RNAi can be effective for the control of <i>Varroa destructor</i> in honey bee colonies

RNA interference (RNAi) can be utilised as a next-generation and species-specific pest management approach. We conducted long-term field trials to test the efficacy of RNAi for controlling the apicultural pest Varroa destructor. Honey bee (Apis mellifera Linnaeus, 1758) colonies were provided with pouches of sucrose solution containing a dsRNA treatment, with the active ingredient named vadescana, that targets the Varroa calmodulin gene to inhibit mite reproduction. High (4 g/L) and low (2 g/L) vadescana treatments were used at two field sites in New Zealand, each containing 160 colonies, and were compared with synthetic miticide treatments. Twelve weeks after trial initiation, both vadescana doses reduced mite populations compared to the untreated control with densities comparable to the synthetic miticide treatment. However, at one site (site B) where initially colonies were larger and mite infestations higher, only the high dose vadescana treatment demonstrated Varroa control. By the trial’s conclusion at 44 wk, colonies treated with the high dose vadescana at the other site (site A) had mite numbers of 9.9 mites per 100 bees, similar to those treated with synthetic strips. A significantly greater proportion of colonies from the high dose vadescana treatment survived the winter (45.0%) relative to the control colonies that received no Varroa treatment (7.5%). The field site with larger colonies and higher initial mite loads did not observe the same duration of control for the vadescana treatment. These trials indicate vadescana can be effective for Varroa management, particularly in colonies with low initial mite abundance.