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Repeat after me: Nosema does not cause dysentery

Over the past year, Randy Oliver has published several informative articles in the American Bee Journal about the relationship between nosema disease and honey bee dysentery. If you haven’t read these pieces, you should. His message is simple: there is no evidence to support the theory that nosema disease causes dysentery.

I’m dismayed, however, that many beekeepers are still having trouble with this idea. People continue to insist their bees died of nosema based solely on the presence of feces on the frames or the fronts of their hives.

Correlation vs causation

I decided to take a different tack on this subject and start with the difference between causation and correlation. If you’ve never been able to understand the difference, don’t be alarmed. It’s never too late to learn.

To demonstrate the difference, many statistics books use the study done in New York City many years ago that showed that ice cream sales correlate with homicide rates. Every summer in the city, as ice cream sales increase, the homicide rate goes up. That is an interesting correlation, but does the sale of ice cream cause homicides? Or does more homicide whet our appetite for ice cream? Of course not.

Both of these events—ice cream sales and homicides—are affected by hot weather. People eat more ice cream in hot weather than in cold weather. Also, people tend to be more irritable and perhaps short-tempered in extreme heat. Some of those irritable, short-tempered folks are prone to staying out later in the evening, trying to stay cool, a situation that can spike the homicide rate.

Both the sales of ice cream and the increase in homicides were linked to a common cause, hot weather, but homicides did not cause an increase in ice cream sales or vice versa. In other words, the incidence of both events correlated: when one increased, the other increased. But that does not mean that one caused the other.

Nosema disease and dysentery

Likewise, nosema disease and honey bee dysentery often correlate. When one goes up, the other may go up, especially in a winter hive when bees are confined, but that does not mean that one causes the other.

Nosema: Nosema disease in honey bees is caused by a microsporidian, a tiny unicellular fungus that reproduces by spores. The fungus enters the digestive system of a bee through the mouth and travels to the midgut. There, a little spring-loaded lancet injects the bee’s epithelial cells with spores. Once injected into a cell, each spore reproduces by forming lots of copies of itself.

The spores interfere with the digestive enzymes that are normally produced in the epithelial cells. When the epithelial cells try to release digestive enzymes, they end up releasing nosema spores instead. With a lack of digestive enzymes, the bee weakens from malnutrition and may eventually starve to death.

Honey bee dysentery: Honey bee dysentery is a separate ailment. As you know, honey bee dysentery is not caused by a pathogen but by an excess accumulation of water in the honey bee gut. You can think of it as bee diarrhea. In cold weather when honey bees can’t get outside to defecate, they must hold their feces, sometimes for months. They are designed to do this, but if they consume too much liquid over time, they sometimes reach a point at which they can no longer “hold it” and they end up defecating inside the hive or on the front porch.  This unfortunate mess is what we call honey bee dysentery.

Two conditions can occur together

Your bees can have nosema disease with or without dysentery and they can have dysentery with or without nosema. One does not cause the other and one is not dependent on the other. If you see dysentery on the frames inside your hive or running down the front of it, the only thing you can conclude is that your colony has dysentery. To quote Randy Oliver in his May 2019 article, “The only way for a beekeeper to diagnose nosema infection is by microscopy.” If you don’t have it tested, you don’t have a clue.

On the other hand, bee colonies can easily have both ailments at the same time. Dysentery can be quite harmful to colonies because of the sanitation problem it creates. Many diseases are easily transmitted by fecal material, so if bees are defecating in the hive, there is a much greater probability that pathogens will be transferred from bee to bee, including nosema. So if a bee has nosema, dysentery can increase the rate of bee-to-bee transmission. However, if a colony is free of nosema, no amount of dysentery will produce it.

Timing causes confusion

Nosema apis shows up primarily in late winter or early spring, just like dysentery, so it is easy to see why beekeepers began connecting the two. It was only when Nosema ceranae—often a summertime ailment—began showing up with no signs of dysentery, that beekeepers began resurrecting the question about the nosema-dysentery connection. In the years of research Randy did, he was never able to find a single study that proved that either nosema species was a cause of dysentery.

I agree that we have to stop parroting what others are saying, wildly spreading disinformation like spores. When someone tells you their bees died of nosema, don’t be afraid to question them: “Did you have them tested?” If they say, “No, I didn’t have to” take everything else they say with a grain of salt. If they didn’t have those colonies tested, their conclusion is nothing more than a wild guess.

I highly recommend reading Randy’s May 2019 article, “It’s ‘Common Knowledge’ that Nosema Causes Dysentery…But is it Actually True?” He presents lots of supporting evidence from the work of others.

