Varroa is the number 1 enemy. This mite is the major cause of nearly all the problems that affect the western honey bee. Where ever it is found.
Varroasis is not a disease but an infestation by the parasitic mite Varroa destructor (previously jacobsoni). Since reaching this country in 1992, it has become endemic throughout the U.K. and most of the world. Your colonies will almost certainly have varroa mites.
Doing nothing is not an option – without treatment colonies will die within 3 years. You must learn to monitor colonies for levels of infestation and treat when necessary. As with the errant farmer and his chemicals the “leave it in a bit longer” beekeeper has produced mites that are resistant to the approved varroacides. Their failure to keep to the time-scale has resulted in resistant mites.
Research continues to find new varroacides and until they arrive we are left with other methods. The different methods are grouped together under the heading of “Integrated Pest Management”.
Fit varroa screen floors to hives in order to monitor levels of infestation.
Uncap drone brood.
Place a super frame in the middle of the brood box and destroy the drone brood built under the frame (varroa mites prefer drone brood). You must remove the drone brood traps before the drones emerge - leaving them will have the opposite effect! 1,000 mites are now taken to be the highest acceptable population.
Dusting with icing sugar works by covering the bees and frames with fine granules which prevent the varroa mite for getting a grip and so they fall off and through the mesh floor never to return.
The use of hive cleansers is a subject of much debate and argument within the legislative and regulatory arms of government. Some departments would like to see ALL preparations however natural and innocent being registered as vetinary medicines. This would result in beekeepers trotting off to the vet every time they wanted to use a drop of tea tree oil in a spray bottle in preference to using smoke for example.
The current situation is that the use of hive cleansers is tolerated but the hawks are watching our every move and will no doubt pounce when they find more than a trace of our hive cleanser in some honey they have tested.
There are two main hive cleansers available to us.
Firstly Thymol. This is a concentration of Thyme oil. It is available commercially as Apiguard and comes as a paste in small metal trays. These are placed over the brood nest in autumn after the honey has been removed. The heat from the nest evaporates the Thymol and the fumes suffocate the mites on the frames but do no harm to the bees. The treatment is done twice at 2 weekly intervals so as to catch two hatchings of mites.
Thymol is also available in crystal form from beekeeping suppliers. It is used as an additive to sugar syrup to stop moulds forming but when used in a suitable frame they can also be effective against varroa in exactly the same way as Apiguard but at a fraction of the cost.
Our second weapon of choice is Oxalic Acid.
Oxalic Acid has been used in Europe for the treatment of varroa for over 30 years without incident.
It is an organic acid found naturally in crops such as Rhubarb.
The preferred method of use is to apply a 3.2% (by volume) solution in sugar syrup. The syrup is trickled onto the frames and the bees at a rate of 5ml per “bead” of bees.
In the same way as Thymol works the oxalic acid vaporises in the heat of the hive and suffocates the varroa by burning their breathing tubes. There is no effect on the bees.
For those who cannot wait or have a lot of hives there is an oxalic acid vaporiser which is operated from a car battery and consists of a small heating plate to which a few grams of oxalic acid crystals are added. The heat plate is pushed along the floor of the hive under the brood nest and heat is applied. The crystals evaporate within a minute and coat the frames with acid. The result is the same. Efficacy in both cases is over 90%.
There is no 100% knockdown treatment. Varroa breeds in sealed cells of brood – since a newly hived swarm has no brood, it can be treated to give a clean start.
Apart from seeing mites, you may see stunted bees with distorted wings resulting from the varroa mite sucking the larval ‘blood’ – this is usually an indication of a high level of infestation.
The puncturing of the larvae enables non-apparent viruses to take hold such as Slow Paralysis Virus and Deformed Wing Virus (Acute, Chronic, Cloudy Wing Viruses) – the colony dies from virus infection.
Although varroa is now endemic in the UK and is no longer a statutory notifiable disease, the NBU will continue to offer advice on its control as it does for other serious non statutory diseases. http://beebase.csl.gov.uk/
As a “ready reckoner” the table below gives an early warning to varroa mite density in your hive. To use the table you need a clean white board to put under your mesh varroa floor for 24 hours. The light colour of the board helps you to pick out the mites from the other hive debris.
Average Daily Natural Mite Mortality
Jan - March <2 no action 2-7 plan future control 7> consider control
April - June <1 no action 1-7 light control 7> severe risk
July - Aug <2 no action 2-8 light control 8> severe risk
Sept - Dec <6 no action 6-8 light control 8> severe risk
Light control might be drone brood culling, artificial swarming, dusting with icing sugar, etc. rather than heavy control using chemicals.