PUBLIC ENEMY NO.1

If you keep bees, sooner rather than later you will become aware of a particularly nasty character known as Varroa destructor. This parasitic mite is aptly named, and varroa is the bane of many a beekeeper’s life, as well as being a real problem for honey bee colonies. It is one of THE drivers of global honey bee health decline, and so cannot be ignored. Alongside being vigilant for various diseases, beekeepers need to monitor mite levels within their hives at regular intervals in order to manage and control mite infestation.

The varroa is a crab-like mite that pierces the skin of adult and pupating bees. It was thought to feed on the haemolymph (roughly the equivalent of blood in an insect), but recent research, led by Samuel Ramsey, PhD, is now leading scientists to believe it is the fatty body of a bee, similar to the liver in mammals, that the mites are seeking. This breakthrough in understanding more about the mites is key to working out ways to combat them and much research is underway around the globe to perhaps find something that makes that fatty tissue taste terrible and help the bees!

The mites are particularly dangerous because they act as vectors for disease organisms, particularly viruses. A lot of viruses can be found in bee colonies but they rarely threaten them; however, varroa can trigger viruses into activity and that’s when serious problems, even colony death, occur.

Adult mites latch onto adult bees and are transported into the hive where the pregnant female mite finds her way into a brood cell containing a young larva. She stays hidden in the cell, feeding on the pupating bee, safe under the wax cap. Several mites then hatch, one male with up to four females which then mate, and pregnant mites exit the cell on the adult bee when it hatches. One mite going in and up to five mites coming out, on the majority of bees that are hatching, tells us that very soon the mite numbers will have increased to an unsustainable level.

One of the most obvious viruses transferred by the varroa mites to bees is deformed wing. This is exactly how it sounds – the bees hatch with shrivelled or non-existent wings. The affected bee can carry out some jobs within the colony but will never become a forager, and if there are too many bees with this virus then the colony will slowly starve.

As involved beekeepers we do need to monitor the levels of mites in our hives, and we do this by firstly assessing the scale of the problem by carrying out a simple mite-drop count. A removable tray is inserted under the mesh floor of the hive and 48 hours later it is removed and the number of mites is counted and compared to a published table that enables us to assess whether we need to treat the colony or not.  Clearly there will be more mites in the height of the year simply because the number of bees in a colony is greater than in the depths of winter, we some common sense is required when reading from the tables!

The range of treatments available is wide and varies in both chemical makeup and price, plus there are less invasive and more natural ways of fighting varroa. For instance, all of our hives contain a BeeGym, a small plastic tray kitted out with flippers and pieces of nylon with which the bees groom themselves, knocking off the mites as they do so. Several treatments are based on thymol which is effective in killing mites, and some use oxalic acid, which is often used when the colony is broodless ie in winter. All treatments come with extensive instructions which must be followed to the letter (paying particular heed to upper and lower temperature parameters) otherwise the onset of resistance to the active ingredients may be hastened, rendering the treatment useless. And in the worst case, if it’s too warm the treatments can harm the bees themselves.

It’s not for us to dictate how or when, or indeed if, you treat your colonies for varroa but we do advocate that you monitor the levels and do what’s best for your bees.