How does it work?
The cupric salts are administrated to the bees in form of syrup and work thereby as a systemic toxicant on the parasite: Varroas absorbing the bees’ heamolymph are asphyxiated, as the copper salts block haemocyanins (respiratory proteins responsible for oxygen transportation in the haemolyph of arthropods).
The mite show a high mortality rate (up to 96.5 %), but only after a delay of several days. Since the cupric salts are processed by the bees into the storage food, there are chances that also the mites in the operculated cells may be affected by the substance, while no notable effect have been observed on the bee brood. Cupric salts would thereby allow a median and long-term inhibition of the varroa mite without any notable disadvantage for bees. The researcher, M. Bounias, even claim a stimulating effects on bees.
Among different cupric molecules used, some show higher attractiveness to bees than others, which will have therefore an influence on the treatment’s efficiency: rates of consumption for the different syrups offered to the bees decrease in the following order: sucrose with cupric gluconate, sucrose alone, sucrose with cupric lactate, and sucrose with cupric sulphate.
According to Noirot, the treatment lack efficiency when a hive is highly contaminated, as a female mite may be able to lay eggs before the substance takes effect due to its delayed systemic effect, which will result in higher mite reproduction rate than death rate. This contradicts however Bounias’ speculation that cupric salts contained in the bee storage products may also affect the varroa larvae.
No toxicity is known for cupric salts in bees, even at high doses. However, the cupric salts have shown best efficiency at very low dose (1.5 g of cupric salt per litre of sucrose syrup), showing therfore a hormetic effect. No notable effect has been observed on brood either.
Among the copper salts used as anti-varroa treatments, cupric sulphate is a known irritant in humans. Other copper salts show only a very low toxicity and are sometimes used as fungicidal preservative in human food. Residues in honey are proportional to the dose that has been administrated to the bees. The highest residues show in intermediate products of honey and have volatized after one month, leaving no more residues than the natural copper levels in final honey.
Very easy: offered as syrup to the bees before the winter.
Bounias’ article dates back from 1993, while this idea does not seem to have found many followers: No further experiments and documentation are to be found in the Internet. However, Bounias’ death due to cancer only 10 years after his publication may be the actual reason why this idea has not been followed any further. Consequently, there is a lack of further empiric data that would confirm the efficiency and innocuousness for bees of this method.
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Bounias M. et al., 1993: Varroa jacobsoni control by feeding honey bees with organic cupric salts. http://www.beekeeping.com/articles/us/cupric_salts.pdf
- ↑ 2.0 2.1 Noirot E., 2000: The short-comings of anti-varroa methods. http://www.beekeeping.com/articles/us/anti_varroa_methods.pdf
- ↑ Wikipedia, 2012: Copper(II) sulfate. http://en.wikipedia.org/wiki/Copper%28II%29_sulfate#Toxicological_effects
- ↑ Petit J.-P., 2003: Michel Bounias est mort. http://www.jp-petit.org/nouv_f/bounias.htm