Establishing honey bee colonies (Apis mellifera) with a queen cell enables high efficacy of natural acaricides against Varroa mites (Varroa destructor)

It is critical to improve Integrated Pest Management tools against the parasitic mite Varroa destructor – the leading cause of Apis mellifera honey bee colony losses in the U.S. Nonchemical controls (physical, biological, and cultural) against Varroa are not sufficiently effective to be widely adopted, and natural acaricides (those based on naturally occurring compounds) cannot be used effectively in all environmental and colony conditions. This leaves beekeepers reliant on a highly effective synthetic acaricide: amitraz. To provide beekeepers an opportunity to rotate with natural non-amitraz acaricides, we investigated whether a widely used cultural control method – starting new colonies with queen cells (immature queens) – could enable natural chemical controls to match the efficacy of amitraz. We established 177 experimental colonies using queen cells (cultural control). Colonies either served as untreated controls or received one of several synthetic or natural acaricides (chemical control). We measured the Varroa infestation rate of adult bees at establishment, and then post-treatment 75 days later. When combined with cultural control, we found that natural acaricides (oxalic acid vapor, oxalic acid dribble, repeated oxalic acid dribble, and HopGuard 3®) had efficacies of 43%, 66%, 79%, and 83%, respectively, while the synthetic acaricide (amitraz-based positive control) had 83% efficacy against Varroa. Our results suggest that natural acaricides based on oxalic acid and hops acids can rival the efficacy of a synthetic acaricide when strategically applied after installing queen cells in new colonies. None of these treatments appeared to negatively impact queen establishment success or honey production.