Formic Pro vs Bayverol

Testing miticides alongside each other

by: Dr Madlen Kratz
NSW DPI Honey Bee Industry Development Officer

There is still a lot to learn about how often we may have to treat colonies with miticides and their effectiveness under various environmental conditions throughout the year and region to region. This can be a tough and costly decision for larger beekeeping operations.

For the purpose of this article, I would like to share an experience of using a synthetic versus a non-synthetic miticide treatment on 50 colonies at the same apiary.

This trial was conducted at Tocal Agricultural College with help from our current NSW Varroa Development Officers Slavi Nenov and Emily Noordyke.

Mite free research apiary

Prior to the trial the 50 colonies were located 2hrs north of Tocal near Old Bar (NSW). The hives were brought to Old Bar from a mite free location in January 2023. The first-time mites were detected in the hives was at the end of October 2024. At the time 14% of the hives were infested with 1 mite in an alcohol wash. The remaining 86% of hives showed no detectable mites in an alcohol wash. What surprised me to some extent was how much variation there was in mite numbers between hives over the next couple of months even though all hives were balanced for strength and getting infested at the same location for the first time. Mite counts in alcohol washes ranged from 4 to 14 ~ 2.5 months later (mid- January 2025). By this time the colonies were ready for their first mite treatment (9+ mites as the recommended treatment threshold over the summer months). Noting, that best practice is to treat all hives in an apiary, even if a small percentage of hives is still below recommended treatment threshold. The reason being that hives at the same apiary can re-infest each other with mites through for example drifting or robbing.

The 1st mite treatment – Bayvarol vs Formic Pro

We brought the colonies back to Tocal for research reasons, which delayed the treatment until mid-February, but to our ‘delight’ provided a perfect opportunity with a window of cooler temperatures to compare two miticide treatments alongside each other. We treated 26 hives with Bayvarol (a synthetic miticide: Flumethrin) and 24 hives with Formic Pro (a non-synthestic miticide: Formic acid). At this point the hives had between 3 – 36 mites in an alcohol wash of 300 bees (mid – February).

Bayvarol and Formic Pro miticides work in very different ways as summarised in Table 1.

Table 1. Some comparisons of Bayvarol and Formic Pro as a miticide. Adapted from varroa.org.au

Active Ingredient and formulation	Flumethrin (synthetic pyrethroid) in impregnated strip	Formic acid (organic acid). Formic acid formulated in a saccharide gel strip.
Treatment Period	6-8 weeks	7 days
Effectiveness	95.99% (where mites are not resistant)	61-98%. Highly variable due to temperature.
Targets	Phoretic mites on adult bees	Phoretic mites on adult bees and mites in brood (up to 60%)
Resistance Risk	Yes, if used off label or sequentially with other products with the same MOA (e.g. Apistan™).	No.
Mode of Action (MOA)	Contact. Targets Varroa nervous system causing fatal failure and muscle spasms. Same MOA as Apistan ™. Rotate with products with different MOA.	Fumigation. Inhibits cellular respiration causing respiratory acidosis.
Conditions for Use and Withholding Period (WHP)	4 Bayvarol™ strips per brood box in a full colony for 6-8 weeks OR 2 strip for 6-8 weeks in a nucleus colony. CAN BE used when supers are present (Schedule 5 Poison).	2 strips above brood box in a full colony for 7 days. Colony must have full open entrance and closed bottom board if ventilated. Environmental temperature must be between 10-29.5°C. May cause colony agitation. DO NOT use in nucleus colonies. Only full size colonies with 6 or more frames fully covered by bees can be treated.
Contamination Risks	Hive products, including wax. DO NOT SELL COMB HONEY, DO NOT MAKE BEESWAX. Honey extracted from the brood box must be tested for maximum residue levels (MRLs).	Hive products, including wax. May taint honey.
Residues	Accumulates in brood combs with repeated application. Residues in propolis.	Honey taste, observe withholding period as per product label.

This is one of the challenges in comparing miticides with different modes of action, treatment times and so on. However, this trial allowed us to see how effective a particular miticide is to another at one point in time! I would like to emphasize that because especially the non-synthetic treatments are much more dependent on environmental factors, so it wouldn’t be fair to judge its effectiveness as a whole against one point in time.

For that reason, I would like to encourage all beekeepers to take detailed notes when applying miticide treatments such as:

Hive status (strength, disease status, amount of brood, queen age)
Hive configuration (number of supers, entrance width, type of bottom board)
Environmental conditions (temperature, humidity, floral resources)
Effectiveness (testing mite loads before and after treatment)
Cost of treatment

The above records will help you gain a better understanding about what treatments may be more suitable under what conditions and time of year across your beekeeping environments.

