Abstract
Efficacies of two miticides, Apivar® and Thymovar®, were evaluated as a fall treatment against V. destructor. The effect of treatment with miticides was further evaluated by monitoring both viral load and rate of indoor overwintering survival of colonies of European honey bees (Apis mellifera L.) in the vicinity of Saskatoon, Saskatchewan, Canada. Forty-five colonies were randomly assigned to three treatment groups with 15 hives per group: Group 1; 2 strips of Thymovar® (thymol); Group 2; 2 strips of Apivar® (Amitraz); and Group 3; no treatment (control). Significant decreases in the rates of colony infestation (Mites per hundred bees, MPHB) by V. destructor were observed (p < 0.05) between colonies of bees treated with Apivar® in October 2013 when compared to control colonies. Efficacy of Apivar® and Thymovar® against V. destructor after treatment for 22 days were 76.5 and 26.7%, respectively. After 22 days, concentrations of the two miticides in bees were 15.4 ng amitraz/g wet mass (wm) and 64,800 ng thymol/g wm. There were no significant differences (p > 0.05) in the percentage of colonies infected by deformed wing virus (DWV) and Israeli acute paralysis virus (IAPV) either before or after treatment with Apivar® or Thymovar® in October 2013 and 7 months post treatment in April 2014. Only the Apivar® treatment group showed IAPV infections in April 2014. The group treated with Apivar® exhibited a better overwintering rate of survival (93%), than hives treated with Thymovar® (67%). These results suggest volatile miticides like Thymovar® should be avoided in geographical areas with colder fall temperatures.
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