Nosema Disease, Varroa Mites, and Sustainable Agriculture

So, why am I trying to breed better bees?

Losses in managed honey bee colonies have increased in recent years with a phenomenon called Colony Collapse Disorder (CCD). It has become a consensus that multiple causes are responsible for CCD events and many of those causes are related to issues with the parasitic varroa mite and a gut parasite called Nosema. These problems are not new, but several other confounding factors may be, and these together have lead to a general decline in honey bees irregardless of specific losses where the symptoms have matched CCD events. With this understanding, it is now more appropriate to address bee decline in general, as opposed to CCD.

Mite resistant bees

Here is a drone honey bee that died from Deformed Wing Virus (DWV) before it emerged from its brood cell. Varroa mites transfer DWV virus. You can see the resulting shriveled wings from the virus.

One way to improve honey bees ability to handle factors in bee decline, is to breed bees resistant to mites. Over the last several decades, major advances have occurred in breeding bees to be resistant to varroa mites by selecting for hygienic behavior. Hygienic, mite resistant bees are being propagated and distributed through many bee breeding programs including the USDA-ARS Varroa Sensitive Hygiene (VSH) bees. However, few of these programs have incorporated selection for nosema disease resistance in parallel to mite resistance.

In addition, bees produced in these programs may be adapted to their specific location or conditions not shared by all beekeepers. I may be able to better adapt the bees I use by selecting within my own environmental and management constraints. “Locally adapted bees” is a concept with renewed interest in today’s challenging beekeeping environment, yet this concept has been appreciated for some time as identified by Brother Adam in Beekeeping at Buckfast Abbey.

Nosema disease

Nosema disease can prevent colonies from growing strong. Here is a weak colony in spring.

Nosema disease is caused by two species of microsporidia, Nosema apis and Nosema ceranae. These unicellular organisms reproduce inside adult honey bees negatively affecting the mid-gut epithelium, hypopharyngeal glands, corpora allata (juvenile hormone), as well as oocytes in queens (see Huang’s article). Nosema infected bees have a shorter lifespan, dysentery, nutrition digestion problems, cannot produce essential hormones correctly, and in many ways cannot function to maintain productive or surviving colonies. The microsporidia produce spores in infected bees and after defecation, these spores are picked up by un-infected bees to continue the disease cycle. Nosema disease is normally controlled by feeding the antibiotic fumagillin dissolved in syrup during spring and fall.

Breeding for disease resistance and increased production should hopefully result in fewer colonies like this one in spring. A colony that has not grown more than this by March in Tennessee is not worth trying to revive.

Treatment is normally done without prior sampling to determine if Nosema spore levels are high enough to warrant treatment. In the past, there was a single species involved, Nosema apis. Now, a new Nosema species in U.S. honey bees, Nosema ceranae, causes much more problems than previously observed. This may explain why nosema disease resistance has not already been incorporated into many large scale, historic breeding programs.

Spore sampling for Nosema requires microscopic examination of bee samples and could possibly be used as a selection measure. With the exception of formal bee breeding programs, many beekeepers raise queens from colonies that seem to do well as compared to other colonies. Specific measures are often not incorporated, likely due to the time involved in sampling.

Nosema disease is an impediment to Organic Production and Certified Naturally Grown honey bees.

Formal recommendations by the National Organic Standards Board to the National Organic Program in 2010 point out that antibiotics are not permitted for any type of livestock (see .pdf). It is unlikely the antibiotic fumagillin will ever be included as an allowed organic substance. Fumagillin is also prohibited for use in Certified Naturally Grown production. There are numerous essential oils on the market for control of nosema disease, however none of these have been shown to work. More sustainable than using annual, preventative treatments, would be if the bees could normally handle this disease on their own. There is some evidence that resistance to Nosema by honey bees is a heritable trait and therefore breeding for that trait may be effective in reducing or eliminating prophylactic nosema treatments.