Rotenone for Varroa destructor control: effectiveness in field trials

Two field trials were performed in an experimental apiary of Apis mellifera L. Langstroth hives in Miramar (Argentina) during spring (Sept.-Nov. 2001) and autumn/winter (Jun-Jul 2002), to evaluate the effectiveness of rotenone impregnated in polyvinyl chloride strips against Varroa destructor (Anderson & Trueman). Colonies were standardized for consistency of adult bee population, brood combs and food storage. In spring, a group of 10 colonies received 1.2 g of rotenone/hive (0.6 g/strip). Another group of 10 colonies received 0.8 g of rotenone/hive (0.4 g/strip). Five colonies were left untreated. In autumn/winter, a group of 10 colonies received 0.8 g of rotenone/hive, while 7 colonies were left untreated. During the assay, female adult mites collected at the bottom of each hive were counted three times per week. After twenty days, all strips were removed and fluvalinate and oxalic acid miticides were applied, to determine the mites remaining in each hive. Rotenone effectiveness was evaluated by the percent efficacy (E%) and the percent control (C%), according to Abbott’s formula. Efficacies of 79.2 and 82.7 per cent for the spring and autumn/winter treatments, respectively, were observed. Bee mortality ranged between 10 and 20 per cent. A single treatment of 0.8 g of rotenone/hive was enough to control Varroosis and represents a promising alternative for beekeepers.