Hey everyone! I hope you are having a fantastic week. I wrote todays blog about fumagillin, an antimicrobial agent beekeepers use to treat nosema. Most beekeepers (at least commercial that is) use fumagillin to treat their colonies once or twice a year. However this will likely change this year because Medivet, the only manufacturer of fumagillin, is discontinuing its production. I think this impacts commercial beekeepers more than hobbyist and sideline beekeepers because these smaller beekeepers typically do not treat for nosema with fumagillin anyway. But many commercial beekeepers do, and now these beekeeper will either be forced to stop treatment or find an alternative. For most commercial beekeepers, nosema is one of their top 3 concerns behind varroa and forage depletion. Nosema is such a concern, especially before colonies enter overwintering sheds, that I predict certain beekeepers will use unusual practices to treat nosema, i.e. feeding colonies bleach to control for chalkbrood. But before I see alternative treatment methods, I wanted to see just how effective fumagillin was so I can relay this information to commercial beekeepers. I talked to industry leaders, many of whom say fumagillin is not effective against Nosema ceranae anyway. So fumagillin may have been a costly, yet useless treatment for many years. But I wanted to look into this myself. To do so, I reviewed a paper call “Does fumagillin control the recently detected invasive parasite Nosema ceranae in western honey bees (Apis mellifera)?”. The paper was published nearly 10 years ago, but is still very relevant. I went into this blog with certain questions, which I will attempt to answer as the blog progresses.
1)How effective is fumagillin at controlling nosema?
2)Are nosema treatments even necessary?
3) With the recent discontinuation of fumagillin, what will (or should) beekeepers turn to?
Nosema is a a fungal disease that affects adult bees. More specifically, Nosema is a single-celled microsporidian that lives in the gut of bees. Nosema spores are transferred between colony members by their feces, discharged waste matter that includes many nosema spores. Additionally, nosema spores can be transferred by non-infected colony members by trophallaxis or infected brood food consumption. Once ingested, these spores enter the cells lining the gut. These cells digest and absorb nutrients ingested by the bees, so these cells are a necessary part of the digestive system. Once in the cell, nosema spores begin a fast and furious replication process. The replication continues until the cell can not longer hold spores, in which time the cell bursts and is destroyed. Once enough cells become destroyed, the bee digestive system becomes permanently impaired. Infected bees often cannot digest pollen, which shortens the life of the bees.
Nosema has no observable symptoms, which make nosema difficult to understand, prevent, or even treat. I have read that adult bee symptoms can include disjointed wings, distended abdomen, absence of stinging reflex, and dysentery, but I have not seen a correlation between these symptoms and high nosema levels. Because nosema has no observable signs, many commercial beekeepers choose to treat their entire operation. Typically, beekeepers treat colonies with fumagillin, an anti-microbial agent long believed to treat nosema. Beekeepers admix fumagillin with sugar syrup, and supplement colonies in both early spring and late fall. Unlike varroa, nosema cannot be easily monitored so beekeepers choose to treat their entire operation, which is costly. Each treatment costs $2.36/colony, which can add up if a beekeeper is treating 1000’s of colonies twice a year.
Fumagillin is a common management practice for beekeepers, which has spurred research on its effectiveness. However, this research has revealed mixed results. Research suggests that fumagillin is not effective against Nosema ceranae, a new species that has nearly displaced Nosema apis. In fact, Huang et al. 2013 demonstrated that colonies fed fumagillin actually had higher levels of Nosema ceranae than colonies not fed at all. This fact is corroborated by other studies, which suggest that treating colonies with fumagillin is not effective anyway (Williams et al. 2011; Goblirsch 2017). Regardless, many beekeepers have continued to use fumagillin because: 1)they believe a spring treatment increases honey production, 2) many beekeepers believe nosema can proliferate during overwintering storage, so a fall nosema treatment is necessary, and 3) to receive government funding for high colony losses, beekeepers must show they manage nosema levels in their operation. So despite the lack of evidence, beekeepers continue to use fumagillin for many different reasons.
Researchers have not seen evidence that fumagillin treatment increases honey production, decreases nosema proliferation during storage, or even the lowers nosema levels in general. But I understand why beekeepers do treat. Beekeepers livelihoods are based upon the productivity of their colonies, so why not be cautious and treat. Unlike varroa, nosema is naked to the human eye, so there is now way of knowing its impact on colony health. To avoid the risk, beekeepers take the financial hit to avoid catastrophic losses from an unobservable disease.
