Formic Pro is an excellent product for rapidly knocking down a heavy mite load in a hive. It has some great advantages: It kills mites under the capped brood, where most of the mites reside. It can be used while honey supers are in place, with no detriment to the honey, and it is quick. But because Formic Pro is such a powerful varroa miticide, we have always approached it with some caution in our own apiaries. In our experience there is not much room for error in application. We have seen how easily our customers can get into trouble with formic acid, and this should not be surprising as it requires the beekeeper to use their skill in balancing several interacting variables: temperature and weather, colony size, hive size, ventilation, and dosage. (Actually, all mite treatments need this balance, but formic acid particularly so because of its strength.) Below we cover some of the more common traps we see our customers encountering when using this product:
Pause in Egg Laying: A common side effect of formic acid treatment is a cessation in queen laying during and for a few days after treatment. In our experience, this is often misinterpreted as a dead queen (and occasionally it actually is). This often leads to anxious beekeepers panicking and trying to fix a non-problem, making things worse.
Two weeks ago, a customer reported a classic example of the same pattern. He had treated his hive with formic acid, which resulted in a complete absence of brood and apparently no queen. Seven days later, he came to buy a double screen so he could combine the remnants of the colony with a strong hive for winter. But when he went to transfer the colony, he discovered the queen was laying a beautiful pattern and all was right with the word. I have seen this pattern of a pause in egg laying so often that I try to warn customers to wait before requeening. So, if brood production ceases during or shortly after you have done a formic acid treatment, don't rush to the conclusion that the formic acid killed the queen. Wait a few days and inspect again before buying a new queen.
Ventilation and Temperature: Another common issue when treating with formic acid is ventilation. We were recently reminded of this by a couple of unfortunate local customers:
The first customer wanted to knock the mite-count down quickly in three of her hives to ensure strong winter brood development. Formic Pro is an excellent choice for this situation. She applied the full two-pad dose between two the brood boxes of her three hives and kept her already-installed robbing screens in place. She did not ventilate the hives and did not have a honey super on top. The temperature was in the high 70 degrees F. On inspecting the hives after the first 24 hours of treatment, she found a huge bee kill, much of it trapped behind the robbing screen. Not surprisingly, the queen did not survive. The second hive also had a sizeable bee kill but not as high as the first and it is now brooding up well. The third hive had the smallest bee kill, and now has a tight but smaller brood pattern.
Naturally, she was upset at the bee kill and the lost queen. This result was probably avoidable, and we feel bad for not cautioning her adequately about the necessary precautions: unobstructed entrances, use of a super as a refuge for the bees, and preferably some ventilation at the top.
The second customer had a great year before doing her formic treatment. She had three thriving hives from which she had harvested a bumper honey crop. She used the full-dose treatment regime (two pads together between brood boxes), and she had honey supers for dead air space on each hive above the brood chamber but no top ventilation. She did not have entrance reducers or robbing screens installed.
Eleven days into the treatment, she found two of her colonies (the strongest two, of course) had absconded. We certainly don't know for sure that the formic acid triggered the absconding, but another customer recently reported a similar story. We suspect that these losses might have been avoided if she had used the half-dose treatment method described by the manufacturer.
Our Precautions: So, what precautions do we take with this product in our own hives? Some of our precautions might seem excessive, and they are not all in the product usage instructions, so we cannot call them recommendations. They are simply the precautions we take.
1. We know plenty of beekeepers that use formic acid routinely, but we save it for when there is a serious mite problem that needs a fast-acting and strong miticide. Additionally, we use it when the weather is below 80F, whereas the instructions allow up to 85F.
2. We make sure to have a honey super on top of the brood chamber as a refuge space for the bees.
3. We also have a Vivaldi Board (ventilation board) in place for supplementary ventilation. This likely reduces efficacy a little, but we consider the loss a good trade-off.
4. We make sure the entrance is unobstructed. This means no entrance reducers or robbing screens during the treatment, so the bees are free to beard as they need.
5. We use the half-dose treatment regime described by the manufacturer, where, rather than applying both strips at once, we apply one for 10 days followed by a second if it is needed. (We check our mite trays before applying the second strip.)
6. We don't remove the mite tray from the screened bottom boards, as we don't feel this actually changes upward air flow via the Vivaldi Boards significantly when the entrance is unobstructed (no entrance reducer or robbing screen installed).
7. In some cases, the mite pads prevent proper closure between brood boxes. In the late summer/early autumn, this could expose the hive to robbing. This can usually be fixed by scraping off the burr comb that is between the frames of the two brood boxes.
We freely admit to being overly cautious with formic acid in our own practice. But what is your experience with formic acid? Do you use it routinely or only occasionally? How successful was the treatment? Tell us what you do to avoid problems.
(For transparency, we should note that we are resellers of Formic Pro, and we have the highest regard for the manufacturer, NOD Apiaries.)