Evaluation of honey bee miticides, including temporal and thermal effects on formic acid gel vapours, in the central south-eastern USA

Abstract

SUMMARYTwo field studies were conducted in the central south-eastern USA (Tennessee) to evaluate the efficacy of miticides for Varroa destructor and Acarapis woodi and treatments' effects on honey bee (Apis mellifera) colony health. We also determined the concentration of formic acid throughout the period that colonies were treated with formic acid applied to pressed fibre-board and in gel packs. In a late spring application, formic acid vapours dissipated more rapidly in gel-pack-treated colonies, dropping to an average of < 5 ppm at 13 d post-application. Average concentrations were 15 ppm at 13 d post-application in board-treated colonies. No deleterious effects on adult bee or brood populations were detected. However, formic acid fibreboard-treated colonies stored less honey during the treatment period. In a trial begun in late summer, gel packs, Apilife VAR (containing thymol, eucalyptus oil, menthol and camphor), Apistan (tau-fluvalinate) and oil strips (containing origanum and bay in olive oil) were evaluated. Comparisons of mite drop after a 42-d treatment period indicated Apilife VAR and formic acid gel packs provided control similar to that of Apistan. Oil strips were usually shredded and removed by bees and provided little control. Tracheal mite incidence was reduced 100%, 97% and 92% by formic acid gel packs, oil strips and Apilife VAR, respectively, whereas incidence increased by 75% in untreated colonies. Amounts of bees and brood were less in all treatment groups and in untreated controls. We believe this was a result of natural colony size reduction. Amounts of food stores were unchanged for all treatment groups except there was less honey found in oil-strip treated colonies after treatment. Formic acid vapours from gel packs dissipated less rapidly as ambient temperatures decreased. A regression equation predicted that, under early autumn climatic conditions, vapour concentrations would reach 10 ppm at 21 days after application.