Evaluating the new product Norroa™ against Varroa destructor in managed honey bee (Apis mellifera) colonies

Introduction Globally, beekeepers must manage the invasive mite pest Varroa destructor . The mite’s populations can grow quickly, overwhelming honey bee colonies through direct parasitism and the transmission of honey bee viruses. RNA interference is promising next-generation tool and has been demonstrated to control invertebrate pest populations. The novel product Norroa™ is the first of its kind marketed to beekeepers for the control of V. destructor . Field-level studies are critical to understanding the efficacy of the product and how to fit it into integrated pest management plans. Methods Field studies were conducted to test the effectiveness of Norroa™ during a nectar-flow season and a nectar-dearth season in Florida. In each field trial, 36 colonies were established for testing. Mite infestation rates were measured throughout the trials and mites were assessed for gene knockdown by determining RNA concentrations from the target gene. A final trial was conducted uncapping honey bee pupae and examining mite reproduction. Results During the nectar dearth, mite numbers started higher (4.56 mites/100 bees) and increased more in control colonies compared with the treated colonies, but differences were not significant. During the nectar-flow, Norroa™ maintained V. destructor populations at or below the initial infestation rate (2.31 mites/100 bees) for twelve weeks, compared with the control group that grew significantly higher than treated colonies. Mites from colonies that had been treated with Norroa™ were significantly less likely to lay an egg, or have any offspring emerge from the eggs laid. Discussion Research related to biological methods of control are currently under-studied relative to chemical treatments. These trials demonstrate the promise of a new tool for beekeepers to control V. destructor as part of a sustainable IPM approach.