Inert Dusts

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Inert Dusts

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How does it work?

Varroa is able to adhere on the bee's body thanks to suckers with which its legs are equipped. If fine dust comes under the suckers, the mite loses grip and falls. Varroa is not either able to move on a surface covered with fine dust.[1]

Several fine dusts have been experimented: flour, pollen, mineral dust.[2] The best-documented study has been performed by Fakhimzadeh of the University of Helsinki with confectioner sugar.[1]

Efficiency

Fakhimzadeh[1] has experimented two methods of confectioner sugar dusting into the hive:

  1. 5 g of sugar in direct dusting, and
  2. 0.5 g of sugar in aerated dusting.

The first method allowed a varroa knockdown of 91% and the second of 62%.

According to the manufacturer, the particle size of the sugar used for the experiment is comprised between 25 and 40 µm), but the study revealed that the presence of particles under 5 µm were decisive for varroa knockdown.

Supplementary physical treatments (shaking, etc.) as well as pre-anaesthetisation of the bees with CO2 (with the assumption that bees might inhale the sugar with harmful effects) remained without influence on the treatment's efficiency. Pre-anaesthetisation even revealed to have an adverse effect on the bees' health (high mortality 5 days after anaesthetisation).

Risks

No sugar dust was found in the respiratory system of the bees on dissection right after the treatment and 48 h after first grooming. The bees therefore do not seem to inhale the dust. The study needs to be repeated for confirmation and refined.

Fakhimzadeh's reports high bee mortality after some trials without anaesthetisation, nevertheless essentially in the most contaminated colonies. Since no dust contamination has been detected in the bees' respiratory system, this was ascribed to an other factor (a plausible reason could be e.g. a weak hive health due to a strong infestation).

Trials on field yielded similar results to the laboratory trials.

Fakhimzadeh reports that bee mortality is generally lower in colonies treated according to this method than in untreated colonies.

Practicability

This method may require special equipment.

Flour and mineral dust may contaminate the hive and the honey with non-toxic, but unwanted material. The presence of dust will add supplement work for the worker that will want to clean up the hive after dusting. Pollen may be difficult to harvest by the beekeeper in sufficient quantity, especially in stressed conditions. Dusted sugar should have low effect on the quality of the honey, particularly with the low doses prescribed by Fakhimzadeh and if the treatment is not too frequent.

Further advice

The treatment should preferably performed by a specially trained vet able to determine the adequate dose and treatment frequencies.

It can be best combined with the bottom screen method to prevent the mites from climbing back into the hive. Dusts can also best be used instead of grease or a sticky substance on the surface of the bottom board since the mites are not able to travel on a dusty ground.

The method may be also interesting for the control of varroa control in bee commerce e. g. as a customs control before importing into the European Community (see also the Norms & Legislation section on this topic) in order to restrict pest spreading.

As with smoking, the inert dusts promote an intensified grooming behaviour in bees.

References

  1. 1.0 1.1 1.2 Fakhimzadeh K., 2001: Detection of major mite pests of Apis mellifera and development of non-chemical control of varroasis. University of Helsinki, Department of applied biology. http://ethesis.helsinki.fi/julkaisut/maa/selai/vk/fakhimzadeh/detectio.pdf
  2. Ellis M., 2001: Using Inert Dusts to Detect, Assess and Control Varroa Mites in Honey Bee Colonies. University of Nebraska, Department of Entomology. http://www.epa.gov/pesp/regional_grants/2001/r7-2001.htm




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