{"id":875,"date":"2026-06-17T15:17:00","date_gmt":"2026-06-17T15:17:00","guid":{"rendered":"https:\/\/scientificbeekeeping.com\/scibee1\/?p=875"},"modified":"2026-08-18T15:32:56","modified_gmt":"2026-08-18T15:32:56","slug":"875-2","status":"publish","type":"post","link":"https:\/\/scientificbeekeeping.com\/scibee1\/875-2\/","title":{"rendered":"Testing Varroxsan: Part 1"},"content":{"rendered":"\n

Testing Varroxsan<\/strong><\/h2>\n\n\n\n

Part 1<\/strong><\/h2>\n\n\n\n

Randy Oliver<\/strong><\/h3>\n\n\n\n

ScientificBeekeeping.com<\/strong><\/h3>\n\n\n\n

First Published in ABJ in April 2026<\/h3>\n\n\n\n

I published my first article about extended-release oxalic acid (OAE) for mite control over nine years ago <\/em><\/strong>[[1]<\/a>], but it took until last year for the first registered product, VarroxSan, to finally hit the U.S. market.  So how does it compare to other extended-OA treatments?<\/em><\/strong><\/p>\n\n\n\n

I\u2019ve done a lot of research on potential treatments for varroa control, favoring \u201cnatural\u201d biopesticides that don\u2019t problematically contaminate our combs and honey (and are likely more sustainable).  Extended-release oxalic acid (OAE) stands out as one of our best options (to be used in rotation with other treatments<\/em><\/strong>).  But I leave it to others to go through the onerous and expensive registration process to bring them to market.  So I was very happy to see the registration of VarroxSan strips (and am in regular contact with two other beekeepers who are currently in the tedious registration process of additional OAE products).<\/p>\n\n\n\n

<\/a><\/a>SO HOW WELL DOES IT WORK?<\/h2>\n\n\n\n

I can find only a single published scientific field trial of VarroxSan, by Branchiccela in Uruguay [[2]<\/a>], using Africanized bees.  Their team ran three separate trials over the course of several years, each for 42 days, all in hives consisting of a single Langstroth brood box with a honey super above (additional supers in the spring trial).  In their winter trial, they tested 4 hung VarroxSan strips (the label dosage for a strong single).  For the spring trial, they also added a \u201cboosted\u201d group that received an additional 2 strips after 20 days (the boost was added since during this run the colonies nibbled the strips).  For their autumn trial they tested three different doses of VarroxSan (3, 4, or 5 strips), as well as 4 strips placed \u201cabove\u201d the broodnest (I assume that meant laid flat across the top bars of the brood box).  In all three trials they included an untreated negative Control group.<\/p>\n\n\n\n

A<\/a><\/a> Note on Mite Reduction vs. Efficacy of Treatment<\/h3>\n\n\n\n

It\u2019s easy to calculate the degree of reduction<\/em><\/strong> of the mite infestation rate by taking before and after mite wash counts, but that doesn\u2019t tell you the efficacy<\/em><\/strong> of the treatment, because it doesn\u2019t account for how much the count would have increased if you hadn\u2019t treated.  So to calculate efficacy, you need to include an untreated Control group.<\/p>\n\n\n\n

Example:<\/strong> At the \u201cnormal\u201d rate of mite reproduction, you\u2019d expect the infestation rate of an untreated non-resistant colony to double in a month.  So if a treatment only held the count steady (no reduction<\/em><\/strong>), it would still calculate out at 50% efficacy.  <\/em><\/strong>That clarified, I did a reanalysis of their data.<\/p>\n\n\n\n

They had calculated efficacies by comparing the total mite drop count during treatment to that from a post-treatment application of synthetic miticides.  But that is not how we beekeepers typically judge the result of a treatment, so from their data I recalculated efficacies (using the Henderson-Tilton equation [[3]<\/a>]), based upon the colonies\u2019 starting and ending mite wash counts (Figure x).I can find only a single published scientific field trial of VarroxSan, by Branchiccela in  Uruguay [[4]<\/a>].  They ran three trials in hives consisting of a single Langstroth brood box, with a honey super above (additional supers in the spring trial).  The trials were run for 42 days above stickyboards (counting all fallen mites), at which time flumethrin\/amitraz strips were added to kill any remaining mites.  \u201cThe difference between the remainder mites fallen during the follow-up treatment period and the dead mites fallen during the OA treatment allowed [us] to calculate the OA efficacy<\/em>.\u201d<\/p>\n\n\n\n

