Nosema in NZ Hives: The Two Types and how to keep them in check
Nosema is one of those problems that rarely announces itself. There is no obvious chewed brood or mite you can spot on a sticky board — just colonies that dwindle, build slowly out of winter, or quietly fail.
The two types of Nosema
There are two species that infect honey bees, and both occur in New Zealand:
- Nosema apis — the long-known type. It is the classic cold-climate, late-winter and spring parasite, and is the one most associated with visible dysentery.
- Nosema ceranae — originally a parasite of the Asian honey bee, Apis cerana. It tends to be more “silent”, with no obvious dysentery, just steady colony decline.
Key visual and symptomatic differences
For field identification, symptoms can vary depending on which type has infected the hive.
| Feature / Symptom | Nosema apis | Nosema ceranae |
|---|---|---|
| Dysentery / fecal staining | Prominent on the hive exterior and top bars. | Rare or completely absent. |
| Bees crawling at hive entrance | Common; flightless bees with swollen abdomens. | Rare; infected bees often die away from the hive while foraging. |
| Impact on colony | Slower population decline and higher winter losses. | Rapid adult bee mortality, which can lead to sudden colony collapse. |
With our wet, drawn-out springs, it is important to understand what Nosema actually is, the two forms we deal with, and what genuinely helps.
What is Nosema?
Nosema is a microsporidian — a single-celled, spore-forming parasite that sits within the fungal kingdom. It can only reproduce inside a living host cell.
A bee picks it up by ingesting spores from contaminated comb, stores, water, or while cleaning the hive.
Once swallowed, the spore fires a tiny harpoon-like polar filament into the cells lining the bee’s midgut, also called the ventriculus, and injects its contents. It then hijacks those gut cells to replicate, eventually rupturing them and shedding fresh spores back into the gut.
The damage is to the bee’s ability to digest food and absorb nutrients. Infected bees burn through their reserves, age prematurely, produce less brood food, and die younger.
At colony scale, that shows up as slow spring build-up, dwindling populations, and overwintering losses.
Nosema is best understood as a stress disease. It does its real damage in colonies already under pressure from poor nutrition, varroa, viruses, or a long confining winter.
Recommended solutions
There is no single silver bullet, and chemical options are limited. Management is mostly about reducing the stressors that allow Nosema to take hold.
1. Strong nutrition
Well-fed colonies tolerate infection far better. Going into and out of a wet spring, make sure bees have adequate pollen, protein, and stores.
2. Keep varroa down
Varroa and the viruses it spreads are the biggest single stressor on a colony. Good mite control is also good Nosema management.
3. Young queens and strong stocks
Requeening helps keep colonies populous and resilient. Some bee lines may also tolerate Nosema better than others.
4. Comb and hygiene
Spores can persist in old comb and stores. Rotating out old brood comb and avoiding the movement of frames between sick and healthy hives helps reduce the spore load that re-infects bees.
5. Dry, well-sited, well-ventilated hives
Damp conditions and prolonged confinement — exactly what a wet New Zealand spring can deliver — will favour Nosema, especially Nosema apis dysentery.
Oxalic acid vaporization and Nosema
Most beekeepers vaporize oxalic acid for varroa. There is also a growing case that it may help with Nosema.
One of the strongest pieces of published evidence is Nanetti et al. 2015, Effect of oxalic acid on Nosema ceranae infection. The authors concluded that oxalic acid can be used to help control Nosema ceranae.
Several other studies have also explored oxalic acid and related treatments against Nosema.
On top of that, the field picture in New Zealand is striking. Commercial operations that vaporize extensively through late autumn, winter, and early spring consistently report lower hive losses than those that do not.
Thorough oxalic acid vaporization across late autumn to early spring earns its place in a strong hive-health program. There is also reasonable evidence it may help with Nosema as well as varroa.
References and further reading
- Randy Oliver — Sick Bees Part 14: An Update on the “Nosema Cousins”, ScientificBeekeeping.com: scientificbeekeeping.com/sick-bees-part-14
- Nanetti A. et al. 2015 — Effect of oxalic acid on Nosema ceranae infection, Research in Veterinary Science 102:167–172.
- Tokarev Y.S. et al. 2020 — A formal redefinition of the genera Nosema and Vairimorpha, Journal of Invertebrate Pathology 169:107279.
- Scientific Advances in Controlling Nosema ceranae Infections in Honey Bees, Frontiers in Veterinary Science.
- Further oxalic acid / OAV references: Springer 2024, PMC6428737, and MDPI Applied Sciences.