Disinfecting honeycomb with ozone

US Department of Agriculture (USDA) research has shown that fumigating honeycombs with ozone gas can reduce pests, pathogens and pesticide levels. The two-part study was led by Rosalind James, an entomologist in the Agricultural Research Service’s (ARS) Pollinating Insect - Biology, Management, and Systematics Research Unit.

Pathogens such as chalkbrood fungus and the American foulbrood bacterium can persist for years on beekeeping equipment and in hives as dormant spores. They germinate when conditions are optimal and they attack the colony’s most vulnerable members - the larvae. Furthermore, the waxworms of the greater wax moth feed on the honeycomb.

Worker bees remove the mummified remains of larvae infected by the chalkbrood fungus. Photo by Stephen Ausmus.

Methyl oxide and gamma irradiation are among treatments that have proven effective for disinfecting honeycomb, but these treatments can be costly and impractical. James noted that fumigation with ozone - a highly reactive state of oxygen - can be easily set up by beekeepers on their own.

The first part of the study, published in 2011 in the Journal of Economic Entomology, demonstrated that fumigating combs with ozone at concentrations of 215 to 430 parts per million (ppm) killed all life stages of the greater wax moth, depending on length of exposure. Ozone also destroyed spores of the chalkbrood fungus after 24 to 36 h using 1500 ppm, while the American foulbrood bacterium required longer exposure times, high humidity levels and an ozone concentration twice as high.

Interior view of the ozone generator that supplies ozone to the fumigation chambers used in the studies. Photo by Rosalind James.

Honeybees are also exposed to pesticides while visiting flowers that have been sprayed or when they are treated for parasitic mites, said James. In January 2013, the team published results from the second part of their study in the journal Agricultural Science, this time detailing ozone’s breakdown of coumaphos, fluvalinate and several other pesticides that can accumulate in hives.

In experiments with glass vials containing residues of the pesticides, ozone exposures of 500 ppm for 10 to 20 h degraded 93 to 100% of coumaphos and 75 to 98% of fluvalinate. The ozone treatment also reduced or eliminated eight other common agricultural pesticides. Higher ozone concentrations and longer exposure times were required to reduce pesticide concentrations in wax and honeycomb samples.

The treatments also degraded the pesticides better in new honeycombs (less than three years old) than in older ones (more than 10 years old). James noted, “There’s something about the wax that can impede this breakdown, especially in a comb that’s been re-used in hives for many years. It may be that organic materials build up inside the wax, and these materials adsorb or break down the ozone before it can react with the pesticides.”

Beekeepers may be reluctant to discard honeycombs - even those which have become discoloured from years of use - because of the considerable effort bees put into making them. Ozone offers a solution for decontaminating honeycombs before re-use and can be carried out by beekeepers using commercially available equipment.

Credit: USDA/ARS