This Short Report contains key points from the report A beekeepers’ guide to understanding control measures for European Foulbrood (RIRDC Publication No 04/091 by Russell Goodman (Primary Industries Research Victoria, Knoxfield), Ben McKee (formerly PhD candidate, The University of Melbourne) and Peter Kaczynski (Department of Primary Industries, Ararat).

Researcher Contact Details Russell Goodman Primary Industries Research Victoria Private Bag 15 Ferntree Gully Delivery Centre, Vic, 3156 Phone: 03 9210 9222 Fax: 03 9800 3521 Email: russell.goodman@dpi.vic.gov.au

The presence of healthy honey bee larvae is essential for the well being of a honey bee colony. When larvae become sick and fail to develop into adult bees, the vitality and productivity of a colony declines.

European foulbrood (EFB) is an economically important honey bee brood disease that effects colonies throughout much of the beekeeping areas of Australia. Infected colonies may become poor honey producers and unsuitable for crop pollination. Understanding this disease and its control is essential for successful beekeeping.

EFB (Melissococcus pluton) is controlled by specific apiary management practices and when necessary by application of the antibiotic, oxytetracycline hydrochloride (OTC).

A major aim of the research was to investigate OTC residues in honey. Six groups of colonies were treated with a 1 g active dose of one of three OTC products in either sugar syrup or caster sugar. Honey was extracted 43 days later from the supers of the six hives of each treatment group which was then sampled and analysed. Residues were found in all samples from the six treatment groups, but not in any honey of a second later extraction.

Higher residues were present in sugar syrup treatments (mean 0.34 mg/kg) than in caster sugar treatments (mean 0.065 mg/kg).

Degradation of OTC in honey was investigated by storing honey of the six treatment groups of the first extraction at 22ºC and ambient temperature. Residues were detected in all ambient temperature honeys sampled exactly twelve months from the date of application. OTC degraded at a faster rate in the same six lines of honey stored at 22ºC.

The research found that 0.5 g and 1.0 g of OTC in caster sugar and 0.5 g OTC in 200 mL of distilled water delivered sufficient antibiotic to honey bee larvae in two-storey colonies to exceed the 1-2 µg/mL minimum inhibitory concentration of OTC for M. pluton.

The mean concentration of OTC in larvae was significantly greater for a 1.0 g dose than for a 0.5 g dose in caster sugar administered to twostorey colonies. Further laboratory and field work is necessary because these results were obtained by assay of whole larvae rather than assay of the larval gut, the site where M. pluton multiplies.

During 2000 and 2001, commercially managed honey bee colonies were fed either 1.0 g OTC, protein dietary supplement or left as untreated controls to determine their effect on the incidence of EFB. The application of OTC resulted in total protection against EFB for these colonies in 2000 and for 12 of 13 treated colonies in 2001. In 2001, the mean incidence of EFB in colonies fed protein supplement was 9% lower than the controls, but this result was not statistically significant. There was no significant statistical difference in spring honey production or in the mean level of crude protein of adult bees sampled from the 3 treatments at the completion of the trial in 2001. There was a significant statistical relationship between the number of days with rain per month and incidence of EFB in colonies fed supplement.

Honey bee larvae, about 4-5 days old, were sampled from five commercial apiaries in central and western Victoria. The mean pH varied significantly between apiary locations (range 6.258 to 6.506) and was probably a result of bees foraging on different plants. The pH of larval guts was similar (6.277 and 6.258) at two sites with the same plant species even though the sites were approximately 100 km apart.

Laboratory studies indicated that larvae have a capacity to buffer their diet and consequently may not be adversely affected by changes in pH of larval food as suggested by other reports.

An existing hemi-nested polymerase chain reaction (PCR) assay was modified to obtain increased sensitivity for the detection of M. pluton. The modified PCR confirmed M. pluton in larvae, individual body components of adult bees, pollen, brood comb cells that contained a freshly laid egg, and broodnest honey, all sampled from infected colonies. M. pluton was also found in larvae, adult bee digestive tracts and broodnest honey of healthy colonies, even though disease signs were not evident in the brood.

Honey bee larvae were successfully reared and inoculated with suspensions of M. pluton in the laboratory. These procedures will enable fast, controlled laboratory studies to be conducted on the effect of nutrition and other potential treatments for the control of EFB. They will replace costly field and cage trials and enable trials to avoid variable factors such as pollen and nectar resources and weather.

A survey of apiarists conducted in 1999 found that 62% of Victorian respondents treated colonies with OTC only when EFB symptoms were present in the brood. Forty-nine percent of respondents chose to spot treat only infected colonies rather than blanket treat all colonies in an apiary. The survey indicated that good nectar and pollen flows were important for the reduction or prevention of EFB. In contrast, feeding protein supplement to improve honey bee nutrition was considered not beneficial. Locating colonies on sunny, warm, sheltered sites plus regular requeening and replacement of broodnest combs assisted control of the disease.

For further information on this project refer to the full technical report, which is published on the the RIRDC website (http://www.rirdc.gov.au/reports/HBE/ w04-092.pdf ) or the abridged version for beekepers (RIRDC Publication No 04/091), available from RIRDC. Or contact the principal researcher.


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