Oxalic Acid helps fight Nosema!

What the Research Shows About Protecting Your Hives

Updated for New Zealand beekeepers — science-backed, practical guidance.

Understanding the threat: Nosema ceranae

Nosema ceranae is a gut parasite that infects the epithelial lining of a bee’s midgut, disrupting digestion and shortening lifespan. Heavy infections are linked with dwindling populations and winter losses. In many temperate regions (including NZ), N. ceranae is now the dominant Nosema species, making it an ongoing concern for many beekeepers.

A new role for an old treatment

Oxalic Acid (OA) is already a staple product for Varroa destructor control, typically used by vaporization or dribble methods. Recent research shows OA also helps to manage Nosema ceranae by reducing spore loads and improving colony survival in both laboratory and field settings [1], [3].

In one study using 0.25 M OA in sugar syrup, treated bees showed spore counts averaging 11.86 × 106 compared to 30.64 × 106 in untreated bees. When colonies were treated twice in autumn, three weeks apart, infection prevalence dropped by approximately 53% in young bees and 44% in older bees. All treated colonies overwintered successfully, while three of five untreated colonies did not [2].

How might Oxalic Acid work?

OA appears to work in two ways: by directly inactivating Nosema spores within the gut, and by altering gut conditions to make them less favourable for infection. Studies report that repeated OA applications (vaporization or syrup feeding) significantly reduce Nosema spore loads and boost colony survival relative to untreated controls [1], [3].

Microbiome Effects: Health from the inside out

A 2024 Apidologie study revealed that OA doesn’t just target pathogens — it also influences the bee gut microbiome. Colonies from urban or intensively managed areas often show “microbial dysbiosis” — reduced diversity and more pathogens. After OA treatment, these stressed colonies saw:

  • Lower loads of pathogens, including Nosema ceranae and Hafnia alvei
  • Increased levels of beneficial bacteria like Gilliamella
  • Greater overall microbial balance and resilience

What the studies agree on

  • OA reduces Nosema spore loads across multiple trials [1], [2], [3].
  • Two or more treatments spaced 2–3 weeks apart are most effective [2], [3].
  • Improved overwintering is seen in OA-treated colonies [2].
  • Microbial balance improves in stressed or dysbiotic colonies [5].

The bigger picture

From reducing Nosema spores to supporting healthy microbiota, oxalic acid is proving to be more than a varroa tool. Used at the right time and concentration, it supports hive health and resilience — especially for colonies under stress [2], [5].

References

  1. MDPI (2022): Review of OA use for Nosema ceranae control — reduced prevalence and improved colony survival. https://www.mdpi.com/2076-3417/12/2/783
  2. Higes et al. (2015): “Effect of oxalic acid on Nosema ceranae infection.” Demonstrated 0.25 M OA syrup reduced spores by 50–60% and improved overwintering. https://www.sciencedirect.com/science/article/abs/pii/S0034528815300333   (ResearchGate access)
  3. PMC6428737 (2019): Review of repurposed bee medications — oral OA (0.25 M) significantly reduced Nosema infection. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6428737/
  4. PubMed: Index of OA treatment studies for N. ceranae. https://pubmed.ncbi.nlm.nih.gov/26412538/
  5. Springer (2024): “Landscape and management drive OA effects on honeybee microbiota.” OA reduced pathogens (incl. N. ceranae) and enriched beneficial bacteria in stressed colonies. https://link.springer.com/article/10.1007/s10340-024-01829-3

Disclaimer: Always follow New Zealand regulations and product labels when using oxalic acid. Research findings are promising, but outcomes depend on colony health, environment, and timing.

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