The Varroa Mite: A Devastating Honey Bee Parasite

The Varroa mite, also known as Varroa Destructor, is a modern honey bee plague.

It’s capable of completely wiping out a honey bee colony, and is responsible for the loss of massive numbers of colonies in recent years.

Aptly Named…

The scientific name of this creature, Varroa Destructor, is very appropriate.

Not only has Varroa wiped out many managed colonies, it has also reduced the feral bee population (wild bees) to nearly zero in many areas.

Have you heard of the neutron bomb?

This bomb was designed to release huge amounts of radiation while minimizing the destructive explosive force. The idea was to kill people, but minimize damage to infrastructure – buildings, bridges, roads, etc.

The Varroa mite could be thought of as the neutron bomb of honey bees.

Varroa has been very effective at virtually wiping out honey bee populations in a given area, while leaving other insect species unscathed.

What Exactly Is A Varroa Mite?

Varroa mites are parasitic predators of honey bees. They attach themselves to a honey bee, and feed upon the bodily fluids, like a tick. The mites are very small, about the size of the head of a pin.

In the photo below, you can see an adult Varroa mite (reddish-brown colored) on a brood comb, close to a young bee emerging from its cell.
varroa mite on comb of honey bee brood

Female mites lay eggs in brood comb cells containing honey bee larvae. The eggs hatch and attach themselves to the developing bees after the comb has been sealed.

The parasitic mites shorten the lives of the host bees, but not only through the direct effects of parasitising the bees. It’s been found that there are also several debilitating viruses that are transmitted through Varroa.

These viruses can cause problems such as deformed wings, rendering bees unable to fly.

Varroa Mite Control

There are a number of options available to beekeepers for keeping Varroa mites under control. By ‘under control’ I mean keeping the mites to manageable levels – it can be very difficult to entirely eliminate them.

Chemical controls are available, and have been for a number of years. But there are some potential drawbacks to using chemicals, even when the chemicals are used according to label instructions. And unfortunately, chemicals aren’t always used per label directions.

One problem that has occurred with the use of chemicals is that the mites have developed a certain degree of resistance to some of the chemicals. Chemicals that were once very effective against the mites can become less effective over time.

Another drawback to using chemicals is the risk of contamination to honey if proper procedures haven’t been followed, and a likelihood of a certain amount of chemical build-up within the wax combs of a hive.

But in spite of the drawbacks to using chemicals, they can be effective.

The decision of whether to use chemicals has been difficult for some beekeepers. Do you treat your hive and (hopefully) ensure its survival, or do you avoid chemicals and let nature take its course?

Though generally not as effective, there are some alternative mite treatments that do not involve the use of chemicals. These include:

Trapping Mites in Drone Brood

Female Varroa mites prefer using drone brood over worker brood for the continuation of their life cycle. Beekeepers can use this preference to their advantage by increasing the amount of drone brood in a colony, and then removing and destroying the drone brood after it has been capped. The mites that infest the drone brood are, of course, also destroyed. This process is unlikely to eliminate Varroa in a colony, but it can effectively reduce the population of mites, at least temporarily.

Screened Bottom Boards

It’s normal for some mites in an infested colony to fall to the bottom of the hive. If the hive bottom is solid, the mite can make its way back to the brood nest where it continues its destructive behavior. But screened bottom boards have been designed where the grid of the screen is large enough that most of the mites fall through, but large enough that bees have no difficulty walking on the screen.

So when a mite falls from the brood area, it falls through the screen into an oil reservoir or a sticky trap from which the mite can’t escape, and it eventually dies. A screened bottom board can help to reduce the mite population to a degree, and can also be an effective tool for monitoring the level of infestation within a colony.

Dusting With Sugar

Dusting the bees with powdered sugar will cause the bees to clean themselves and each other. In the process of cleaning, or grooming, many mites are dislodged and fall off the bees’ bodies.

When sugar dusting is done while using a screened bottom board, the mites that fall will be trapped. This treatment, too, will not eliminate mites, but it can make a nice dent in the population. There’s no harm to the bees (they eat the sugar), so this treatment can be repeated often.

Survivor Bees and Russian Bees

Varroa mites first became a major problem in the U.S. in the 1980’s. The devastation has been extreme, particularly among feral colonies that were not managed by beekeepers, and therefore received no treatments for Varroa.

And though feral colonies have been all but wiped out in some areas, they weren’t entirely eliminated. Some survived. These bees have a genetic ability to handle Varroa infestations and are called survivor bees.

There are also survivor bees among managed colonies. That’s because some beekeepers, and even some large-scale bee breeders, have chosen not to treat their bees for Varroa.

They willingly accepted losses – sometimes huge losses – to try to build a population of Varroa resistant survivors.

Their efforts have been successful, because there are strains of bees available now for which ongoing, continuous treatments aren’t necessary.

That doesn’t mean that these bees will survive long-term, year after year after year. But it does mean that it’s possible to keep bees without methodically treating for Varroa, and not be virtually wiped out every year.

The oldest survivor bees are from Russia. Varroa Destructor is thought to have struck first in this area, and so those bees have had more time to develop genetic resistance to Varroa.

The result is that these bees, while not impervious to Varroa, do tolerate it better. Many queens of this strain have been imported to the U.S. (and other Varroa-stricken areas) and are available for purchase by beekeepers.
It’s Been A Rough Few Decades…

Though the Varroa mite has been absolutely devastating throughout much of the world, there is some light at the end of the tunnel. Survivor bees and non-chemical treatments are having an impact.

Long term, the hope is that Varroa resistant strains of bees will allow beekeepers to manage the Varroa mite without reliance upon chemicals, and without significant losses.

And at this time, that appears to be a very realistic hope.