Varroa is a mite that lives on bees and unless it is controlled can eventually cause the colony to collapse. Varroa are extremely widespread and it's likely that you will come across them too. The good news is that there are lots of ways of treating varroa and by being vigilant and spotting an infestation early you can reduce the number of mites to a level that isn't harmful to the colony.
How To Spot A Varroa Mite
You might think that the varroa mite would be difficult to spot but if you know what you are looking for they stand out quite clearly. The picture on the right shows an adult female varroa mite.
How Do The Mites Live?
Varroa mites live off the bee themselves. They reproduce inside the sealed cells of the brood. Just before the cell is sealed the female mite nips inside and sits under the larvae. Once the cell has been sealed over the mite establishes a feeding site on the immature bee. She will then lays about 5-6 eggs. The female mite lays just one male egg and this mite mates with the females when they hatch. The male dies when the cell is opened and any female mites not yet mated with are therefore sterile. The mites like to favour laying eggs inside drone cells because these take longer to hatch than the worker bees.
During the summer the mites live for about 2-3 months. They survive over winter by living on the adult bees but aren't able to reproduce because the bees aren't raising any brood. The mites won't start increasing their numbers again until the spring when the queen starts laying again.
What Effect Do Mites Have On Bees?
The bees that are in the cell with the varroa mites usually survive but are not able to grow properly. They may be smaller, have deformed wings or simply not live as long as healthy bees.
How To Treat Varroa
Varroa is a common problem for bees to suffer and there are often new treatments available to try. Here is an outline of a few:
1 - Varroacides
There are three main chemical treatments for varroa which are easy to apply and can have high success rates of eliminating 95% of mites. They are Apistan, Bayvarol and Apiguard. Apistan and Bayvarol are plastic strips that you hang on the frames between brood comb, Apiguard is a slow release gel that you place on the top of the frames and it works by evaporation as well as contact and the bees eating it. Good practice is to alternate your treatments, this helps reduce the resistance that the mites build up to any one particular chemical. The best time to treat your bees is between harvesting honey and preparing your bees for winter. The aim of the treatment is to protect the last new bees who will over winter and start the colony going again in the spring. It's also a good to treat your bees in the spring, especially if you find that large numbers of mites have survived the winter. If not the mites are likely to increase in numbers rapidly with the increase in brood available.
2 - Drone Brood Removal
The mites prefer to lay their eggs in drone cells - so a good way of controlling their numbers is to put a brood frame in the hive with only a half strip of foundation at the top. The bees will build drone cells below this and once they are capped you can cut them out and destroy them. You can do this from April through to July when the bees will happily build lots of drone cells. This is good practice but is not effective on it's own.
3 - Open Mesh Floor
Some mites naturally drop of the bees and comb. If the hive has a solid floor these fallen mites can then climb back up onto the bees. The Beehaus has an open mesh floor which lets the mite drop safely outside the hive, from which they cannot return.
For more detailed information about varroa and for keeping up to date on treatments you should visit the Bee Base website for their helpful advisory leaflets