VARROA - WHAT IS IT?
Varroa is a parasitic mite of honeybees. The tiny mite lives and feeds on larvae and adult bees.
Latin name: Varroa destructor
Size: The female has a diameter of about 1 mm. Male mites are much smaller.
Appearance: Female - shiny, red-brown and elliptical in shape with four pairs of legs. Male mites are white in colour and spend their lives inside capped brood cells.
It may take three or more years before there are sufficient numbers of mites present in a honeybee colony for them to be detected. If one colony in an apiary becomes infested with Varroa, all colonies in the apiary will become infested.
VARROA - WHERE DID IT COME FROM?
Varroa jacobsoni was first named in 1904 by Dr Oudemans in Indonesia. He identified it on one of the Asian honeybee species, Apis cerana. This species is the natural host of Varroa: the bees and the mites have developed a host-predator relationship which allows the continued survival of both species. In the long term, it would not benefit the mites to completely wipe out their host species.
Our current problems with Varroa in Apis mellifera colonies began when humans moved European Apis mellifera into Asia. Varroa mites spread from Apis cerana colonies into Apis mellifera colonies.
Unlike Apis cerana, Apis mellifera has not evolved in the presence of the mite. Therefore Apis mellifera has not developed any defence mechanisms against Varroa. Colonies of Apis mellifera can be completed destroyed by the mite, unless the beekeeper takes some action to control mite numbers.
The effect of Varroa on Apis mellifera is not always the same. For example in Central and South America, some populations of Africanized honeybees seem able to survive in the presence of the mite. The effect of Varroa infestation is also somehow related to the viruses carried by the mites and honeybees.
VARROA - WHERE IS IT NOW?
Movement by humans of colonies of Varroa-infested Apis mellifera led to the spread of Varroa around the world. In 1987 Varroa was found in the USA, in 1990 it was found in Canada, in 1992 it was found in the United Kingdom.
VARROA - IN SOUTH AFRICA
Varroa has been confirmed present in sub-Saharan Africa. It was identified in the Western Cape, South Africa in August 1997.
GAUTIER, D (1997) South African Bee Journal. 69: 2
LEAR, E N (1998) Personal communication
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. The following two articles introduce new methods of control currently being investigated.
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 potential benefit from smoke - when burned some plant smokes give off natural chemicals that control honeybee mites.
The standard method of Varroa treatment in the USA is using fluvalinate. Fluvalinate is a 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 has found 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 a 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 a Mexican beekeeper, David Cardoso. The creosote bush is native to Mexico and Texas.
Creosote bush smoke achieves a 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.
SPICE THE MITE WITH NUTMEG
by Jorge Murillo-Yepes, B&D’s Correspondent in Grenada
In BfDJ 43 and at the Apimondia Congress in Antwerp, Jorge Murillo-Yepes spoke about the control of Varroa using a locally produced mixture including nutmeg oil. In this article he explains current, exciting progress.
A research programme has recently started in the Caribbean island of Grenada to validate the efficacy of essential oils as miticides. We are placing special emphasis on locally-produced oils: cinnamon, clove, mace and nutmeg. We are considering the possibility of offering a commercial ‘apimiticide’ made from Grenadian coconut oil, Grenadian beeswax and Grenadian nutmeg oil. It sounds really nice!!
Do not accuse us of putting on the saddle before bringing in the horse! I must explain that this essential oil cream treatment has been used by the beekeeper who first reported Varroa present in Grenada. He has found high levels of Varroa casualties, and importantly a lack of any noxious effects of the treatment on the bee colonies. Also the number of worker disabilities resulting from the viruses vectored by the mites has been reduced almost to zero. Quite a relief from the pitiful sight of thousands of crippled, crawling bees of recent times.
The ‘Magic’ Formula is:
450g coconut oil (or any vegetable cooking oil)
15g essential oil (we have tried eucalyptus, nutmeg, peppermint and spearmint)
1. Break the beeswax into small pieces.
2. Melt in a double boiler (a large pot with water containing a small pot with the wax) with the coconut oil.
3. Stir until the wax melts completely and allow to cool to 42-45°C. If a thermometer is not available, cool until the mixture just starts to harden at the surface, but is still quite fluid.
4. At this point stir the essential oil into the mixture until thoroughly blended.
The above mixture should be sufficient for 50 hives if applied as follows:
1. Cut strips from any of the following: bamboo, Bristol board, cardboard, plastic containers, plywood, or tins. The strips should between two and five cm wide by 20 cm long.
2. On one side of the strip spread one or two teaspoons of the miticide mixture, distributing it evenly.
3. Leave a 1 cm section at each end of the strip clean to avoid getting it on yourself.
4. Push the strip deep into the entrance of the hive undergoing treatment, preferably before 0900 hours on a hot, sunny day. If Varroa is present, the first effects of the treatment (dead or terminally ill mites on the bottom board) can be seen within 2-4 hours. Presumably the hotter and drier the weather, the faster the effects.
5. After 24 hours (longer for lower temperatures), the treatment is over and a number of dead Varroa can be seen under the brood chamber. Also, and possibly for the first time, white males can be observed dead on the bottom board or groggily walking about in a totally uncharacteristic behaviour (normally his whole life takes place within an invaded brood cell).
We have not yet carried out trials to determine the best time during the bee calendar for these treatments. However we have made the following assumptions:
1. Due to the natural (as opposed to man-made) nature of the active control ingredient, the risk of obnoxious contamination of hive products is negligible.
2. Essential oil treatments for parasitic arthropod control in honeybees does not negatively affect colonies or individual bees, in their physiology or exchange of pheromones.
Based on these assumptions, and with due regard to the local climatic and floral characteristics of the apiary and foraging area, beekeepers would be well advised if they apply essential oil treatments against Varroa not less than one month before the main nectar flow. This is as a general sanitary practice.
Emergency treatment would be advisable in cases of extreme infestations, manifested by direct observation of Varroa in capped drone cells, dead mites on the bottom board, proliferation of handicapped workers and drones crawling in and out of the hives and general colony ‘demobilisation’, with a consequently sharp decrease in honey production and pollen gathering.
It has been our experience that even colonies considered beyond redemption can be saved by these treatments if applied to populations of more than 10,000 bees. So far we have not had any losses of colonies due to severe re-infestation, as the treated hives have been able to achieve self-reliant populations.
The October-November 1997 rainy season was the driest I have seen in 20 years in Grenada. We have concluded that during periods of heavy rain bee colonies in tropical conditions are at their weakest point in terms of resistance to Varroa infestation and proliferation. Therefore, we have seriously considered advising treatment prior to the onset of the rainy season.
As you can appreciate, our smiles continue to widen when we think about the future of beekeeping in Grenada, as far as Varroa is concerned.
[Bees for Development Jounal #46]