They also ran a fourth field experiment for three years to \u201canalyze the consequences of OA treatment in colonies with different initial infestation rates of [mites],<\/em>\u201d in total taking 293 pre- and post-treatment mite wash counts.<\/p>\n\n\n\n

<\/a>Their Conclusions<\/h3>\n\n\n\n

They concluded that: \u201c[VarroxSan\u2019s] efficacy depends on the time of the year it is applied, the dose, and the method of administration<\/em>.\u201d   They also found that there was no noticeable effect from VarroxSan treatment upon the adult or brood populations of the colonies, nor any queen losses.<\/p>\n\n\n\n

The sole conclusion that they drew from their extensive fourth study was that \u201chigher infestation levels before the experiment correlated with higher infestation levels after the OA treatment<\/em>\u201d \u2013 this stunning finding suggesting that their OA treatments didn\u2019t zero-out many mite infestations (surprising to me, since we regularly see oxalic sponges zero out the mites).<\/p>\n\n\n\n

<\/a>My Own Analysis of their Results<\/h3>\n\n\n\n

Their trials were all run in hives with relatively low infestation rates (average half-cup mite wash counts equivalents in the 3-9 mite range).  Since beekeepers typically check performance of a treatment by mite wash counts, I used a different method to calculate efficacy than they did [[5]<\/a>], based upon their before and after mite wash numbers (Figures 1 & 2).<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Fig. 1  <\/strong>Branchiccela\u2018s team ran three separate trials over the course of several years, with the winter treatment showing the highest efficacy.  For the spring treatment, due to nibbling of the strips, they added 2 additional strips at Day 20 to the \u201cboosted\u201d hives.  In autumn, they also tested three levels of doses of hung strips, as well as 4 strips applied \u201cabove the brood box\u201d (I\u2019m guessing laid flat, since they labeled the hung strips with the suffix \u201cins\u201d). Note: due to the low starting infestation rates in all trials, take the efficacy figures as ballpark approximations.<\/p>\n\n\n\n

Practical application:  The efficacy figures look impressive!  But efficacy<\/em> and mite<\/em> reduction<\/em> are two different animals.  Efficacy compares the change in mite counts in the treated Test group, compared to that of the increase that took place in the Control group.  Since the mite infestation rate typically doubles each month, a treatment that merely held the mite count steady for 42 days would still calculate out to 64% efficacy.  Mite reduction just looks at before and after counts, and doesn\u2019t require a control group.  So although the spring treatment with 4 hung strips worked out to 68% efficacy, that meant that it really didn\u2019t decrease the infestation rate to any extent.<\/strong><\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Fig. 2  <\/strong> Their starting wash counts averaged only around 3-8 mites, so the figures above are only rough estimates.  Mite wash counts were reduced by all treatments (save for in spring, when the hung strips only held the count steady).  For the spring treatment, due to nibbling of the strips, they added 2 additional strips at Day 20 to the \u201cboosted\u201d hives (which, to no surprise, improved efficacy).  In autumn, beside the 4 hung-strip dose, they tested a range of doses and application methods.<\/p>\n\n\n\n

Takeaways: <\/strong>The efficacies that they obtained were impressive!  Note that they got same efficacy from laid-flat strips as they got from hung strips!  <\/em>And that efficacy was less at the dose of 3 hung strips, but didn\u2019t improve with 5 strips.<\/p>\n\n\n\n

<\/a><\/a>Their Conclusions<\/h3>\n\n\n\n

They observed no noticeable effect from VarroxSan treatment upon the adult or brood populations of the colonies, and concluded that: \u201c[VarroxSan\u2019s] efficacy depends on the time of the year it is applied, the dose, and the method of administration<\/em>.\u201d<\/p>\n\n\n\n

<\/a><\/a>My Analysis of their Results<\/h3>\n\n\n\n

VarroxSan appeared to be most efficacious at reducing the mite level when applied during autumn or winter.  Springtime application did not reduce mite levels, but did keep them from increasing (that efficacy was increased by applying a second half dose after 20 days).<\/p>\n\n\n\n

