Large-Scale Fumigation with Ethylene Oxide of Honeybee Combs Contaminated with Bacillus Larvae

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Abstract
Summary Brood combs contaminated with American foul brood (AFB) were fumigated with ethylene oxide (ETO) in a large heated vacuum chamber. ETO concentrations up to 435 mg/litre applied as Oxyfume 12, at temperatures as high as 54°C, did not sterilize B. larvae spores in the residues of larvae killed by AFB. Spore suspensions of an indicator organism, Bacillus subtilis, were not regularly killed by the treatments, although chemical indicator cards used in monitoring the fumigation process indicated complete sterilization. Fumigation in a small chamber at 35°C, nearly 100% RH and with an ETO concentration 450 mg/litre sterilized B. subtilis after 16 h, and B. larvae after 24 h. Indicator cards became a deep green by 24 h, showing a sufficient exposure to ETO. AFB infection in package bee colonies hived on treated combs was variable. Half the treated colonies developed fresh infection during the season and were then treated with Oxytetracycline to control the disease.