Rusty
Honey Bee Suite

In this example of honey bee dysentery, you can see bee feces that was deposited on the top bars. This colony could also have nosema, or not, so testing is required.
In this example of honey bee dysentery, you can see bee feces that was deposited on the top bars. This colony could also have nosema, or not, so testing is required. Photo by Debbie Fyda.
Bee feces has dripped down between the frames and landed on the combs. Any disease organisms living in the feces can be easily spread from bee to bee, including nosema. On the other hand, many nosema-decimated hives have no dysentery whatsoever.
Bee feces has dripped down between the frames and landed on the combs. Any disease organisms living in the feces can be easily spread from bee to bee, including nosema. On the other hand, many nosema-decimated hives have no dysentery whatsoever. Photo by Debbie Fyda.
Feces that lingers in the bee intestine for long periods tends to get darker and darker. In summer, when bees pass feces frequently, it often appears bright yellow.
Feces that lingers in the bee intestine for long periods tends to get darker and darker. In summer, when bees pass feces frequently, it often appears bright yellow. Photo by Debbie Fyda.

Comments

Gary K
Reply

As always, thank you. So in a TBH with bottom screen and bottom sticky board, IF the hive is struggling with dysentery would it be a fair assumption that it would probably show up to some degree on the sticky board? I realize logic says, well no duh, but the number one thing we have learned in our very short time with bees is logic don’t quite always fit the situation. Or at least not quite yet for us. Bee logic ain’t the same as ours.

Rusty
Reply

Gary,

I don’t know if it’s related to logic or not, rather it seems to be related to gravity. Wherever the bees are, the feces would end up below, right? So if the bees are on combs, the feces might be found on the lower part of the combs, or the screen, or the sticky board. There’s a saying for that, if you’ll excuse the expression, “S__t flows downhill.”

Sharon klemm
Reply

Helpful, as always. If a hive is experiencing a lot of dysentery should drawn comb be swapped out for new foundation? Or leave it alone?

Rusty
Reply

Sharon,

The bees will clean up the mess by themselves. However, if it contains spores of Nosema, you might want to replace it. If not, just leave it. It’s another good reason for testing.

Cheryl
Reply

Thank you for, in my case, this very timely article. Just this week I lost one of my hives. I wasn’t too surprised as mite counts this summer were ridiculous despite many treatments of varying kinds. While taking the hive apart I found dark brown feces on the tops of many frames and dripping down comb in several spots. I have never seen this before (this is my 4th year of beekeeping). No feces on outside of hive or on the landing board. I keep the front opening of the hive clear of dead bees so they weren’t trapped inside. Living in northern Michigan, it’s cold but there have been days decent enough for cleansing flights.
So now what? I’m assuming the contaminated comb hits the trash. But what about the frames? Should I send some of the bees out for testing? At a bit of a loss about the next step.

Rusty
Reply

Cheryl,

Your bees will clean the frames and polish the cells before reuse, so you don’t need to do anything. However, if the bees have nosema, you may want to sanitize the equipment before re-use.

Gary K
Reply

You be talkin’ to a farm boy…so it always flows downhill! With a little help from pitchforks and tractors!

Sharon
Reply

This is the first time in my short 4 year history of working with bees that I have heard this! Nosema and dysentery have always been tacked together like “horse and carriage”. GREAT article. Always good to learn new things and to un-learn wrong things. Thanks. Sharon

Debbie in Ohio
Reply

Average of 4.35 million spores present per bee! Nosema (sp.)

Debbie in Ohio
Reply

ABJ Feb. 2020, Page 205 … What I find fascinating in all of this is: “…Alfonsus’ measurements: Dysentery appears when the fecal accumulations reach 33% of the total body weight of the bees. General defecation does not take place until the accumulation reaches about 45%. That 33% accumulation occurs when a bee is holding around 35 mg of water in its rectum. …” That’s quite a bit for such a tiny bee. I found this article to be so fascinating. The article goes on to talk about how bees deal with excess water over the winter. Everyone should read this article. Some great new information here. Especially the part about winter brood rearing.

Thanks Rusty for “Feces that lingers in the bee intestine for long periods tends to get darker and darker. In summer, when bees pass feces frequently, it often appears bright yellow.” Where did you find such a tidbit? An eye opener. It’s nice to know that if I see this again, it can possibly be just dysentery.

The only reason I thought this hive had Nosema was because I had three in total, all were queens that I purchased from elsewhere. It was kind of weird to me that these three hives had it and all the others did not. Coincidence? Or will queens purchased come with it and give it to a hive? Please advise.

I did send the bees in for testing and it was 4.35 million spores present ‘per bee’ !! YIKES ! If it’s not one thing with the bees, it’s another.

Thanks Rusty.

Rusty
Reply

Debbie,

That color observation is in my notebook from the master beekeeper course I was in. However, I didn’t remember who said it, only that it came up in discussion.

Debbie in Ohio
Reply

Thanks Rusty. I am always looking for new things to learn and read about. So much is redundant or does not make sense.

Michael Duncan
Reply

The issue of dysentary wasn’t addressed in this thread! If you’ve got “it” what to do to treat it.

Rusty
Reply

Michael,

Since it’s not a disease, you don’t treat it. As soon as the bees have a warm day, they will take cleansing flights and the dysentery will disappear.

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