Synergistic and molecular interactions between the formamidine amitraz and copper(II) sulfate,used against the mite Varroa jacobsoni O., a parasite of the honeybee Apis mellifera L.

Toxicological field assays have shown that the shock-treatment efficacy of the formamidine pesticide amitraz, used against the parasitic mite Varroa jacobsoni, is synergistically improved by the administration of copper(II) sulfate through feeding of the honeybees. Amitraz is autoxidized and this process is accompanied by chemiluminescence. The emission is enhanced in the presence of low concentrations of H₂O₂. A dose-related inhibition of the chemiluminescence by CuSO₄ was observed; consistent with the formation of copper-amitraz complexes evidenced in vitro. The results suggest the possibility that a protection of amitraz by cupric ions might be at the origin of the enhancement of its toxicity and thus makes a contribution to the observed synergy.