Evaluation of the impact of Exomite Pro™ on Varroa mite (Varroa destructor) populations and honeybee (Apis mellifera) colonies: efficacy, side effects and residues

In this research, we examined the application of thymol-based powder, directly over the top of the brood frames in colonies with different population in a 2-year study. The efficacy against mites, the side effects on bees and the contamination of honey were studied comparably to thymol-based gel treatment. In one-store colonies, thymol-based powder treatment gave average efficacy 64.5 % and did not differ significantly from thymol-based gel treatment (65.4 %). The natural mortality in control colonies was 41.4 % and the corrected efficacy (E (T)) during 2 years was 39.4 and 40.9 %, respectively. In two-store bee colonies, the application of thymol-based powder on top of each hive body gave higher E (T) (45,4 %) than on top of the double body hive (40.4 %), without statistically significant differences. The average concentration of thymol residues in honey 24 days after the application was 368 and 1,119 mu g kg(-1) for the honey of colonies treated with thymol-based powder and thymol-base gel, respectively.