<\/a><\/a>WE DON\u2019T NEED NO STINKIN\u2019 SCIENTISTS!<\/h2>\n\n\n\n

But we beekeepers don\u2019t necessarily have to depend upon institutional scientists for field testing \u2013 the whole reason I started writing these articles was to encourage other beekeepers to do their own properly designed research and then share their results.<\/p>\n\n\n\n

<\/a><\/a>TIPS FOR RUNNING A FIELD TRIAL<\/h3>\n\n\n\n
    \n
  1. Define the specific<\/em><\/strong> research question you want to answer. Spend a lot of time on this step!<\/em><\/strong><\/li>\n\n\n\n
  2. Make up dummy charts of how you plan to present your results, and work backwards from there (this will show you what data to collect). Anticipate in advance any way that someone could criticize your methodology or analysis.<\/em><\/li>\n\n\n\n
  3. Run a comparative Control group along with your Test group(s).<\/li>\n\n\n\n
  4. Include a large enough number of colonies in a trial (the \u201cn\u201d) to allow statistical comparison between the results from each test group and the Controls. Due (due to ingrained colony-to-colony variability, this typically requires at least a dozen hives per treatmenttest group.).<\/li>\n\n\n\n
  5. Start with colonies of similar condition, in the same yard (or yards) in order to minimize variables, and assign the treatments randomly. Treat all the colonies exactly the same, other than the variable of the treatment(s) that you are testing.<\/li>\n\n\n\n
  6. Record every detail of the colonies and hives used, dates, weather, bloom, etc.<\/li>\n\n\n\n
  7. Take and record starting and ending (and perhaps midpoint) data (mite wash count, colony weight, colony strength) relevant to answering your question. If you\u2019ve run a Control group, I suggest using the Henderson-Tilton formula to calculate treatment efficacy [[6]<\/a>].  If relevant, download my calculator to compute efficacy [[7]<\/a>].<\/li>\n<\/ol>\n\n\n\n

    <\/a><\/a>TWO FIELD TRIALS FROM THE SOUTHEAST<\/h2>\n\n\n\n

    I\u2019m very happy that three beekeepers Greg Rogers, Scott Davis, and Bob Binnie independently ran field trials in 2025, and have allowed me to share their results [[8]<\/a>].  Let\u2019s start with the results of Greg\u2019s trial, run in North Carolina for 90 days (mid-May through mid-August) with 87 hives (in 8 different locations). (Figure x).two of their own 2025 field trials, performed in the Southeast [[9]<\/a>].  Both trials were intended to answer the question: \u201cWhich OAE treatment and application method, when applied to hives of the stock(s) that I\u2019m running, will result in the lowest increase in mite counts during the May through August treatment?<\/strong>\u201d They started their trials with colonies exhibiting mite counts in the 0-1 range, and measured them again after 3 months.  Uh-oh\u2026<\/p>\n\n\n\n

    Note:  \u201cThe label is the law\u201d.  <\/strong>VarroxSan\u2019s label specifies: \u201cTreat once the infestation reaches 1-2%\u201d (a wash count of 3-6 mites), indicating that VarroxSan is registered solely to reduce<\/em> an established infestation, not as a preventative treatment<\/em>.  But Bob, Greg (and I) feel that it is a best management practice to proactively keep your mite counts down to zero in the springtime.  Don\u2019t you hate how the EPA keeps putting us into the position of being scofflaws?<\/strong><\/p>\n\n\n\n

    Greg and Bob graphed out their results in Figures 3 and 4.<\/p>\n\n\n\n

    \"\"<\/figure>\n\n\n\n

    Fig. 3  <\/strong>Of interest is the difference between mite control by VarroxSan in Greg\u2019s yards and Scott\u2019s (I\u2019ve found that OAE treatment works best in yards with no mite immigration, but do not know whether that was a factor, nor whether there was a difference in bee stock or weather conditions).<\/p>\n\n\n\n

    Analysis:  <\/strong>There wasn\u2019t much difference in the results from the three treatments to the right.  Greg didn\u2019t run a control group, so we can\u2019t calculate efficacy, but we can estimate it (assuming that he started with mite counts of 1).  Since a mite population typically doubles each month, we would expect his mite wash counts to increase by a factor of about 8. So although the average counts in the the three treatments to the right went up to 4 (no reduction<\/em><\/strong>), that still suggests an efficacy<\/em><\/strong> of around 50%.  <\/strong>Greg Rogers ran his trial in North Carolina with 87 hives (in 8 different locations), for 90 days (mid-May through mid-August).  Although there was no Control group,  if we were to assume that his starting counts were 1, after 90 days of \u201cnormal\u201d rate of increase, we\u2019d expect them to double three times, to counts of 8.  So the three treatments to the right would calc out to about 50% efficacy.<\/p>\n\n\n\n

