D3016: Concurrent treatment with two miticides for management of a honey bee parasitic mite: Effects on Varroa destructor and on Apis mellifera colonies

More than 30 years after the arrival of the ectoparasitic mite Varroa destructor, American beekeepers still struggle to manage this damaging pest of honey bees (Apis mellifera). While it is preferable to maintain low V. destructor levels throughout the year, rapid control is important if infestations reach a damaging level prior to the critical winter season. During the fall in Alabama, 32 colonies with high levels of V. destructor (mean infestation of adult bees 11.3%) were used to test if concurrent treatment with two registered active ingredients (amitraz and thymol) could improve the management of V. destructor compared to an amitraz treatment only. In late September, colonies were allocated to two treatment groups that received: 1) Four Apivar® strips (amitraz 3.3%) per colony; and 2) Four Apivar® strips plus 51 mL of Apiguard® gel (thymol 25%), all applied at one visit. Full colony assessments were performed before treatment application, mid-treatment (21 days post-application), and upon completion of the 42-day treatment period. This included visual estimation of the number of adult bees and the area of sealed worker brood (developing bees) per colony. At these points, V. destructor abundance on adult bees and percent brood infestation were also assessed, which allowed an estimate of the total V. destructor population per colony. Data analysis is ongoing to determine the effect of treatments on Apis mellifera colonies and on V. destructor. Colony survival until spring and the strength of colonies in spring will also be discussed.