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Organic chemicals in varroa control 2003 http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleForFree.cfm?doi=b301510f&JournalCode=POKlaus Wallner1 from Universität Hohenheim in Stuttgart, Germany and Ingemar Fries2 from the Swedish
University of Agricultural Sciences in Uppsala, Sweden discuss the control of V. destructor in honey bee
colonies by management methods and organic and traditional methods of chemical control
A range of chemicals that occur naturally in the honey bee
colony environment and that are present in honey can
be used to control V. destructor. The most commonly
used so-called organic acaricides are formic, lactic and
oxalic acids. It is believed that the acaricidial effect is based
directly on a lowered pH which is less well tolerated by the
smaller mite than the larger bee. Thymol, a substance found
in high quantities in some types of honey, is also widely
used.
Formic acid has been the most commonly used organic
acid for varroa mite control. There are numerous ways of
applying formic acid to control varroa. An advantage with
formic acid is that there is also some miticidal effect on
mites in sealed brood (Fries, 1991). Disadvantages include
variation in efficacy and risks for the user handling concentrated
acid. Formic acid fumigation is best used in the
temperature range 12–25°C. Below this temperature the
efficacy is reduced and above this temperature the bees may
become agitated and leave the hive.
Lactic acid is applied in a 15% water solution sprayed
directly on each comb side covered with bees. The treatment
is very effective if repeated three times and well tolerated by
the bees (Brødsgaard et al., 1997). However, it is very labour
intensive.
Oxalic acid has more recently proved to be highly
effective for mite control, both applied dissolved in sugar
solution dripped onto the bees or as a fumigant applied
after heating oxalic acid crystals inside the bee hive
Oxalic acid is only effective in broodless
colonies and if applied in the late autumn problems with
increased residues in honey are minimal.