Resistance of Varroa to Medicaments used in Iran
Varroa was first found in Iran in the 1980s and for two decades Iranian beekeepers have had to deal with this mite. Various treatments were evaluated and Apistan became the most popular. However, in 1996 their problems worsened when Apistan-resistant populations of varroa emerged.
The parasitic mite Varroa destructor is well known to beekeepers because in many countries it is the most common cause of death of Apis mellifera colonies. It was first found in Iran in the 1980s, and we have been faced with this problem for over two decades. Methods of controlling the mite have been investigated and several products are now approved for use. A recent difficulty in Iran as well as in other countries has been the development of resistance in varroa to tau-fluvalinate (Apistan). This has led to a high mortality of colonies worldwide, and we have therefore investigated various new control products on sale.
The Ministry of Agriculture in Iran purchased treatments for varroa infestation from different firms (Ciba Geigy, Bayer, Sandoz, Farmak-achim, Alvetra, Vita Europe, Elanco), in order to test their action on the parasites and the effectiveness of different types of treatment: by inhalation (fumigation), absorption (systemic action) and contact. Varroa infestation in Iran is serious, and table 1 lists the results of the treatments. Beekeepers must learn to live with it: they should maintain only strong colonies, requeen them every two years, and rear queens selected for their resistance to diseases. If these rules are followed, the colonies will not be endangered by the varroa mite.
Since 1996 it has become apparent that varroa is resistant to Apistan, probably for the following reasons:
- Since 1989, Apistan has been the principal treatment used in Iran.
- Fluvalinate is liposoluble, so residues are left in beeswax combs and accumulate progressively as the wax is reused for comb foundation.
- The wax of continuously used comb contains only small amounts of the active compound.
- Wooden frames impregnated with Klartan (phytosanitary formulation) are used..
Recently use has been made of thymol, which is the active component of Apilifevar and Thymovar as well as Apiguard. In 2000 and 2002 I tested Apiguard, and also studied many publications from around the world. Thymol has the advantage of being a natural substance, and one with a low toxicity to humans. Also, Varroa destructor has not been reported as resistant to it. However, the use of Apiguard has the following disadvantages:
- Colonies must be given a double dose, and the treatment repeated in the autumn. Mites that survive the first treatment reproduce during the bees’ active season. So it is necessary to use another acaricide.
- When colonies infested with varroa were treated only with Apiguard, they showed abnormally high winter losses, with clear evidence of mites.
- A strong odour is apparent during the three days following treatment, which disturbs the colony and stimulates the bees to clean their hive.
- For two applications the treatment takes 14–16 weeks, which is inconvenient for the beekeeper.
- It is necessary to provide a space between the top of the frames in a hive and the hive roof, for instance by inserting an empty super; this reduces the temperature of the bees and increases their honey consumption.
Temperature variations during the treatment are important. If the temperature is above 35° C, the treatment is more effective (< 70%) but causes a higher larval mortality. If the temperature is less 12° C the treatment is less effective (< 60%), and leads to a higher mortality of adult bees.
If proper conditions for its use are adhered to, thymol residues do not increase. Whereas Apiguard is ineffective against Acarapis woodi, both menthol and formic acid were found to be effective in tests at four sites in the Department of Gillan in north Iran during 2001 and 2002.
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- Baggio A; Piro,R; Crivalleri.D; Dainese N; Damolin O; Mutinelli F (2002). Prodotti a base di timolo per il controllo della varroasi.studio dell'efficacia e dei residui nel miele, L'Ape nostra Amica (4):30-34.
- Shahrouzi R, 2001 - Two decades of living with varroa in Iran. Apimondia Durban- South- Africa, 28 Oct to 1 Nov.
- Shahrouzi R, 2003. Against varroa in Iran. Having an AMM control in six Departments, Apimondia Ljubljana, Slovenia, 24 to 28 August.
- Shahrouzi R, 2001.Tests de terrain effectués en Iran sur les nouveaux produits anti-varroa, Bulletin Technique Apicole 28(2) 73-76.