Oxalic Acid Sublimation Treatment

An experiment to determine its effectiveness
Dennis Clemens D&WBKA

This was a small scale local comparison of the levels of varroa mites found in 22 hives after 0,1 or 2 treatments.

The thinking behind the project.

In the past, my annual treatment regimen was as follows:

January, week one – each colony treated once with oxalic acid dihydrate sublimation.
June , week one – spring flow supers removed and each colony treated with MAQS (formic acid).
August – main flow supers removed and each colony treated three times with a 10 day thymol based product.

Definitely an Integrated Pest Management routine using a belt and braces approach which worked for me!

However an article in the BBKA News (December 2018, page 403 “The Apiary in December” by Lynfa Davies) made reference to a piece of research by the Laboratory of Apiculture and Social Insects (LASI) at Sussex University, which indicated that oxalic acid was more effective as a sublimation treatment (97.6% of the mites killed) than the trickle method (93% mites killed). They went on to discover that if a second sublimation treatment was given a fortnight later the kill rate rose to nearly 100% and that the mite levels remained at a controlled level for more than a year. The full report is available here.

If this proves to be the case then the savings to the beekeeper( (pence per treatment instead of pounds) and benefits to the bees (fewer chemicals being introduced throughout the year) would be considerable, not to mention the reduce risk of tainted or contaminated honey.

This got me thinking- there should be a correlation between treatments and subsequent mite levels. ot being one to blindly accept the pronouncements of others, I decided to conduct an experiment of my own, the results of which would either support the research or give cause to question it.

In order to ensure the methodology and the results should be independently verified and to avoid any unwitting skewing of the the results arising from my own expectations, I recruited some willing helpers from the ranks of the Dorchester And Weymouth Beekeepers Association (D&WBKA) and organised them into teams. I randomly selected one hive from each of the five apiaries as a conrtol group and gave them no sublimation treatment; 5 hives from across 4 apiaries were given one sublimation treatment during the last week if December; 12 hives from across 5 apiaries were given two treatments during the last week of December and again, a fortnight later, during the second week of January. None of the hives were checked to determine if they were broodless or not.

Subsequently, in April 2019, the hives were revisited by different teams who did not know how many treatments the hives had ben given. By using a combination of drone uncapping (about 50 at the pink-eye stage from each hive) and sugar rolling (about 200 adult bees from each hive) a record of the number of mites found by each method in each hive was compiled. The records were handed back to me and I then passed them on to a bee keeping colleague who, being more computer savvy than myself, was able to process the information and produce the table and bar graph shown below. I think the results speak for themselves!

I am extremely grateful to all those members of the D&WBKA who so generously gave their time to commit help with this project (they even found and marked a few queens for me while they were at it – how jammy am I?).

I will continue to monitor for mites later in the year since drift of the drones from other sites, or colony failures nearby or even weak feral colonies could result in my bees harvesting stores ( and mites) and reinfesting themselves.

Please note that oxalic acid dihydrate is a dangerous subbstance if not handled according to the instruction which come with it. Always the correct Personal Protective Equipment.

Comparison of levels of Varroa mites found on bees after 0,1 and 2 treatments with oxalic acid dihydrate

Description 0 Treatments
5 hives
1 Treatment
5 hives
2 Treatments
12 hives
Varroa on ~50
pink-eyed drone pupae.
7 per hive
2.4 per hive
0.75 per hive
Varroa on ~200
rolled adult bees.
3.6 per hive
1 per hive
0.5 per hive