    Bob Binnie ran his trial with 811 hives in Georgia, using a variety of mite-resistant bee stocks (likely why his ending mite wash counts were lower than Greg\u2019s).  All hives started with wash counts of zero in May (see note), with final washes performed at the end of July and beginning of August.<\/p>\n\n\n\n

    Note:  The label is the law!  <\/strong>VarroxSan\u2019s label specifies: \u201cTreat once the infestation reaches 1-2%\u201d (a wash count of 3-6 mites), indicating that VarroxSan is registered solely to reduce<\/em><\/strong> an established infestation, not as a preventative treatment<\/em>.  But many of us would agree that keeping your mite counts close to zero in the spring is a Best Management Practice.  Once again, the EPA is behind the curve, and forcing us to be pesticide scofflaws.<\/p>\n\n\n\n

    \"\"<\/figure>\n\n\n\n

    Fig. 4\u00a0\u00a0<\/strong>Bob\u00a0did<\/em>\u00a0run a Control group, but both it and the other Test groups consisted largely of mite-resistant stock (an additional variable).\u00a0 This may be why there was so little difference in mite increase between his treated and untreated colonies.\u00a0 Since there are no error bars on this graph (to see the range of variation for each group), his collaborators will need to tease out is the effect of each queen stock (see [[10]<\/a>]) from the effect of each treatment. Bob Binnie ran his trial with 811 hives in Georgia, using a variety of mite-resistant bee stocks (likely why his ending mite wash counts were lower than Greg\u2019s).\u00a0 All hives started with wash counts of zero in May, with final washes performed at the end of July and beginning of August.\u00a0 My seat-of-the-pants estimate (since you can\u2019t perform an efficacy calculation starting from zero) is that efficacies of Bob\u2019s treatments were in the same ballpark as Greg\u2019s, but with the complication that mite-resistant stock was involved.\u00a0 The one standout is the great performance of the Swedish sponges!<\/p>\n\n\n\n

    Analysis: <\/strong>Of interest is that there was again little difference between Varroxsan hung or laid flat<\/em>.  And that the best performers appeared to be the Swedish sponges (he used a 55% oxalic x 45% glycerin formulation) and the Canadian strips.<\/p>\n\n\n\n

    Bob and Greg both ran great trials (with large \u201cn\u2019s\u201d), to answer the question: \u201cWhich treatment and application method, when applied to hives of the stock(s) that I\u2019m running, will result in the least mite increase between May and August?\u201d<\/strong> So Bob started with mite counts of zero, and followed up with ending wash counts, to measure the degree of increase (from the graph, we\u2019re unable to see in how many hives the mite count didn\u2019t increase at all).\u201d, which should allow his collaborators to tease out whether there were statistical differences between the groups (there are no error bars on their graphs, so we can\u2019t yet tell).<\/p>\n\n\n\n

    Neither of these trials were designed to see whether the treatments could reduce<\/em><\/strong> a mite infestation (you can\u2019t measure reduction<\/em><\/strong> when starting with a count of zero).  But I\u2019m surprised that the average<\/em><\/strong> counts of the treated colonies all went up as much as they did, suggesting that OAE may not work as well in the Southeast as it does in California (this may have to do with humidity).<\/p>\n\n\n\n

    Neither of these trials were designed to see whether the treatments could reduce<\/em><\/strong> a mite infestation (since you can\u2019t reduce from a starting mite count of zero), nor to necessarily calculate efficacy (Greg\u2019s trial lacked a Control group).  Nor were their trials designed to easily tease out the effect of some colonies being innately mite-resistant (Bob\u2019s Control group consisted largely of GWB semi-resistant stock).  I am in no way criticizing either trial, since they appear to have answered their question nicely, and fulfilled their practical application.<\/p>\n\n\n\n

    The takeaways from these two trials (and their discussions on video) were:<\/p>\n\n\n\n