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The “Nosema Twins” – Part 4 Treatment

The “Nosema Twins”

Part 4 Treatment

© Randy Oliver


First Published in ABJ in March 2008

Beekeepers had a hard enough time dealing with Nosema apis. What can we do about N. ceranae? Unfortunately, we are currently not very far up the learning curve. The best we can do is to take what we know about N. apis prevention and treatment, and modify it to hold our own against ceranae.

N. ceranae can clearly be devastating to colonies, yet we’ve still to learn what causes it to flare up, and its interaction with weather, nutrition, mites, and viruses. Its role in CCD is not yet clearly defined. I applaud the various hardworking CCD researchers in their assorted and sundry approaches toward solving the problem (or problems)—in the process we’re learning a great deal about the health and disease issues of our bees.

Notes from the 2008 ABF/AHPA & American Bee Research Conference

The Spanish team of Drs. Mariano Higes (pronounced Ee’ hase, with a strong “h”), Raquel Martín-Hernández, and Aránzazu Meana gave compelling presentations detailing their investigation into Spanish colony collapses. They found N. ceranae to be the culprit. The symptoms appear to be strikingly similar to CCD (however, it is clear that there are colonies collapsing in the US without detectable nosema). Drs. Steve Pernal and Tom Webster independently presented findings on treatments, and Dr. Judy Chen showed incredible graphics on the genetics and molecular biology of the beast, plus details of the progression of infection within the bee body. I will discuss information from these, and other presenters elsewhere in this article, and cite them as “2008 Conf.”

Genetically, N. ceranae appears to be cousin to N. apis, rather than sibling. Evidence presented separately by Geoff Williams and Judy Chen indicate that ceranae is more closely related to N. bombi (from bumblebees) or N. vespula (from wasps and some other insects), which helps explain why the European honey bee lacks resistance to it, and suggesting that it may spread to other bees.

Don’t expect to diagnose nosema infections without a microscope–Chen and the Higes team both found that ceranae infection does not produce dysentery, swollen abdomens, a white gut, nor “crawlers” (although I find a few infected crawlers in my yards).

Higes and Meana explained that the pathogenesis of ceranae infection in a colony progresses through four stages:

1. Asymptomatic-–the infection builds slowly the first year, goes unnoticed, but can be detected microscopically in foragers.

2. Replacement–The bees rally by rearing more brood, even through winter.

3. False Recovery— This may occur the second summer, during which the colony rebounds somewhat. However, in this phase the infection starts to move into the house bees.

4. Depopulation and Collapse–Finally, the bees “lose ventricular function” (they can no longer digest food), stop eating (and stop taking medicated syrup, or pollen supplement), and simply starve to death in the midst of plenty. Most adults die far from the hive, leaving only a handful of young bees and the queen.

Colonies can collapse either during summer or winter, but the character of the infection differs. During cold season collapse, most bees are infected, and spore counts exceed 10 million spores per bee. Contrarily, under warm season breakdown, less than half the bees are infected, and spore counts are generally much lower. Forager bees just die in the field, and the colony shows no symptoms other than dwindling away.

The Spanish researchers generally don’t count spores, however. To them, a colony is either “clean,” with zero spores, or infected, and on its way to eventual collapse unless treated with fumagillin. This knowledge makes accurate spore counting rather moot, and home diagnosis with a ‘scope even easier. When you first start finding spores at a low level, it means that you’d better start taking action, and don’t expect the colony to deal with the disease by itself. In subsequent correspondence, Dr. Higes asked me to make clear that the percentage of bees infected is of more importance than overall spore count.

I asked Dr. Meana if she thought that the Spanish bees were more susceptible than other European races—she was sure that they weren’t. However, it’s possible that the strain of ceranae that we have in the U.S. is not as virulent as the Spanish strain. Note that not all European researchers feel that infection by ceranae is invariably fatal.

What I’m seeing in California

Please remember that I’m new to nosema, haven’t treated for it in twenty years, and never looked for spores until a few months ago (but I’ve looked at hundreds of samples since). The question to me (and others) is that since ceranae has been in North America for at least a decade, why hadn’t we seen massive losses before last year?

