The transmission of European foulbrood (Melissococcus plutonius) to artificially reared honey bee larvae (Apis mellifera)

The transmission of European foulbrood (EFB) was investigated by feeding larvae raised in vitro with a diet containing Melissococcus plutonius that had been artificially cultured or extracted from diseased larvae. EFB did not develop in larvae fed 1.1 x 10(9) artificially cultured M. plutonius organisms/ml. However, the use of M. plutonius extracted from diseased material effectively transmitted EFB to larvae at a minimum concentration of 200 M. plutonius organisms/ml. The method used to raise and infect larvae in vitro had an associated larval survival of 81.2-100% (mean 91.9%). A strong correlation (r(2) = 0.96) was established between the mortality of larvae that died from EFB and the dose of M. plutonius organisms. A clear linear relationship exists between the time duration of feeding M. plutonius inoculated basic larval diet (2 x 10(5) organisms/ml) and larval mortality (r(2) = 0.92).