Return to Health

Varroa

Varroa weakens honey bee colonies decreasing honey production, heavy infestation may even result in absconding. This parasite is found throughout the world, except for Australia and parts of New Zealand.

It is endemic in the UK with most hives seeing signs of the parasite sometime in their lifetime.

This reddish-brown mite is about the size of a pin head and is easily visible against a light background. Mated female mites move into brood cells with older bee larvae. Drone brood are preferred, but worker brood are also infested. Mites will feed on the larval food or puncture the larval body and feed on the bee’s blood. A “mother” mite may lay an egg every 36 hours on the side of a cell. The first egg usually hatches into a male and stays within the cell. The other eggs hatch into females and feed and grow within the cell. Next, they mate with the male and emerge from the cell when the bee emerges.

Varroa is endemic across Moray so if you keep bees here you can be sure that they will be infested with the varroa mite. But that shouldn’t give you cause to panic! Beekeepers should be aiming to keep the varroa mite below the level where they cause significant harm (that’s officially less than a 1,000 mites per colony in the U.K.) by using a combination of controls, at different times of the year. The bees, with a little help from the beekeeper, can learn to live with varroa, but, if the beekeeper does nothing to tackle varroa it is more than likely that the colony will die out within a year or two.

Even if the bees were treated for varroa last autumn, the mite can build up quite rapidly as the Queen increases her laying rate and if left untreated can lead to sudden colony collapse later in the summer. Remember this – with an 80% kill rate the danger level (of 1,000 mites) is reached again in only 65 days and with 90% in 100 days!

Also, there are now pyrethroid resistant mites in Scotland so it is unwise to simply rely on a varroacide like apistan.

Impact

Varroa feeds directly on honey bees causing injury; the female sucks the blood of bees by piercing the body of the bee at the soft intersegmental area. However, only in extreme infestations are adult bees severely harmed. If brood are infested by more than one Varroa in the brood cell deformation of the brood occurs especially in the abdomen or wings. Impact from infestation by only one mite in brood may not show visible signs but its life span will be shortened and behaviour affected.

Bees and Brood infected by Varroa with be considerably weakened and more susceptible to other diseases, in fact the Varroa may even transmit other diseases through its penetration of Honey bee bodies.

Colonies if left untreated may die within a 2-3 year period, and Varroa may be spread to other hives or apiaries by transient bees, affecting a wide area.

How do I spot it?

Late stage, heavy mite infestation can be seen by deformed adult bees crawling on combs or near the hive entrance.

Other methods may be used to detect mites. Direct sampling opening of older larvae/pupae brood cells, especially drone cells. So what simple steps can the beekeeper take now to attack varroa? The ardent Beekeeper should check the varroa infestation level in spring time and during summer and into autumn, by counting the dead mites on the floor of the hive over a given number of days (open mesh floor and insert required), or, by uncapping drone brood and looking for the mite there.

Very roughly, if more than 5-10% of drone pupae are infected, then the infestation is serious, and urgent treatment is required – seek advice if necessary.

Regardless of whether you have the time or inclination to measure the varroa levels in your colony, DRONE BROOD REMOVAL is a very simple way of fighting back against varroa, it doesn’t require a high level of skill and is something you should be doing now up to the end of July!

How does it work? Well, varroa prefer to lay eggs in drone brood due to the extra days it takes for drones to emerge from the cell (they can make more babies) and beekeepers can take advantage of this. Simply insert a shallow frame of drawn comb or foundation in the middle of the brood chamber, and invariably, the bees will build drone comb on the underside of the frame. Once the queen lays in this comb the varroa will move in and once it is sealed, the sealed drone brood, along with the varroa mite inside the sealed cell, can be cut away and disposed of. The shallow frame can be immediately replaced in the brood box and the entire procedure repeated again and again. It is very important not to let the drones emerge because if this happens the beekeeper is actually making the situation worse rather than better!

The colour of the dead brood can be off white, light-dark brown and is soft to touch.

Impact of Disease

Older larvae or pupae start to die
Greater numbers of dead brood throughout the colony
Neighbouring colonies affected
Outward spread to other apiaries

Sources of Disease

Contaminated second hand equipment
Contact with bees from other hives
Beekeepers transferring spores from hive to hive
Honey from foreign hives with disease

Sugar Dusting for Varroa

Earlier we looked at a simple step to attack varroa by encouraging the bees to build drone brood which the varroa prefer, and then when the sealed drone brood is removed the varroa and her offspring inside the cell are removed too. To compliment this we need to also attack the mites that live on the adult bee and we can do this by dusting the bees with icing sugar. Drone brood trapping and sugar dusting is an excellent method of controlling varroa in your hive, attacking the mites in the brood whilst also knocking them off the bees.

Why does sugar dusting work and how do you do it and will it harm my bees you may ask? Well, the sugar dust adheres to a mite’s foot pads causing it to lose its grip on the bee and dusting may also stimulate bee grooming behaviour. It is a mechanical method of mite control rather than chemical. It does not directly kill the mites – they fall out of the hive and can’t return.

It’s safe, doesn’t hurt the colony, can be used even when they are storing honey, works any time of the year that bees are not tight in a cluster, is cheap and only takes seconds. The drawbacks are that its application is dependent on fair weather and it may also draw ants into the hive.

Here’s how to do it. The equipment needed is a bee brush, a 1 cup measuring cup filled with icing sugar, a wood rimmed travelling screen, and the colony should be on a screened bottom over an open mesh varroa floor.

Technique: Smoke the colony, remove the crown board and smoke the bees down off the top bars. Put the travelling screen over the frames and then use the cup to spread the icing sugar on the screen over the bees (some beekeepers don’t use the screen and apply the sugar direct onto the top bars). Then use the brush to sift the sugar through the screen and onto the bees. Lift the screen and continue to use the brush across the top bars so that the sugar falls between the frames. Replace the cover.

Mites will begin to fall within seconds and if you have rubbed Vaseline on the floor insert you can get a good indication of your mite level in an hour.

It is claimed that if you dust once every 4 weeks and continue Drone Trapping the varroa mite population will be held in check!

top of the page

Share