After checking dozens of samples from various yards in my own operation, and those of friends (especially of lagging colonies, dinks, and deadouts), I’ve found some trends. First, there appears to be a large location factor, possibly due to nutrition. Some yards have zero spores, whereas in others nearly every colony is loaded. Most of our dinks and deadouts (even those with dead bees in front) showed zero to low spore counts (although a few showed moderate counts). This is opposed to the high correlation of nosema presence in CCD colonies (Cox-Foster, et al 2007; Bromenshenk, pers comm). However, my late splits that just wouldn’t build up were loaded with spores, and dwindled badly in fall.

After hearing Higes’ presentation, it is tempting to blame CCD solely on N. ceranae. However, it is clear that there are other factors or pathogens engaged in some colony collapses. Whether ceranae will become a major factor in colony losses in our future is yet to be determined, yet likely. In any case, it would be prudent for beekeepers to monitor nosema levels in their operations, and to understand their management and treatment options for dealing with this parasite.

I will spend the rest of this series first investigating treatment options (beginning with Fumagilin-B®), then alternative drugs, management techniques to minimize infection, and, finally, comb disinfection options.


Hundreds of compounds have been tested to control nosema in honeybees (Moffet, et al 1969; Pernal 2008 Conf)–few have found to be effective. The only registered treatment for nosema in North America is fumagillin, a natural extract from the fungus Aspergillus fumigatus. Fumagillin has a long history of successful use against N. apis. Higes (2006) demonstrated that it is also effective against N. ceranae. It does not kill the spores of either species, but can greatly reduce spore production, and the overall infection rate within the colony. Fumagillin has traditionally been recommended for application in fall and/or spring for N. apis, but this recommendation may need to be revised for ceranae.

Fumagilin-B is the only approved nosema treatment in North America. It has been demonstrated to be effective against Nosema ceranae.

The sole supplier of fumagillin in North America is the Canadian company Medivet, and their product is named Fumagilin-B (see CHC 2005 for more info). The general strategy for using fumagillin is to feed it in heavy syrup so that the bees store it as “honey” above the brood nest, so that they will later eat their way up into it, and thus dose themselves for an extended period of time. According to Medivet owner Willy Baumgartner, once fumagillin is mixed into syrup, there is a fairly rapid loss of potency, so it should not be stored for long periods. However, after the bees process it into “honey,” it retains considerable potency (Furgala & Gochnauer 1969). Kochansky and Nasr (2003) found that fumagillin can tolerate some exposure to sunlight, although others suggest using opaque feeder jars (Meana 2008 Conf).

The long residual life of fumagillin in honey has led to its being banned in several other countries, for fear of honey contamination. Be careful in its use not to treat when it is likely to be stored by the bees in honey for human consumption. Cummins (2007) cites its uses in human medicine, and possible genotoxic effects.

Be sure to follow label directions and to give the full dose. Multiple studies have demonstrated that treating colonies with less than the recommended dosage may be ineffective. There are different treatment protocols in various countries, but the general strategy is to give the colony a continuous dose for at least 4 weeks, either by having them store a month’s worth of heavy syrup to feed upon, or by treating weekly with a smaller amount of light syrup, intended for quick consumption. Fall treatment with fumagillin is effective when fed in excess heavy syrup which is stored for winter feed . Spring treatment is also recommended in syrup, but some researchers have found spring treatment with fumagillin in pollen patties, dusting with powdered sugar (multiple dustings), or in a sugar/oil patty to be effective (Wyborn 1987, Szabo 1987a,b). Please note that note that non syrup application is not an approved method! Some researchers have also suggested stronger doses to be used in Canada (Szabo 1987b).

I’ll summarize the label directions below, since some purchasers (such as myself) may not be given the required package insert with a purchase.


Preparation of Medicated Syrup (adapted from Medivet package insert)

Use 4.5g Fumagilin-B per gallon of heavy syrup (for small quantities, a rounded tsp per gallon is close enough).

Fumagilin-B will dissolve in room temperature water or syrup, but is most easily dissolved in warm (95 -122°F) water before adding the sugar.  Stir well to evenly distribute the medication in the syrup.  Do not feed immediately prior to a honey flow.

Fall Feeding Medicated Syrup

2 gallons for each 2-chamber colony (approx. 30,000 bees)

1 gallon for each 1–chamber colony (approx. 18,000 bees)

¾ gallon for each 5-frame colony (approx. 8,000 bees)

Feed additional unmedicated syrup to desired colony weight for wintering.

