|Resistance of varroa to
medicaments used in Iran
by Reza Shahrouzi
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:
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:
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.