1. Background and Reasons for Winter Bee Mite Treatment
Fall mite treatments aim to protect young winter bees from mite-related issues that arise from drifting and robbing at the season’s end. While there is still brood in the hive, the goal is to keep mite numbers low enough to reduce harm to the colony.
As winter approaches, honeybees come to a phase: the natural brood pauses. Honey bees in most regions temporarily stop raising broods.
Varroa mites need bee brood to reproduce, and they remain shielded from most treatments while developing under brood caps. In the early winter bee colonies become broodless, exposing the mites vulnerable.
As we have learned about varroa mite biology Varroa mites cease reproduction and remain at the phoretic mite stage. They feed on bodily fluids from the bees and overwinter with them. They lower the protein levels in winter bees, essential for their immune defenses and spring growth.
2. Winter is the Best Time for Oxalic Acid Bee Treatment
We can take advantage of this natural brood pause to treat mites. Oxalic acid embodies an organic acid treatment approach, like formic acid.
Oxalic acid is far less corrosive than formic acid. This is because formic acid has more hydrogen ions when it dissolves in water. This higher concentration means formic acid is more corrosive. Beekeepers feel safer applying oxalic acid.
We apply it during the honey flow season by keeping honey supers in the hives. It also eliminates winter mites.
Oxalic acid bee treatments best control Varroa mites in midwinter when bee colonies are broodless. This is because oxalic acid only kills phoretic mites on adult bees, not those in capped cells.
3. Mechanism of Oxalic Acid Treatment
The exact way oxalic acid kills mites is not completely clear. However, the main scientific idea is that it enters the mite through its feet and poisons its bloodstream.
Expert Gerhard Brüning experimented by vaporizing oxalic acid in a hive. He found that the acid collects on the sticky parts of the mite's legs, called the paired lobes (pulvilli), and forms a crystal. After three hours, the mite dies. The crystal then breaks down, leaving only a tiny drop as residue.
The idea is that the sticky lobes must be wet for the mite to attach to a bee or another surface. Moisture enters through the mite's leg and hemolymph. Oxalic acid reaches the mite's hemolymph through the lobes and kills it.
4. How to Tell if Your Colony is Broodless
Monitor the brood nest temperature
Bee colonies with brood keep their brood nest at a higher, stable temperature (32-35°C) than colonies without brood. We can tell if a colony has the brood by checking the temperature. Broodless colonies have a lower core temperature, usually around 18°C.
Observe the Varroa tray
Look for new biscuit-colored wax capping crumbs, which indicate that brood is emerging. However, it's possible to see the first brood emerging while there's still more capped on other frames. Make repeated observations over 10–12 days to get a better idea.
5. Application Methods of Oxalic Acid
Vaporization
Oxalic acid vaporization (OAV) treats honey bee colonies infested with the Varroa destructor mite. Also called oxalic acid sublimation, this method uses a tool like the Varrox vaporizer. It heats and vaporizes oxalic acid crystals. Some say that vaporization leads to higher mite drops than the trickle method.
Oxalic Acid Slow-Release Strips
Another method is to use oxalic acid slow-release strips. By slowly releasing oxalic acid on a mat or hanging strip, the mite count drops quickly at first. Then, it gradually decreases over the next two months.
We recommend using MELOXAL Strips. These are high-concentration oxalic acid slow-release strips. They are composite fiber strips with the active ingredient OA. With high levels of content, a single placement lasts up to 6 weeks.
The treatment's long-lasting effect means beekeepers do not need to open the hive to replace the strips. This reduces frequent disturbances to the bees in cold weather and helps support their winter survival.
Trickle
The most popular method in Europe and Canada involves mixing oxalic acid with a sugar and water solution. This solution has a 1:1 ratio of sugar to water. Then, use a syringe to drip the mixture between the hive frames and onto the bees. Beekeepers widely use this method during a brood-less period, such as late fall or winter.
Consistent Varroa mite management is key to successful beekeeping. Consider making oxalic acid treatment a regular part of your winter care plan.