Spring Feeding Medicated Syrup

1 gallon for each 2-chamber colony (approx. 20,000 bees)

½ gallon for each 1-chamber colony (approx. 12,000 bees)

½ gallon for each 5-frame colony (approx. 8,000 bees)

1 gallon for each package colony

There are some differences in opinion regarding the details for feeding Fumagilin-B. The label states that if the colony requires feeding of unmedicated syrup for stores, that such feeding should be done after feeding of medicated syrup. However, some authorities recommend instead that feeding for stores be done before the medication, so that the medicated syrup is the last thing stored in the broodnest, and is thereby not diluted or covered by unmedicated syrup.

I went straight to the horse’s mouth, and asked Willy Baumgartner to clarify. His point is that each colony may have different winter feeding needs. Therefore, he suggests that the medicated syrup be fed first, in order to make sure that each colony gets the appropriate dose, and then do any further feeding to top off stores as you’re able. He feels that this strategy offers good protection against both nosemas.

Others, however, question whether the colony will actually consume the proper dose of fumagillin during the initial feeding, or whether they will simply store it. So we have conflicting recommendations for fall feeding. “Medicate last” makes sense to me if you are sure that the weather will allow you to finally get the treatment in. The “medicate first” strategy may be more appropriate in northern areas where winter can set in without warning.

Willy also had additional suggestions regarding spring feeding:

“With the arrival of Nosema ceranae we need to change the spring treatment method to more or less provide the same spring dosage as for Nosema apis, however, we like this to be divided into 4 separate treatments (1/4 dosage each) one week apart. This is similar to the successful Spanish experiments, except that we are using a little bit more sugar syrup because the bees may need it anyways. This spring treatment will be tested and worked on beginning this spring by Dr. Stephen Pernal, Canada Agriculture Research Station in Beaverlodge, Alberta.”

Update 1/20/2011: For the small-scale beekeeper, feeding 1/3 tsp of Fumagilin-B in a cup of syrup, weekly for 4 weeks, would likely be the most effective treatment.

Note in the label, that the dose is adjusted according to colony strength. Dr. Eric Mussen stated (2008 Conf) that one must not under dose, but that any overdose may harm the bees, and would be a waste of money. Fumagilin-B isn’t cheap–you can save money by giving only the appropriate amount for the colony (e.g., a 2-story colony with only 8 frames of bees only requires 1 gallon of syrup in the fall).

The Canadian label states that in springtime, if colonies are too sick to take syrup, they may be sprayed repeatedly with fumagillin in light syrup. This recommendation has been used by some beekeepers as an alternative method to feeding gallons of heavy syrup when impractical, such as when:

1. Fall colonies are plugged out with honey

2. During spring or summer nectar flows when bees won’t take syrup

3. When one is trying to avoid contaminating a honey crop with the drug.

A tweak that they made was to make the concentration stronger, and dribble a soup can full (“cup ‘o soup”) of treated syrup per colony over the bees. The Canadian label suggests 2g per liter, or about double strength. There has been considerable debate as to whether that strength is best.

So, let’s do the math! The approved 2-gallon dose of a solution of 454g of Fumagilin-B (at 21mg a.i./g) per 100 gal of syrup gives a 190mg dose of active ingredient to a strong colony. There are 32 cups in two gallons (a nearly-full soup can holds about a cup). Therefore, a one-cup drench of double strength would apply less than 12mg of active ingredient, and even if repeated three times at weekly intervals, would total less than 36mg total—5x too weak! Most other effective scientifically tested alternative applications have been in the range of 30mg – 100mg active ingredient per dose, repeated 3 – 4 times (Higes 2006, Wyborn 1986).


Update June 2015: The “strong drench” for nosema.  Some beekeepers mix one 454 g bottle of Fumagilin B into 7 gallons of syrup, and then drench each hive with 8 oz of the solution.  There are 9534 mg of active ingredient in a 454 g bottle.  There are 112 8-oz cups in 7 gallons.  That works out to 85 mg a.i. per drench (or about 3x the field-proven rate of 30 mg per week).

Since the frantic efforts to control N. ceranae back when CCD was hitting us hard, some of those beekeepers who swore by the strong drench don’t bother with nosema any more.

For best bee health, I’d first focus upon good protein nutrition and varroa control.  If you suspect that nosema is a problem, I’d definitely check out a number of samples with a ‘scope before you spend money on fumagillin (one beekeeper recently spent tens of thousands of dollars on the product before bothering to send me some samples of his sick bees–nosema was only present in one sample out of seven, and at low level).