This was the second time I have used Formic Pro as a treatment on hives within the last 18 months. The first time was on 7 hives located at Tocal in June 2024. As you can see in Table 2, the effectiveness of formic acid varied across time periods and environmental conditions. In June 2024 the mite treatment was more effective than in February 2025. The environmental conditions were also much better in June 2024 (spotted gum flowering) compared to February 2025 (grey box flowering). Luckily, the bees came back to grey box with some good tea tree pollen stores from the coast. The bees in June 2024 were of similar colony strength but with less brood at that time of the year (~15 frames of bees, 4 frames of brood including 0.5 frames of drone brood) than bees in February 2025 (~14.5 frames of bees, 6.4 frames of brood including 0.5 frames of drone brood).

In both instances there was a large variation in treatment effectiveness between hives ranging from 17 – 88% in June 2024 and 4 - 67% in February 2025.

Table 2. Treatment outcome of Formic Pro over two points in time.

In both instances there was a large variation in treatment effectiveness between hives ranging from 17 – 88% in June 2024 and 4 - 67% in February 2025.

Temperatures

Formic Pro can only be applied with an outside temperature range of 10-29.5 °C. The first 3 days of treatment with Formic Pro are the most critical that temperatures stay between 10-29.5 °C.

In June 2024 the temperatures ranged between min: 5.7 – 12.8 °C and max: 17.2- 19.9 °C during the day. In February the temperatures ranged between min: 10.8 – 22.5 °C and max: 24.2 and 36.8 °C. Noting that the 36.8 °C was on the last day before the formic treatment was being removed.

Lost queens

We assessed all colonies for their queen presence (all marked and clipped) before and after applying Formic Pro and Bayvarol treatments (Figure 1). No queens were lost during either treatment. In the case of Formic Pro treated hives, this was the case for both June 2024 and February 2025. However, the queens stopped laying for a few days after applying formic Pro treatments, which we could tell by the age of the brood. Queens were laying well again after the initial few days.

Queen age

Jun 2024: 18 months

Feb 2025: 6 – 14 months

Dead bees

Beekeepers have previously reported piles of dead bees at the entrance of hives post formic acid treatments. We did not observe any more dead bees than you would normally see at the hive entrance. The bees however immediately responded to the formic acid once placed inside the hive, by increasing their fanning behaviour and bees were seen bearding at the front of the hive (Figure 2, 3).

Figure 2. Bees bearding at the hive entrance. Note: These hives have ventilated bottom board pollen traps, which were blocked off with a vinyl mat during treatment.

All hives treated with Bayvarol showed up with zero mites in an alcohol wash 8 weeks later (max. treatment period).

A note on re-queening

Beekeepers have been asking about the re-queening success during or after treatment. From overseas experience, synthetic treatments are much safer when it comes to re-queening success during treatment. In either case, it’s better to avoid re-queening (when possible) while treating hives for mites.

During the trial in February 2025 we re-queened some Formic Pro treated hives straight after the pads were removed with 100% success in poor weather conditions (overcast and drizzly). At the same time some of the Bayvarol hives were requeened (3 weeks into the treatment) with all queens being accepted.

Figure 3. Formic Pro pads applied above the brood nest.

The caveat with synthetics vs non-synthetics

Synthetic chemicals are ‘easy’ to use. Well at least for now, they are highly effective against mites and once applied, you ‘just’ need to keep an eye on your calendar for when they need to be taken out again. They also provide an extended treatment period of a minimum of two brood cycles (6 weeks). Over time however, they are the first chemicals that mites can build up resistance to for various reasons and their effectiveness diminishes. This can be seen around the world with, for example, Bayvarol simply not being effective anymore due to having become a heavily used treatment option in various countries. Back-to-back use of a miticide with the same mode of action (they kill the mites the same way) is one major route of resistance.

Non-synthetic treatments such as formic acid and oxalic acid are much more difficult to use. Well, they are much more variable and dependent on climatic conditions, hive strength and mite loads. In most cases non-synthetic treatments are simply not effective enough in reducing mite numbers below threshold once mite numbers in colonies are too high or in areas of high reinfestation. At the same time the way these acids work against mites makes it very hard for mites to build up any resistance.

During times of heavy reinfestation some beekeepers may not have any other options than to rely on synthetic treatments. This hopefully will change once mite numbers plateau out in the environment. For more information on the miticides used in this trial use the QR codes below:

Bayvarol resources including permit, safety data sheet, product information and usage video can be found at Varroa.org.au

Formic Pro resources including permit, safety data sheet, product information and usage video can be found at Varroa.org.au