Mite infestation in the honeybee colony has a long-term impact on hive health

Mary O’Riordan describes one of the worse plagues to befall bees in this country in just over ten years since the negligent importation by some beekeepers of the deadly parasite — the varroa mite.

Mites and disease are not the most popular topics of conversation — however we need to talk about them at some stage.

Beekeeping was a relatively easy hobby, or business, prior to the arrival of the varroa mite, (Varroa destructor) which was discovered in Ireland in 1998 or thereabouts. 

As an Island we should have been able to steer clear of it, but during the past years the worldwide trade in honeybee colonies and queens has unwittingly introduced the mite into most countries of the world. 

The experience generally in bee colonies worldwide, is that the mite is in the country for some time before it is found, by which time it is widespread.

We have always had diseases, such as Acarine which effects the breathing apparatus of the bee, and nosema, a parasite which causes dysentery and we also have Brood diseases, American foul brood, and European foul brood. 

Putting the bees on new comb can help with nosema, but we don’t have any remedies for the others.

The varroa mite affects both adult bees and brood, but breeds only in the brood, the female mite is about 1.7 mm wide and 1.1 mm long, it is crab shaped, it has eight short legs and an oval brown shell covering all of its body and most of its legs.

Mite infestation in the honeybee colony has a long-term impact on hive health

The bees find it difficult to remove the mite by grooming because of its flattened shape, and the male mite is smaller. 

The females usually attach themselves to the underside of the bee’s abdomen and suck the bee’s blood by piercing the membrane.

The female enters a cell in the brood area containing a honeybee larva that is just about to be capped, she appears to prefer drone larva as they have a longer hatching period than the female worker, but will use a worker larva as well.

After the cell is capped the mite lays several eggs; they hatch and the resulting small mite larva feed by piercing the honey bee pupa and sucking its blood. In about seven days they are fully developed adults which go on to mate.

The honeybees that emerge after being infested with varroa are very much reduced in their value to the colony, and the number of viruses that have been discovered is frightening — one such is deformed wing virus, the bees emerge from the cells with malformed wings.

I have seen this for the first time last year and again this year, The increase in the mite population inevitably means that the colony will, in time, be wiped out without careful management by the beekeeper. 

Colonies are usually doomed once they are infected by the mite.

Treatments for the mite are fairly straight forward , but time-consuming. Most beekeepers now use mesh floors instead of solid floors and an insert can be placed under the mesh and the mite drop can be monitored especially after treatment, the mite drop this year was huge.

There is a choice of treatments available and authorised by the Department of Agriculture, such as Bayvarol, (which was one of the easiest to administer, but has now more or less lost its effectiveness, as the mite has become immune to it); Apigard which is thymol based, and Maqs which is formic acid based, (formic acid is a natural ingredient of honey).

These are the treatments most used now — and all are of course, administered after the honey is taken off.

Until the advent of Varroa, beekeepers had a restful period in autumn and winter, but we now do a winter treatment as well, so we open our hives in late December/early January, when the hives are bloodless, and trickle a light dose of Oxalic Acid (found in Rhubarb) over each seam of bees, which is harmless to the bees, but kills any mites. 

The treatments and control of varroa will continue to evolve with time and experience.

Upcoming events:

Fota Honey Show, Sunday October 4, at 2pm, at the Education Centre Fota Wildlife Park. Worth a visit especially if you have never been to a Honey Show.

County Cork Association is having beginner’s classes starting on the October 14; you need to apply online at 


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