I am in no way suggesting that anyone mess with label recommendations, but it seems to me that if you want to apply 2 gallons worth of active ingredient in three cupfuls, applied a cup at a time over three weeks, that the concentration would need to be 32 times as strong, divided by three, or about 10x concentration, in order to achieve the recommended dose of active ingredient. I’ve heard of beekeepers mixing it 15 times as strong, and applying two doses, but now we’re getting into the problem of not applying continuous treatment for the one-month duration (based upon the time for a brood cycle, and the expected life of adult bees, a month seems barely adequate).

Note that both Higes and Pernal (2008 Conf) report that bees don’t like the taste of concentrated fumagillin. The question arises as to whether they will ingest enough of a high-strength dribble. As usual, we need more research. At least one scientist has already tested the efficacy of the strong drench (pers comm), and I am currently testing it in my CSBA-funded trial.

The critical thing to remember is that the colony must receive a sustained dose, since fumagillin doesn’t kill the spores. The colony must either receive gallon quantities that are consumed over time, or multiple dosages a week apart. Note that Higes didn’t achieve full control until after four treatments! Also remember that weaker colonies require less syrup than stronger colonies, since there are fewer bees. It is a waste of money to give a 4-frame colony an 8-frame dose.

It may be that some of those suggesting stronger dosages are on the right track, although authorities I’ve spoken with are quick to caution not to mess with the labeled rate (including Dr. Mussen, whose opinion I greatly respect).

The issue of treatment cost is clearly on commercial beekeepers’ minds. At today’s prices, the recommended fall treatment of two gallons of Fumagilin-B syrup would cost nearly nine bucks a colony (ProSweet at 30¢ a lb, and $2.64 for the drug) not counting labor! The syrup cost would not apply if one were feeding anyway, but would count if the bees already were heavy with natural stores. You can’t cut the drug cost, since you need to apply the same amount of active ingredient, no matter how applied, but you may be able to cut the syrup cost used for delivery. Again, some form of syrup as the carrier is likely the best, since syrup is rapidly distributed to all members of the colony through the process of food sharing (trophallaxis).

We can probably forget some of what we’ve learned about successfully treating for N. apis, since that species is actually getting difficult to find. Fumagillin treatment for apis focused on treating the colonies when they were exposed to fresh bee poop in the fall, or to residual spore-containing feces during cell cleaning during spring brood expansion. Those recommendations may no longer apply, since the main transmission route for N. ceranae spores may be through stored pollen. I’m sure that we’ll be hearing revised recommendations as researchers focus on the new species. One speaker at the Conference stated that “researchers will know much more about treatments in 18 months to two years”–an agonizingly long time for beekeepers wanting answers in order to keep their businesses afloat!

Fumagillin may have to be used repeatedly over a period of two to three years in order to allow the bees to really clean the combs of spores. On the other hand, fumagillin is an antibiotic (or antifungal), and as such may affect the bees adversely by upsetting the gut flora, or due to other undetermined side effects. However, data from 21-day feeding trials (Anon 1986) do not indicate any adverse effects as far as bee mortality or in broodrearing. If nosema is prevalent, the benefit of treatment has clearly been shown to outweigh any harm. Generally, treatment with fumagillin is indicated only if testing indicates an elevated spore count (above 1 million spores per bee for N. apis; data is lacking for N. ceranae, but the provisional threshold may likely be lower). In my research on fumagillin, I also get hints that it may sometimes have a negative affect upon colony wintering, although Szabo (1987b) found no indication of such.

From a cost-benefit aspect, Dr. Frank Eischen’s recent feeding trial in California(2008 Conf) demonstrated that at low infection levels, simply feeding pollen supplement may result in better colonies for almond pollination, than by treating with fumagillin. That is, the dollars that you’d spend for prophylactic treatment with fumagillin may be better invested in pollen supplement. We need further research and field experience to determine whether the progression of the disease in the following season warrants prophylactic treatment.

Fumagillin has been successfully used to control nosema since 1957. Although we have seen no sign of resistance to by N. apis yet, other species of nosema problematic in insect culture have become completely resistant to the drug (Idris 2001). Therefore, it would be wise to explore alternatives. This would allow us to rotate treatments in order to avoid the development of drug-resistant nosema.

