8 Weeks After Flumethrin Treatment

Assessing Hive Health after Summer Miticide Application

Several months back I wrote about flumethrin as a Varroa mite treatment. Here I report the results of an eight week of this Bayvarol treatment on three colonies, applied during the summer of 2023-2024. Yes, the supers were removed, no, I did not harvest (much) honey this season.

This post is a review of my experience with flumethrin. In summary:

• Mites were detected in one of the hives following a laboratory analysis of the sticky boards.
• 4x flumethrin strips were applied inside each brood box for eight weeks in late December.
  • One hive swarmed 3 weeks later. Swarm was captured, re-homed, then robbed and died – retold in robbing bees.
• Hives left untouched until inspection in late February.
  • Testing for Varroa (alcohol wash) produced negative results in all three hives.
  • Two hives showed high number of honey-locking in brood frames.
    • One hive had 3x fully capped frames.
  • Colonies in good health, Queen continues to lay eggs.
• Strips removed and hive were closed for three days to clear the remaining flumethrin vapours.
• Honey super returned end of February.

Should I Leave the Queen Excluder on When Using Flumethrin?

Leaving the queen excluder on does not impact the treatment, and after trailing both methods, I suggest applying flumethrin strips without the excluder.

After removing (and safely storing) the honey supers, the first next obstacle was what to do with the excluder. Leave it on? Take it off? It doesn’t impact flumethrin treatment, so you’re free to choose whatever is easiest. I had three hives, so I tested both methods.

The gaps between the excluder’s bars assisted in strip placement, however they obscured the gaps between frames. This was overcome with a bit force, at the cost of damaging comb. Nothing the workers couldn’t handle.

Placing the strips without the excluder was much easier. When doing so, I saw where each gap between frames was, and utilised the two hooks at the end of the strips to place the treatment between the frames’ top bars. A few days later, the strips would be locked in place by beeswax, and the hives were (theoretically) left alone for eight weeks .

Oh Dear, My Hives Swarmed While Under Flumethrin Treatment

Three weeks in, the middle hive swarmed. This was 2nd January 2024, and approaching the tail end of the swarming season. I had done the necessary swarm checks prior to placing the flumethrin strips. I would guess that they swarmed as a result of rapid increase in colony density after removal of the honey supers.

This is an oversimplification, for swarming is multifactorial: The queen’s genetics surely played a part, as she had higher swarming tendencies than the two other queens. All up, it was bad luck on my part. That swarm was captured and placed into the apiary, and I phoned the state department to request additional flumethrin strips (they were freely provided at the time).

The official advice was to “monitor the hives and perform a mite check once they settle in, then we’ll determine next steps”. I knew the swarm was from one of my own, so I had no issue with immediately placing it in the apiary. I didn’t have to worry about an alcohol test or Varroa testing with this swarm, they got robbed by the other hives and ended up absconding.

Why are Honey Supers Removed During Flumethrin Treatment?

Short answer: The flumethrin fumes can be absorbed by the beeswax, and overtime that can transfer the chemical into the honey itself. Honey that meets the regional minimal residual limits is still fit for sale/human consumption, however I erred on caution and removed the supers.

A longer answer: Flumethrin is fat soluble (lipophilic), and stable at room temperature, maintaining a steady release of the chemical while within hives. The lipophilic nature enables it to adhere onto the waxy exoskeleton of bees as well as the wax comb. In most cases, the flumethrin contamination of honey are due to the reuse of old wax comb.

Flumethrin is more likely to dissolve in wax than other miticides, and accumulates into higher concentrations over time (Yu et al., 2015). When bees store honey in flumethrin-containing comb, some of the residues would have transferred into the honey itself by the time of extraction. Once again, contamination is more likely when flumethrin is used during nectar flows as bees are actively ripening nectar and placing it inside comb.

How do I Know if the Flumethrin Treatment is Successful?

Perform a mite check. I performed an alcohol wash on each hive and did not detect any pests, indicating a successful Varroa treatment. Of course, the local authorities could perform a sticky board check again, and the lab results would confirm that mites are detected… As a great bear once said, you can never tell with bees.

In severe infestations, perhaps the goal is a reduction rather than eradication of mites, keeping their numbers down to manageable levels. In most cases honey bees cannot overcome mites alone, so a follow-up treatment would be warranted to prevent an increase in Varroa populations.

What if Mites are Still Detected?

That’s a real possibility that arises from improper treatment application or miticide-resistant Varroa. In such situations, monitor the populations – perhaps they’re low enough that the bees can get by for another season or two before needing beekeeper intervention. Honey bees would be physiologically stressed following flumethrin treatment (see below), and it’s best to give the hives a break.

Look into non-chemical methods for Varroa management. If the colony is actively producing drones, consider drone brood trapping, in which the drone comb is removed and frozen after the majority of the frame is capped. This method is more labour intensive, but less impactful on the bees, and can be used while the bees recover from miticide application.

If mites are still detected in the colder months, then it’s best to let the hives bee and monitor, take action in warmer conditions. You don’t have to agree with me, and are welcome to try your own way.

What to do After Flumethrin Treatment

After flumethrin treatment, give your bees a break for a few days, or a week. No extensive inspections, no overloading with two full empty supers. Qi and colleagues showed that flumethrin activates the immune system of bees, disrupting normal function (Qi et al., 2020). This effect was most pronounced in newly-emerged bees. Considering that the average bee worker lives for 42 days, an eight-week treatment period would mean the entire colony populations have been affected by flumethrin.

So after treatment, the colony is more vulnerable, whether to other diseases or pesticide poisoning. Is a flumethrin-treated colony also more likely to be re-infested with Varroa? Maybe and it’s why routine inspections are required.

Hive Inspection Post Flumethrin Treatment

A few days after treatment, I conducted a full brood inspection. Unsurprisngly, most frames were honey-locked – the queen did not have much room to lay eggs. Frames with fully-capped comb were discarded and replaced with fresh frames. I know, I know – I could have extracted the liquid honey; I chose not to.

All three queens were laying eggs, and larvae/capped brood were present. Since around 70% of comb was honeylocked, the hive population will decrease in the coming weeks as the worker population is replaced at a lower rate. I also placed a single super onto each hive – it is autumn at the time of writing and our winters are mild – one full-depth super will keep the bees busy until next spring.

In Hindsight: Flumethrin Alternatives

I was part of the initial government program for Varroa treatments. From September 2023 until end of January 2024, beekeepers who had confirmed Varroa infestations received a packet of flumethrin strips to manage the initial mite loads until commercial supplies were readily available.

Now that additional chemicals were approved (Formic acid, oxalic acid, fluvalinate, amitraz & thymol), I would have used formic acid, as my treatments were applied in summer for peak populations, and formic acid can be applied with the supers on. I also could have waited and monitored mite levels throughout the summer until Formic Pro was made available. Alas, hindsight is 20/20.

As it stands, I plan to treat my hive depending on the season, and the Varroa populations, as shown below.

You’re welcome to make your own methods, or comment on mine – there are many ways to manage this pest.

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