Until very recently, the use of oxalic acid in apiary industry in the USA was forbidden. However, on November 14, 2014 the United States Department of Agriculture (USDA), applied for the admission of oxalic acid in the apiary industry for use as a pesticide against varroa.

The application for admission was submitted by the Environmental Protection Agency (EPA). This was done after Amitraz was readmitted in 2013 for a period of 2 years and that the results of the USDA's own research conclusively established that Amitraz has extremely adverse effects on queen bees. The registration proposal for oxalic acid stated that 24 months are normally required to reach an admission decision. In that case, it would not be permitted to use oxalic acid for bee colony treatments before 8 December 2016. But because of a presidential decree, that period was shortened. On March 10th, 2015 the EPA decided to allow the use of oxalic acid in the apiary industry.

Fewer bee colonies lost with oxalic acid

According to the monitoring data, several hundred beekeepers in the USA use oxalic acid. Beekeepers could reduce the annual mortality of their bees in 2013-2014 by more than 40% by administering oxalic acid (in 2012-2013 that was 34%). According to the same monitoring, oxalic acid is thus slightly less effective than Amitraz (47% respectively 44%). By administering either oxalic acid or Amitraz, in the USA, the total annual mortality in both years was nevertheless still at the level of 20% – 30%.

How does oxalic acid work

The admission document indicates that the working of oxalic acid in combating varroa is “not fully to totally not understood”. The brochure ‘Effectieve bestrijding van varroa’ [Effective Varroa control] (Wageningen University, 2010) states that it is not exactly known how oxalic acid works. According to the authors of this brochure, it is probable that the mites die through direct exposure because of the high acidity level, just as with formic acid.

It should also be noted that the exact working of Amitraz is also not fully understood (see https://science-in-water.com/bijen/info-over-ijzertoediening/94-virussen.html).

Bacterial problem

From the fact that oxalic acid is an anti-bacterial treatment we can deduce that when a beekeeper administers oxalic acid to his bee colonies, he is in fact attempting to get the bacterial problem under control, with the reduction of the numbers of varroa mites being a side effect.

The fundamental working of oxalic acid gives us some clues to help solve the problems facing the apiary industry in many countries.

Oxalic acid registration

Oxalic acid was first registered in the USA in 1957 as a disinfectant. In 1992 the substance became eligible for reregistration. Oxalic acid hasn't been registered for any usages in the USA since 1994.

Registration as a treatment for varroa

According to the current application document, oxalic acid treatment would reduce the number of mites by 90 to 99%. This is only valid for tests conducted under controlled conditions. There are dozens scientific publications which show similar results.

However, if the number of varroa mites is taken as the criterion, a pseudo-outcome measure is used. It would be better to take the compound outcome measure. Such an outcome is the total result. The compound outcome measure takes account of the effect of the treatment on mortality as well as on the strength of the bee colonies after the winter, the loss of queens (including the unnoticed accession of a new queen bee) and the willingness of beekeepers to use the treatment.

Hazards for the user

The EPA has classified oxalic acid in toxicity class 1, in other words in the category with the highest degree of toxicity, particularly when inhaled and for the eyes and skin.

We have established that many beekeepers, and novice beekeepers in particular, are not keen on using such aggressive treatments such as formic acid and oxalic acid. So we see that these treatments are not widely accepted, also the fact that many beekeepers work on the principle that bee colonies should not be disturbed in the winter, forms an additional bottleneck.

Crowd sourcing

Based on our own experiences we believe that the authorities in the USA have conducted sound work to assess the application for authorization of oxalic acid for use in the apiary industry. As part of the admission procedure, the EPA decided to involve the interested parties. They did this by opening a website between February 4th and March 6th 2015 where people could comment and add information. A total of 256 responses were received. In this way, everyone had the opportunity to give their opinion on the matter.

Government initiative

The fact that a government institution has taken the initiative to register a product itself can be considered remarkable. For the time being, the EPA does not see any objection to registering oxalic acid. The EPA has mainly based its decision on the admission authorities in Canada, and sees no reason to request specific data. As a result, the whole procedure has not cost as much as the registration of Amitraz (approximately $ 1 million).

Now that oxalic acid is registered, this doesn't mean to say that the problems in the American apiary industry have been solved.

Oxalic acid: not a harmless ‘natural’ treatment for bees

During our trials we observed some noteworthy effects when Ferro-Bee® was administered in combination with formic acid. Something similar was reported to us with the use of thymol. Thymol, we have discovered, also has an entirely different effect than that officially promoted. This could mean that oxalic acid also has a number of unknown effects on bees and bee colonies. It is well worth remembering that every product a beekeeper uses will always have multiple effects, interactions with other treatments and will rarely work for 100%.