I apologize if you feel confused by my discussion (and thinking out loud) of issues regarding treatment with fumagillin. To play it safe, consult your state apiculturist, or just stick to the label until researchers adjust their recommendations.

UPDATE 5/08/2008

I am currently analyzing my winter treatment trial, and have started a summer treatment trial.

Surprisingly, colonies with moderate spore counts (~1M spores/bee) are thriving this spring, and building up well and throwing (infected) swarms!

Re alternative application of Fumagilin-B, the key thing appears to be to get 30mg active ingredient into a colony each week, repeated for 4 weeks. That works out to the following dilutions and amount applied.

454g bottle/40 gal syrup =30mg/pt

454g bottle /20gal syrup = 30mg/cup drench

454g bottle /10gal syrup = 30mg/half cup drench

Update–see “A trial of the drench method”

Note that the product is not very stable in syrup, and should be used quickly! Dr. Eric Mussen asked Medivet about solution stability:

The active ingredient in solution can lose
20-30% of its activity in about four weeks of
storage. With significantly longer storage,
the activity will drop to 50% or less. The
company states that the potency will not
diminish nearly that quickly, if the bees have
taken up the syrup, processed, and stored it.

Next installment

Alternative treatments to fumagillin, management techniques to minimize infections, and comb disinfection options. Due to the urgency of this information, editor Joe Graham is generously allowing me to post articles to my website prior to publication. Please check www.scientificbeekeeping.com. I also hope to have posted a preview of a trial that I am performing to test the efficacy of HoneySuperCell® combs against varroa.


I would like to thank Drs. Eric Mussen, Raquel Martín-Hernández, Aránzazu Meana, Mariano Higes (and others) for taking the time to fill in details on nosema to me. I greatly appreciate the help of library wizard Peter Borst. I’d especially like to tip my hat to Dennis Van Engelsdorp, Drs. Jerry Bromenshenk, Jeff Pettis, Diana Cox-Foster, and their teams, for the painstaking research they have done towards understanding colony health and disease.


Anon (1986) Report on 21-day experimental feeding of Fumagillin DCH Pulvis to honey bee colonies in the spring season. Station for the Protection of Nature and Wildlife, 7136 Facankert.

CHC (2005) Fumagillin: Its manufacture and use. http://www.honeycouncil.ca/users/folder.asp?FolderID=5224

Cox-Foster, and others too numerous to mention (2007) A metagenomic survey of microbes in honey bee colony collapse disorder. Science 318(5848): 283-287.

Cummins, J (2007) Parasitic Fungus and Honeybee Decline http://www.i-sis.org.uk/PFHB.php

Furgala, B & TA Gochnauer (1969) Chemotherapy of nosema disease. ABJ 109: 218-219.

Higes M, Martín-Hernández R, Garrido-Bailón E, Meana A (2006) An approach to Nosema ceranae control with fumagillin in field conditions Effects of natural compounds on Nosema diseased honeybees in laboratory conditions. Proceedings of the Second European Conference of Apidology EurBee Prague (Czech Republic) 10-16 September 2006

Idris, A.B.1, Zainal-Abidin, B.A.H.2, Sajap, A.S.3, Noran, A.M.2 and Hussan, A.K. (2001) Some studies on Nosema infecting DBM in Malaysia. http://www.regional.org.au/au/esa/2001/10/1005idris.htm#TopOfPage

Kochansky, J and M. Nasr (2003) Laboratory studies on the photostability of fumagillin, the active ingredient of Fumidil B. Apidologie 35 (2004) 301-310

Moffet, J. O., J. J. Lackett, and J. D. Hitchcock. 1969. Compounds tested for control of Nosema disease in honey bees. J. Econ. Entomol. 62: 886-889.

Pernal, S.F., Pettis, J. and A. P. Melathopoulos (2008) A preliminary evaluation of control methods for Nosema apis and Nosema ceranae. American Bee Journal 148: in press.

Szabo, TI and DT Heikel (1987a) Effect of Fumagillin Treatment on Nosema Infection, Survival and Populations of Overwintering Honeybee Colonies. J. Apic. Res.26(3): 186-190.

Szabo, T & DT Heikel (1987b) Effect of dry fumagillin feeding on spring nosema spore counts in overwintered colonies. ABJ 127: 210-211.

Wyborth, MH, & DM McCutcheon (1987) A comparison of dry and wet fumagillin treatments for spring nosema disease suppression of overwintered colonies. ABJ 127: 207-209.