Disinfection of Nosema ceranae-contaminated comb by irradiation, acetic acid fumigation and heat

Our goal was to evaluate methods for disinfecting Nosema ceranae-contaminated combs. One hundred ninety two frames containing honey combs were sprayed with an aqueous suspension of N. ceranae, so that each colony received a dose of 4.5 × 10⁸ spores. Inoculated brood chambers were allocated to five groups(n=12): 1. Irradiation (10 kGy electron beam radiation). 2. Acetic acid fumigation (480 mL of 80% (v/v) acetic acid). 3. Heat (24 h at 49 ± 0.1°C). 4. Inoculated (no disinfection). 5. Non-inoculated (neither inoculated nor disinfected). Bulk bees (1 Kg) were established in each brood chamber in May 2009 and monitored for 18 months. Colonies were evaluated for infection level, colony population and honey production. Our data suggest that only irradiated brood chambers maintained the same low level of infection as non-inoculated brood chambers throughout the study. In contrast, within a month after establishment, inoculated untreated brood chambers had significantly higher infection, whereas, acetic acid fumigated and heat treated chambers were intermediate. While colony population did not differ among treatments in 2009, by June 2010 inoculated untreated colonies had the fewest adult bees and sealed brood compared to the other treatments. Honey production did not vary significantly among treatments in 2009 and results from 2010 are pending. We conclude that irradiation is the most effective method of disinfecting N. ceranae contaminated combs. In addition, the phenology of infection appears similar to that of N. apis, with infection levels declining in mid-summer following a spring peak.