The last apiary session of 2018 was led by Stephen and Glynis on Sunday 16th December, a cold, but luckily dry day. We were to learn about how to safely use oxalic acid - a powerful varroacide which is corrosive and toxic to both man and bee if used incorrectly.
This is the ideal time of year and ideal week since the key elements are a broodless colony, a tight ball of bees and before the winter solstice sometime after which the queen renews laying.
Don't open up hives if the temperature is below 3 C. If sealed brood is present it must be removed since the treatment cannot penetrate through the wax cappings. If no brood is present then all the remaining mites in the colony are phoretic (on the bees) so vulnerable to oxalic acid. This needs to be done quickly to stop the bees getting chilled. Smoke under the crown board and carefully examine those frames with bees on.
DO NOT SHAKE THE BEES OFF. Instead use the back of your fingers/hand to very gently move them aside so that all cells can be seen. Move through the box and close up the frames allowing the bees to settle. Ideally this inspection should be done 1 or 2 days prior to treatment but at this apiary session we needed to carry on with the treatment phase immediately.
Of the 6 hives in the apiary two contained sealed brood which was removed. The varroa can sometimes be seen in the ‘mush’ of brood extracted, but be careful not to confuse red eyes of the pupae with adult mites!
The sight of varroa mites feeding on pupae goes some way to ameliorate the sinking feeling of destroying brood. This is an appropriate time to also check stores.
Both trickle and vaporisation methods of application were demonstrated, but first there was a safety briefing!
Oxalic Acid is a licensed veterinary medicine sold under the brand name Api-Bioxal. It comes as a 175 g and 35 g sachets containing a fine white powder (oxalic acid dihydrate with glucose and silica included as excipients. Api-Bioxal is the only oxalic acid product licensed in the UK for sublimation; 175 g of Api-Bioxal (£48) is enough to treat 50 hives; 35 g (£12) sufficient for 10 hives).
Due to the corrosive nature of oxalic acid, whether as the powder, liquid or in vaporised form, safety precautions are necessary throughout when handling this substance. That means having a FFP3 mask, goggles, rubber gloves and plenty of clean water nearby to wash off acid in the event of a spill. An eyewash bottle should be available. Any containers containing oxalic acid must be clearly labelled and date of preparation of solutions written on the container.
When ingested oxalic acid can be toxic (one tea spoon /20-40 g can cause irreversible kidney damage. It is highly corrosive on skin, eyes, nose and lungs.
Solutions should be made up in a draught-free area to prevent dust blowing around. Surfaces and all utensils should be washed down with plenty of water after preparation. Protective clothing should be washed after use. Keep pets and members of the household out of the way.
Manufacturer's instructions should be followed. Basically the process involves making up 50% sugar syrup and then adding the oxalic acid powder: 35g dissolved in 500 ml of syrup makes 4.2% w/v solution. Accurate weigh out the sugar, water and oxalic acid powder because under-strength solutions will give a poor mite kill and over-strength (5%+) may kill the bees. LABEL CONTAINERS OF OXALIC ACID SOLUTION and KEEP OUT OF REACH OF CHILDREN
The solution has a short shelf life of a few weeks if refrigerated. Alternatively, a product called Oxybee is available which can be stored in the fridge for up to a year after the solution is made up.
The "trickle" method is quick, simple and good for those with just a few hives. It involves trickling 5 ml of the 4.2% oxalic solution along each seem of bees in the hive. Those on brood and half or double brood may need a torch to see the seems of bees.
Use either a syringe or fixed unit bottle to trickle 5 ml of mixture along each seam in the brood box. Use a finger/marker to keep track of each seam as you move through the box.
Do not vaporise oxalic acid if members of the public or livestock are nearby.
The “vapour” or sublimation method is less toxic to bees more effective according to research at LASI, with mite kill rates approaching 100%. Care must be taken to ensure the hive is well sealed by using a solid floor or sheet of wood placed under the open mesh floor and the entrance and rear gap should be sealed with wood, tape or wet sponge, jay cloths etc. According to a 'trusted source' at least two people this year have been hospitalised from the effects of oxalic acid vapour inhalation.
The Api-Bioxal powder contains glucose which causes the vaporiser pan to be coated in a film of burned sugar when heated. To avoid having to clean this out after every vaporisation, cover the pan with metal foil.
All gaps in the hive must be blocked to avoid vapour loss. The rear of the hive can be blocked with a piece of wood with a notch to accommodate the handle to the vaporiser. Once inserted, the charged vaporiser is heated to 250-300 degrees Celsius, which sublimates the oxalic acid into the hive. The vaporiser is powered by a battery, and as with all battery powered kit check the battery is charged and that the connections are correct. Handle lead acid batteries with care.The vaporisation of the oxalic acid powder within the hive should be timed as per the product instructions.
The battery is disconnected after 3 minutes and the hive is left sealed to allow the vapour to continue to diffuse through the hive for ten minutes.
It's a legal requirement to complete a veterinary medicines record card or your hive records with the batch number, expiry date and dose of any medications given to bees.
After either process has been undertaken it is useful to know what your mite drop is over the next week by fitting a varroa board under the hive. The mite drop would be expected to be high after the first day, then even higher as the oxalic acid treatment continues to take effect and then to reduce to almost nothing over the following week. Results will be posted on this blog next week.