Effects of delayed acaricide treatment in honey bee colonies parasitized byVarroa jacobsoniand a late-season treatment threshold for the south-eastern USA

Abstract

We set up 72 colonies of honey bees (Apis mellifera) in the piedmont region of Georgia and South Carolina, USA (2 states × 6 apiaries per state × 6 colonies per apiary) in April 1995. Colonies were individually housed in single-chamber Langstroth hive bodies and one honey super, started with standard mail-order 0.9 kg (2lb) packages of bees containing small incipient populations of the parasitic mite Varroa jacobsoni, and managed optimally as for honey production. Within each state, each apiary was assigned one of the following treatments: (1) treatment with Apistan acaricide in June, (2) treatment in August, (3) treatment in October, or (4) no treatment By December, colony bee populations were optimum in August-treated apiaries. Month of treatment did not affect bee body weight. There were treatment by state interactions for number of sealed brood cells, colony mite populations, and percentage of brood cells with disease-like symptoms. Our data suggest that late-season acaricide treatments in first-year colonies in the south-eastern USA piedmont are justified at colony mite populations of 3172 ± 324, 300-bee ether roll mite levels of 15 ± 1.4, and overnight adhesive bottom board insert mite levels of 117 ± 15 in colonies with 24 808 ± 2245 bees and 1825 ± 327 cm² sealed brood; these conditions occurred in mid-August Acaricide treatments in or before August may eliminate mite-associated brood pathology in the south-eastern USA. Bottom board inserts were more reliable predictors of colony mite populations compared to the ether roll method.