A Basic Lesson in Nosema

Contributed by Susan Shank and J. Morgan 

The June 2015 SIBA Moores Hill meeting was somewhat of a milestone for our group. As of now, we're capable of testing for nosema, and we not only viewed some real nosema spores under a microscope at the meeting, but we also captured some images and video of the spores in action.

This spring was bitter-sweet for me personally. Sweet that my mite testing has been highly effective and proven by recent lab results... and bitter in that my samples did come back with nosema... also proven by recent lab results. I send at least 3 samples per year to the lab... primarily to confirm if my own testing is accurate and effective. Never have the samples come back with nosema. However, if you think about it, you would typically collect young brood bees for a mite test, but older forager bees for nosema tests. When I sent off the most recent sample, it was only young nurse bees. For the sample to come back with 4.45 million spores per bee was quite discouraging... and surprising that they found that concentration in young bees.

In the midst of everything else I have been watching with the bees, nosema is something that I have not been diligently testing for, nor mitigating. It completely explains the massive decline I experienced with 4 hives just before the locust bloom this year. 

Read it and weep. My first results that have come back positive for nosema...
but notice, 0 mites. Looks like it's time to shift focus to the next challenge.

It's clear that I have to rethink my cultural practices entirely. I have reused equipment and frames without a lot of thought. I have culled out the nastiest looking frames but I realize it's time to up the scrutiny on frames and equipment. Currently, I have new queens laying in the same hives that have these spores, so now it's a race to see what can be done before the winter. But, that's another blog.

Let's talk about what we learned last night at the SIBA meeting. Thanks to Susan Shank who has worked very hard to go out and research nosema and organize the facts as she presented to us at the meeting. Her presentation was understandable, and it opened our eyes to get us thinking about, and preparing for this real issue.

Most beekeepers have experienced that odd phenomena where a hive just doesn't seem to build up the way it should. It sputters and struggles all year long with no explanation.

What we now know... is we could be watching the bees starve in slow-motion. It's a gut disease that makes it so the bee cannot metabolize its food. As spores multiply, the problem worsens.

The following is Susan's presentation, edited for brevity. I have taken some liberties of my own and in no way mean to change or contradict her research. I consider the body of work solid, with my personal intention to serve it up in a way that is interesting and informative. Thanks again Susan.

What is Nosema?

Nosema is a unicellular fungus tha is the most widespread of all honey bee diseases. The dormant phase is the spore. These spores are very resistant to temperature extremes and even dehydration. That means you don't get rid of it by accident.

Nosema Lifecycle

Bees eat spores which germinate in the gut. This vegetative phase infects the epithelial cells lining the bees gut. Within 6-10 days, a gut cell may have up to 50 million spores. In normal bee biology, the epithelial cells are shed to release digestive enzymes. When infected cells are shed, they release millions of infective spores into the gut.


Bee digestion of pollen/nectar is impaired. Bees can starve in midst of “plenty” of honey, pollen and resources. Foragers (and MAB's, mature adult bees) are most infected because they have been exposed to the spores longer. Foragers and MAB's have decreased lifespan and the loss of workers outside of the hive *may* be one aspect of colony collapse disorder (CCD). There is typically minimal infection in queens and drones because the infected bees do not attend to them. Queens are not well-fed, and supercedure of queens increases. MAB's are often forced to forage earlier in their life.

Which Nosema? Apis vs. Ceranae

N. Apis has been spread world-wide in honey bees for many decades. It has classically been identified by bees that can’t fly, feces on combs, piles of dead and dying bees and slow build-up in the spring. Spores see an increase during spring expansion but not as much in hot weather. The spores are spread mainly by feces in the hive.

N. ceranae has only been commonly identified in hives since circa 2005. It is biologically more virulent (meaning it is more severe, and spreads more efficiently). It infects shed epithelial cells and basal cells and spreads cell-to-cell. It's not affected by the heat of the summer. Spores are stored in pollen and are stable for many years. There is no clear sign of infection in the hive other than “failure to thrive”.

