Cleaning up after a Nosema apis outbreak is no easy chore. Your best course of action is to prevent an infection in the first place. My second piece of advice is to make sure it actually is Nosema apis that you are trying to clean up. It is easy to confuse simple honey bee dysentery with Nosema apis, so you will want a positive identification before you start. Identification requires a microscope and some training, or you can ship your sample to a lab.
Both Nosema apis and Nosema ceranae are transmitted by resistant spores that can survive long periods. The disease is transmitted when honey bees ingest the spores. This can happen when bees are cleaning the combs or other parts of the hive.
Since Nosema apis usually causes dysentery-like symptoms such as distended abdomens and defecation in the hive, it can be confused with normal wintertime honey bee dysentery which also causes distended abdomens and defecation in the hive. But with Nosema apis the spores pass through the digestive tract along with the feces. When other bees try to clean up the mess, they become infected as well.
Hive bodies, bottom boards, inner covers or any other wooden parts of the hive can be fumigated with various chemicals—such as glacial acetic acid—or they can be scorched with a blowtorch. It is best to first scrape all the wooden surfaces to get the thick stuff off, then scorch your woodenware and your hive tools with the torch.
A number of different chemicals can be used to fumigate combs, but none are very practical for the hobby beekeeper. They can also be irradiated or treated with ozone—also impractical and expensive if you have just a few hives. The simplest way to disinfect is with heat, but that isn’t easy either. Randy Oliver pieced together the following data that he found in a variety of research papers. The table shows time and temperature needed to disinfect Nosema-infected combs with heat.
|Degrees F||Degrees C||Time|
Beeswax will melt at about 145°F (63°C), so if you decided to use high heat, you need a way to monitor and control it. As with your woodenware, I recommend that you first scrape the frames to get off as much residue as possible before you treat with heat.
All in all, prevention is far easier than trying to clean up. The best defense against Nosema or any other bee disease is to maintain populous healthy hives.
- Maintain large colonies going into winter. Combine small colonies with larger ones as long as they are all healthy.
- Provide good ventilation so hives stay dry inside.
- Ensure that colonies have adequate supplies of both honey and pollen going into winter.
- Keep hives in a sunny winter location to encourage cleansing flights.
- Treat for Varroa mites. Bees weakened by mites are more susceptible to a variety of diseases.
- Continually replace old combs with new ones to prevent disease build-up.
If you believe your bees have Nosema or you want to prevent an infection from spreading, you can treat your colonies with fumagillin according to the package directions. Fumagillin is an antimicrobial agent isolated from the fungus Aspergillus fumigatus. The fungus is found naturally in soil and decaying organic matter. Fumagillin is sold under the brand name Fumidil-B or Fumagilin-B and is fed to honey bees in syrup. Fumagillin prevents the Nosema spores from reproducing in the honey bee gut, but it is unable to kill the spores.