eventually become a specific adaptation.
With all my scientific reading I've now come to the conclusion that it's always worth asking that 'chicken or egg?' question. Correlation does not mean causation and all that.
ReplyDeleteBee parasites are one of my favorite parasites!
ReplyDeleteWhen I grow up I want to be a parasitologist.
How crazy is that. With out bees we could starve. Its really amazing when you think of it. How many other species that we rely on like this? How many do we not know about? My sister could die if she gets stung. Weird thing bees are. They live in huge colonies that protect the queen, and if something happens to her another steps up.
ReplyDelete