Smoking is a practice that have been established for centuries in beekeeping to calm the bees and reputed non-damageable for the bees.
Several smoking tests with medicinal plants have been performed as a method to fight varroa. Tested plants comprise tobacco, different species of thyme, harmel, walnut leaves, mint, etc. F. Eischen, researcher at the US Department of Agriculture, has tested the effect of smoking with over 40 plants.
How does it work?
Nevertheless, smoking performed with herbs that have a toxic effect, like tobacco (see, e.g., the study by Shaddel-Telli A.-A. et allii cited below), can have varroa kill as a supplementary effect.
A study performed in Iran by Shaddel-Telli A.-A. et allii in 2008 compares the effects of smoking with powdered tobacco, thyme (Thymus kotchyanus) and harmel leaves and spraying extracts of the same plants. The authors stated that tobacco extract vaporisation allowed a substantial reduction of infested beehives (83.6%), followed by thyme smoking (36.51%), without obvious harm for bees.
As far as smoking with tobacco leaves is concerned, witnesses are most diverse. The study by Shaddel-Telli A.-A. et allii does not demonstrate a convincing efficiency (reduction of infested hives by only 8.46%), as a contrast, another study performed in Iraq showed that bees population treated with tobacco smoke were more populous and noticeably more active, however, the report does not mention any digit or dose that would allow any comparison.
The study performed by F. Eischen could bring two herbs into light showing particular efficiency in knocking down the parasites after one minute without obvious harm on bees: cresote bush, a plant native to the South of the United States and Mexico, with a knockdown rate of 90-100% and grapefruit leaves, with a knockdown rate of 90-95%.
Generally, according to the witness of beekeepers, bees recover, after some short disorientation, recover rather well of smoking.
A similar study to the one performed by Shaddel-Telli A.-A. et allii mentioned in their report showed that smoking with powdered thyme could result in high mortality in bees, nevertheless another thyme species (Thymus vulgarus) had been used for that study, which suggest that thyme toxicity in bees can vary from species to species and that the medicinal plants used for smoking have to be chosen very carefully to avoid harmful effects on bees.
Unfortunately, the study by Shaddel-Telli A.-A. et allii does not specify how the tobacco extracts had been manufactured, nor their nicotine and other toxic alkaloids concentration. Nicotine is also used in agriculture as a pesticide and it has long been common, in agriculture and gardening, to spray "home-made" tobacco extracts on plants. As those extracts are contact poisons that are equally highly toxic for animals and humans, even if nicotine degrades relatively fast in the human body and bees seem to show a resistance at low doses (<5 ppm), the use tobacco extract is not acceptable in organic beekeeping. Moreover, varroa could very well develop a resistance to nicotine as it did against other pesticides.
Several smoking processes may be necessary for sufficient remediation and the effects of long-term and repeated application are still unknown. In addition to the deposition of toxic substances, it is known that smoke interferes with the bees' pheromones. The effects that frequent smoking can have on the cohesion of a superorganism as a bee colony can be for the moment only a subject of speculations. The dosage of the smoking powder and the duration of the treatment may require much experience and expertise to reach a maximum of efficiency with a minimum of harm for the bees. These aspects could also explain the discrepancies in success among the different studies and witnesses quoted above.
Finally, repeated smoking could leave residues in the hive that could affect the honey's quality.
Despite of these reservations, smoking remains an interesting prospect, since it could contribute to promoting in Apis mellifera an evolutive defence mechanism against varroa comparable to Apis cerana's.
The method is easily put in practice with the custom equipment of a beekeeper.
Only herbs from organic agriculture should be used to avoid unwished deposition in the hives and the honey of toxic substances like nitrates and phosphates from fertilizers and pesticides typically found on plants from industrial agriculture.
The method needs more trials and refining to determine healthy exposure times, application frequencies and dose concentrations for bees. Once refined and confirmed, the treatment should be performed by a specially trained vet. As a beekeeper, do not try the method by yourself!
The method can be best combined with the bottom screen method to prevent the mites from climbing back into the hive.
- ↑ 1.0 1.1 USDA, 2007: Smoking Out Bee Mites. United States Department of Agriculture, Agricultural Research Service, 2007-07-02. http://www.ars.usda.gov/is/AR/archive/aug97/mitesmoke0897.htm
- ↑ 2.0 2.1 Sanford, M.T., 1997: Smoking Bees: Alarm and Varroa Control. University of Florida Department of Entomology and Nematology, August 1997.
- ↑ 3.0 3.1 BeeSource, 2008: Tobacco and Varroa. Beesource Beekeeping Forums > General Beekeeping Forums > Diseases and Pests. http://www.beesource.com/forums/showthread.php?t=218077
- ↑ 4.0 4.1 4.2 Shaddel-Telli A.-A. et allii, 2008: Using Medicinal Plants for Controlling Varroa Mite in Honey Bees Colonies. In: Journal of Animal and Veterinary Advances 7 (3): 328-330, 2008. ISSN: 1680-5593. http://www.medwelljournals.com/fulltext/java/2008/328-330.pdf
- ↑ Behnam O., 1999: Use of tobacco smoke against parasitic mite syndrome. Bees for Development. http://www.beesfordevelopment.org/info/info/disease/use-of-tobacco-smoke-agai.shtml
- ↑ Kreuter M.-L., 2001: Pflanzenschutz im Biogarten: Der Garten-Klassiker für die naturgemäße Abwehr von Krankheiten und Schädlingen. BLV Verlagsgesellschaft, München. ISBN: 3 405 15980 6
- ↑ Singaravelan N. et allii, 2006: The Effects of Nectar-Nicotin on Colony Fitness of Cage Honeybees. Journal of Chemical Ecology, Vol. 32, No. 1, January 2006. http://research.haifa.ac.il/~minbar/Sing%20et%20al%202006.pdf