| The varroa mite, Varroa destructor Anderson and Trueman, is a threat to the beekeeping industry. Using formic acid indoors in winter is one method for controlling this ectoparasite in honey bee, Apis mellifera L., colonies. This study consists of experiments conducted to determine the most efficacious treatment regime that also minimizes harm to honey bees.;The prevalence of tracheal mites was not affected by formic acid fumigation, however, tracheal mite mortality was significantly increased by formic acid fumigation. Nosema spore mean abundance was significantly suppressed by formic acid fumigation in only one of four experiments. However, in all experiments, nosema spore abundance was lower in treated than in untreated colonies.;During fumigation, the concentration of formic acid in hive air was consistently lower than that in room air possibly because honey absorbs the acid. Workers fed acid-laden sugar syrup in summer were less attentive to queens when fed 100 ppm formic acid, than when fed 0 or 1000 ppm formic. The quantity of each component of the queen's pheromone blend was not affected by formic acid treatment. However, one component, methyl p-hydroxybenzoate, varied with season.;Varroa mite mortality was significantly increased by formic acid fumigation, in a concentration-dependent manner. Long-term low concentration fumigation and short-term high concentration fumigation both provided good efficacy. Worker bee mortality was not increased by fumigation, but high concentration fumigation caused significant queen loss. Long-term low concentration fumigation or high concentration fumigation with step-wise temperature-dependent room ventilation prevented queen loss. There was no effect of treatment on any measure of performance of surviving queens during the summer following treatment. |
