Here's a good data report:
A Review of Treatment Options for Control of Varroa Mite in New Zealand
PDF version (151 KB)
http://www.biosecurity.govt.nz/pests-diseases/animals/varroa/paper/varroa-treatment-options.htm
Trade Name(s): Apivar
Active Ingredient: Amitraz (500mg/strip)
Chemical Class: Amadine
Method of Application: Apivar consists of a plastic polymer embedded with amitraz, a contact miticide. The strips should be placed in the hive with one strip used for every 5 frames of bees in each brood chamber. The strip is hung between the frames, with the frames separated slightly so that both sides of the strip come into contact with the bees. The bees rub against the strips as they move through the brood chamber, and then pass the chemical on to other bees as they rub up against each other in the hive. The strips should be removed after 6 weeks.
Amitraz has also been used for varroa control in the past applied as a spray (Mitac), and as a fumigant impregnated on potassium nitrate soaked filter paper and ignited on the bottom board (Taktik).
Effectiveness: Amitraz was one of the earliest chemicals tested for varroa control, with studies dating back to 1979. Early studies are reviewed by Merrington106. More recently, amitraz in plastic strips has been shown to produce varroa mortality of 97-99%6. Amitraz sprayed once and twice killed 90 and 96% of mites respectively 93. Various concentrations of amitraz killed over 98% of mites, and fumigation strips killed over 99% of mites60.
Adverse Effects: A preparation of amitraz (Apivarol) was found to increase mortality of 1-3 day old larvae (61% vrs. 83% for control)4. A fumigation strip of amitraz caused some bees to leave their hive and form clusters98. Fumigation strips also caused high adult bee mortality in package bees60.
Operator Safety: Amitraz is classified by the EPA in the US as Class III – Slightly Toxic. There are unlikely to be operator safety issues for amitraz in the plastic strip form.
LD50: Rats – 523-800mg/kg (oral); >1600mg/kg (dermal)
Residues: Amitraz is a fat-soluble compound, but unlike other such compounds used as varroacides, it is volatile and unstable in honey, degrading in 3-4 weeks76. Amitraz has therefore not been found as a residue in honey95. Beeswax appears to accelerate the degradation of amitraz, with the product not being detectable within hours of application140. Amitraz was not detectable when added at 100ppm in beeswax foundation, although fluvalinate and coumaphos were present in levels similar to the amount added51.
MRL’s: Official maximum residue levels for amitraz in honey range from 0.01ppm in Italy, Germany and Switzerland to 1ppm in the US. The EU level is 0.2ppm140. No MRL has been established for amitraz in beeswax, since the substance has never been found as a residue in beeswax.
Resistance: Amitraz was found to be ineffective in killing mites in the former Yugoslavia, even though the product provided good mite control in the 4 previous years. The mites were believed to be resistant to amitraz34. Amitraz resistance was also confirmed in a population of mites in the US that showed resistance to fluvalinate38. Amitraz resistance has been shown in laboratory assays108
Cost: Between NZ$8.10 and NZ$14.95 per treatment, based on French prices (assuming 10 frames of brood, and therefore 2 strips per hive). According to the manufacturer, the low end price may be influenced by government subsidies.
Labour costs for Apivar are minimal, with two visits per hive 6 weeks apart. One or both visits could be incorporated into normal hive management. Estimated time necessary for application has been determined at 2 minutes per beehive per visit for strip products. Spray application would be 21 minutes per beehive. No figures are given for fumigant products50.
Impediments to Registration: While there is substantial data available on the use of amitraz as both a spray and fumigant, there appears to be far less on the efficacy of strips. Because of good dosage control, however, the strips are likely to provide better efficacy without side effects on bee behaviour and mortality. Apivar is registered for use in Portugal, Ireland, Italy, Belgium and France. There is therefore likely to be sufficient efficacy data available to meet registration requirements in New Zealand should the manufacturer or an importer choose to register the product.