3 minute read

Varroa - How to control it

During the last 20 years, the Varroa mite has destroyed wild populations of Apis mellifera honeybees and has threatened beekeeping industries. Scientists have undertaken spectacular amounts of research on the mite, and how to control it. In many ways the mite has revitalised honeybee research and stimulated funding and employment. But we still have no final answers on how to control Varroa.

The best answer would have been for beekeepers not to continue moving infested honeybees from one country to another.

There is no single method that is totally effective in controlling Varroa.

Smite the mite with smoke

Beekeepers have a long established practice of using smoke to calm their bees before opening the hive. Now US Department of Agriculture scientists have found another protentional benefit from smoke - when burned some plant smokes give off natural chemicals that control honey bee mites   

The standard method of Varroa treatment in the USA is using fluvalinate Fluvalinate is synthetic pyrethroid which is harmless to bees, but cannot be used whilst bees are producing honey otherwise the honey becomes contaminated. A further problem with fluvalinate is that the mites can develop resistance to it. Alternative control mechanisms are being investigated.

Dr Frank Eischen hafound that smoke from certain plants either kills Varroa mites or causes them to fall off the bees. 300-400 mite infested bees are put in a cage and the cage is covered with plastic container. The smoke from the trial plant is puffed into the container which is then corked to prevent the smoke escaping. 

After 60 seconds the bees are removed and placed over sticky white card to catch any mites that fall off the bees. So far Dr Eischen has tested smoke from about 40 plants. 

The first smoke Dr Eischen tested was from the ‘creosote’ bush, following a recommendation by Mexican beekeeper, David Cardoso. The creosote bush is native to Mexico and Texas.

Creosote bush smoke achieves 90-100% mite knockdown after one minute but excessive exposure to the smoke harms the bees.

“It is hard to find chemicals that remove mites without harming bees”, says Dr Eischen. “Grapefruit leaves however fit the description. After 30 seconds smoke from the grapefruit leaves knocked down 90-95% of the mites”.

Few of the mites are actually killed, most simply fall off the bees. “Either the smoke chemicals irritate or confuse the mites”, says Dr Eischen, “no-one is certain”. “But the good thing is that the leaf smoke does not seem to have any detrimental effects on the bees at all”. 

Dr Eischen is not recommending that beekeepers try these methods of control yet. “These findings are still preliminary and the active chemicals in the smoke are not yet identified. What we are trying to do is isolate and identify the chemicals which are acting as miticides” he explains.

This information is taken from an article written by Sean Adams in Agricultural Research, August 1997, kindly provided by Dr Darrell Cox  of Echo Inc.