In June, Medivet will discontinue production of fumagillin. Medivet is the only producer of fumagillin, so beekeepers will need to find a replacement or decide not to treat at all. I decided to look into the effectiveness of fumagillin so I can better consult beekeepers. I found a study that measured the effect of fumagillin on Nosema ceranae. I liked this study because they looked at spring fumagillin treatment, then followed colonies throughout the year. They were interested in whether a spring fumagillin treatment lowered nosema levels, and then kept these levels low throughout the year.
Researchers found that a spring fumagillin treatment did lower nosema infestation, however the summer nosema levels were indistinguishable between the spring treatment and non-treatment control. This study suggests a few things: 1)nosema levels seem to go through seasonal cycles, despite treatment or no treatment, 2)fumagillin did lower nosema levels for this study and 3) infected colonies can recover during the summer, without a treatment. Infected colonies did eventually recover, despite having high levels of nosema in the spring. Because of this recovery, a fumagillin treatment seems pointless, unless higher spring nosema levels impede honey production or decreases colony health. But I have not seen evidence that suggests this.
I think nosema levels cycle throughout the season, regardless of a treatment. Below is a graphic using data from the Bee Informed Partnership, and presented by Ben Sallman. The graphic compares beekeepers across the country that either treat with fumagillin or do not. As you can see from the graphic, nosema levels go through seasonal cycles, regardless of a treatment.
Thus, seasonal cycles are expected. As you can see in the figure above, we do see seasonal cycles for nosema spore count, even for colonies treated with fumagillin. Nosema levels rise high in the spring, dip in the summer, and begin to rise again in the fall. Nosema may be high in the spring for a two reasons:
1)Spring buildup is a very stressful time. The queen is laying like crazy. The colony contains a lot of brood, yet not enough nurse bees to take care of it all. This is why I also see a lot of European Foulbrood in the spring.
2) Colonies are building as forage is lacking in certain areas. A heavy honey flow does not come to Minnesota until mid-may and early-June in North Dakota. Once the heavy flow begins, I typically see nosema disappear.
Fall has high nosema levels for similar reasons:
1)The colony becomes stressed in the fall as summer bees convert to winter bees and the colony prepares for overwintering. Oftentimes, varroa levels are highest in the spring, bees population declines, forage decreases, and the weather turns. Also, bees are not flying nearly as often. These are all stressors that may increase nosema levels.
2)Bees are not flying nearly as often and the colony is converting to winter bees. Winter bees are not flying and purging their guts nearly as much as summer bees, so one would expect higher nosema levels.
So, should beekeepers find a fumagillin alternative? I would be ignorant to say no, because nosema is still a mystery. Although some studies suggest fumagillin is ineffective, nosema may impact colony health more than we expect. The summarized study suggests a fumagillin treatment did lower spring nosema levels, but a spring treatment did not impact fall nosema levels. So, what type of impact did these high nosema levels have? Did the colonies produce less honey? Did the colonies become weaker? We do not know, but if they did, beekeepers may want to treat so they have higher producing colonies. For a hobbyist, it is easier to not treat. However, commercial beekeepers are in a tougher predicament. Treat nosema for $2.36/colony, or not treat and risk losing money in lower colony production. This is a real life case study BIP will be monitoring. We have monitored colonies treated with fumagillin for many years, so once this treatment suddenly ceases, we can hopefully provide useful insight. I have talked to several beekeepers, and they have decided to feed their bees either acetic acid, oxalic acid, or nosevit. I am sure other alternatives will be used, but these are what I currently know. But I expect colonies to do well, be just as productive, and save beekeepers thousands of dollars per year.
Thank you very much! This is the Daily Guide to Beekeeping. If you liked it or had any thoughts, please comment or email me at email@example.com. Please subscribe to the blog to receive daily alerts. Follow the blog on twitter @dailyguideto and our facebook page at The Daily Guide to Beekeeping.
Goblirsch, M. Nosema ceranae disease of the honey bee (Apis mellifera). Apidologie, 1-20.
Huang, W. F., Solter, L. F., Yau, P. M., & Imai, B. S. (2013). Nosema ceranae escapes fumagillin control in honey bees. PLoS pathogens, 9(3), e1003185.
Williams, G. R., Sampson, M. A., Shutler, D., & Rogers, R. E. (2008). Does fumagillin control the recently detected invasive parasite Nosema ceranae in western honey bees (Apis mellifera)?. Journal of invertebrate pathology, 99(3), 342-344.
Williams, G. R., Shutler, D., Little, C. M., Burgher-Maclellan, K. L., & Rogers, R. E. (2010). The microsporidian Nosema ceranae, the antibiotic Fumagilin-B®, and western honey bee (Apis mellifera) colony strength. Apidologie.