STUDIES ON EUROPEAN FOUL BROOD OF BEES

Abstract

SUMMARY“European foul brood” has been initiated in healthy nuclei by feeding either the young larvae directly or the bees naturally infected material. The disease thus produced varied from a mild transient infection to a serious form depending upon whether the inoculation had been made early or late in the brood‐rearing season. In one experiment in which a nucleus very strong in bees was employed no disease resulted.“European foul brood” has also been induced in healthy nuclei by suspending in them combs containing artificially infected larvae in which disease had been produced by feeding them pure cultures of Streptococcus apis or Bacillus alvei and then starving them under conditions favouring the growth of the bacteria. The susceptibility of nuclei to infection by this means seems to be governed by approximately the same conditions as pertain to inoculations made with material obtained from natural sources. The disease thus induced ultimately becomes a mixed bacterial infection of the brood.Attempts to cause disease by feeding the bees or larvae (without starving them) relatively large numbers of S. apis or B. alvei organisms have as yet proved unsuccessful. Whether this is due to the fact that these bacteria become attenuated with respect to virulence by culturing them on artificial media, or that decomposing brood acts as a vehicle and that the relative inoculum is greater by this method, remains to be determined.The failure to produce “European foul brood” by feeding sterile Pasteur‐Chamberland L 2 or L 3 filtrates prepared from naturally infected larvae to the bees or larvae of healthy nuclei, either with or without bacteria, may be taken as strong evidence in support of the view that a filterable virus is in no way implicated as an etiological agent in this type of disease. This conclusion is strengthened by the success which has attended the use of pure cultures of the bacteria associated with this disease employing the “starved larvae” technique described.The introduction of queen bees from nuclei affected with “European foul brood” into healthy queenless nuclei has not caused any transmission of the disease under the conditions of the experiments.Two species of S. apis Maassen have been isolated from affected larvae taken from several different cases of “European foul brood”; one of these hydrolyses both casein and gelatine, the other does not. In other respects these species appear to be identical.The etiology of so‐called “European foul brood” is discussed in detail, and it is suggested from the evidence submitted in this and other papers that it may not be a single disease with one well‐defined etiological agent, as is American foul brood, but is, perhaps, a non‐specific mixed bacterial infection of the brood of bees, especially of the brood of weak colonies. This conclusion must be regarded as temporary pending further investigation.My thanks are due to Mr D. M. T. Morland and to Mr A. Rolt, whose generous advice and assistance in connexion with the apiary work greatly facilitated the carrying out of the practical experiments.