ABRC2010 Disinfection of Nosema ceranae Infected Comb by Irradiation Acetic Acid and Heat

The following was presented at the 2010 American Bee Research Conference in Orlando, FL.

24. Pernal, S.F., A. Ibrahim & A.P. Melathopoulos – DISINFECTION OF NOSEMA CERANAE-CONTAMINATED COMB BY IRRADIATION, ACETIC ACID FUMIGATION AND HEATNosema ceranae is an endoparasite first described from Apis cerana (Fries et al., 2006 Eur. J. Protistol. 32:356-365) that has subsequently spread to populations of Apis mellifera in Europe and throughout the world (Higes et al., 2006 J. Invertebr. Pathol. 92:93-95; Klee et al., 2007 J. Invertebr. Pathol. 96:1-10). In North America, the parasite has been associated with Colony Collapse Disorder in the U.S. (van Engelsdorp et al., 2009 PLoS ONE 4(8):e6481) and implicated in heavy wintering losses in Canada (Currie et al., 2010 J. Apic. Res. 49:104-106).

Though mechanisms of transmission for N. ceranae are not well understood, we hypothesized that decontamination of comb could be an important non-chemotherapeutic technique for managing this organism. We undertook an examination of new techniques of comb sterilization in addition to those previously demonstrated to be effective at suppressing Nosema apis (Bailey, l957 Am. Bee J. 97:24-26; Cantwell & Shimanuki, 1969 Am. Bee. J. 109:52-54).

Frames containing honey comb were sprayed with an aqueous suspension of N. ceranae, so that each colony received a dose of 4.51 × 108 spores. Inoculated brood chambers were allocated to four groups, each with 12 replicates, receiving one the following treatments: 1. Irradiation – 10 kGy of 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. A fifth, non-inoculated, treatment consisted of brood chambers receiving neither inoculation nor disinfection. Sixty 1-kg New Zealand packages were hived in the brood chambers on 2 May 2009. Colonies were sampled for N. ceranae spores by collecting a minimum of 30 adult bees on a weekly basis from 2 May to 4 June 09, after which time sampling occurred biweekly, then monthly during winter. Colony growth was evaluated by measuring adult worker population and sealed brood on 30 July and 30 August; honey production was weighed.

Thirteen days after hiving packages, spore levels within inoculated, untreated colonies rapidly proliferated to 2.4 ± 0.4 x 106 spores per bee while spore levels in irradiation, acetic acid fumigation and heat treatments remained below 167,000 spores. Nonetheless, by 21 May the acetic acid fumigation and heat treatments appeared less effective at suppressing spores than the irradiation treatment which remained similar to non-inoculated colonies. Separation among treatments diminished until 16 July when spore levels among all treatments, including those untreated, remained below 100,000 spores per bee. Considerable variability and increases in spore levels for the acetic acid fumigation and heat treatments were observed during the fall and early winter months.

Significantly more adult bees (F=4.52; df=4,52; P=0.0033) were found on the 3 July assessment in the irradiation versus heat treatment, with the fumigation, non-inoculated and inoculated treatments being intermediate in number. No significant differences among treatments were found for the area of sealed brood on this date, or for both parameters on 30 August. Honey production did not vary significantly among treatments.

In general, the acetic acid fumigation, heat and irradiation treatments all showed some suppression of the spring peak of N. ceranae spore development in bees, though suppression was more immediate and complete for irradiated comb. Only the irradiated treatment maintained spores at levels similar to non-inoculated colonies during the entire study.

More presentations from this conference can be found at Proceedings of the American Bee Research Conference 2010