Let's not think of nosema as a bee disease, but a hive disease. Again, it is first seen in foragers.   Over-wintered brood can yield some recovery, but increased spore exposure via pollen leads to more house bees infected. Queens start to die from lack of feeding.

So how do we determine if Nosema Is present, or is at a dangerous level?

The simplest way to identify Nosema is by looking for spores using a microscope. Spores from apis and ceranae are essentially identical morphologically. To really know that you have, apis vs. ceranae requires molecular testing (PCR).

Traditionally, nosema apis was tested in bees at the front of the hive entrance (foragers). Treatment decisions were made by a bulk estimate of spores per bee > 1 Million spores per bee warranted treatment.

Now that N. ceranae has become the more serious threat, detection methods are under dispute.

  • Which bees to test?
  • Bulk estimate of spores per bee?
  • Examination of prevalence (% of bees infected)?
  • What difference does it make anyway?

Which bees to test?

Forages are first ones to be infected, so they may be the best bees to test for a +/- decision. Infected house bees may be a more clear indication of a threat to the hive and more people appear now to be sampling inner cover/top of frames bees (MAB's, middle-aged).

Testing Methods

Bulk estimate of spores per bee
This is the most widely used method and available from national labs. It uses frozen or alcohol treated bees and can be done with total bee or abdominal preps. It gives fairly exact counts. However, it's not clear with N. ceranae what the treatment threshold should be and it's also not clear what sample size should be (probably varies with the time of year) Newer studies indicate that one or two highly infected bees strongly alter the results.

Examination of prevalence (% of bees infected)
May correlate better with hive strength. Still not clear where to sample since “areas” of the hive may be more or less infected. Sample size of 5-10 bees appears adequate and since infection can occur over days, sequential testing is a must.

Interpretation of Results: 

0.5 ml/bee determine few/mod/heavy (or exact counts using a hemacytometer)

0/5 or 0-1/10 = OK
3/5 or 4+/10 = more than 30% of bees infected which probably is influencing hive behavior

What to Do?!

Fumagillin B in syrup/spray/drip. Does not kill spores but decreases rate of spore production. It is very unstable in syrup. Ideally, it is stored in honey where it's more stable. You should treat it as a chronic infection. Infective spores will be in the hive for years. The first priority is overall nutrition! Protein supplementation may help more than drugs, but very sick bees cannot eat.

Downside of Fumigillin

  • Not recommended to use in foraging season due to increased risk of residue in harvested honey
  • Fumagillin is toxic to humans and bees
  • As concentration in hive honey stores decrease, N. ceranae spore proliferation may actually increase faster than no treatment because the low level of fumagillin still inhibits bee gut function
  • Requires minimum of 4 week treatment
  • Does NOT eradicate infective spores
  • Essentially all studies show that spore counts rebound within 6 months

Possible approach that we discussed in the June 2015 meeting

  • Do 5-bee assessment from top cover in early spring.
  • If heavily infected and build up is slow, then treat
  • If build up is OK – wait – always use pollen patties
  • After honey is off, test again
  • If newly or still heavily-infected, treat
  • Repeat testing in the fall
  • Treat only with greater than 30% infected in several examinations over a couple weeks.

The above is a basis... and is subject to change as we as a club better understand nosema and it's wrath.

But I don’t have a microscope!

SIBA Moores Hill will be conducting one or more Saturday Workshops. Susan Shank will demonstrate how to prepare samples and test them. At the workshop, anyone who wants to learn can understand how to show other how to test. We plan to set up 1 or 2 microscopes at home-base, and maybe elsewhere so that samples can be processed before or after meetings, or at other planned times.

Watch for a sign-up for the first workshop soon!

Here is video of a wet-prep slide

Unfortunately, this is only at 200x. The nosema spores are visible, but small. Most of the other stuff around it is a distraction. We'll work to get a better video soon, but it was cool to be able to capture this in the midst of our first trials.

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