266 



AMERICAN BEE JOURNAL 



August 



Some Observations on European Foulbrood 



By G. F. White, Bureau of Entomology, U S. Dept. Agr., Washington, D. C. 



(ConcUulcd from July) 

 Length of Time the Germ Lives 



The germ Bacillus pluton grows and 

 multiplies probably only in the stom- 

 ach of infected bee larvae, and very lit- 

 tle, if any, after the larva dies. 

 Sooner or later, however, it dies if it 

 is not fed again to healthy larvse. 

 Many experiments were made relative 

 to the amount of heat, dryitig, sun 

 light, fermentation, putrefaction and 

 carbolic acid the germ will withstand. 

 The periods it will live in honey, pollen, 

 and in decaying larv;e were also sub- 

 jects for study. In performing the ex- 

 periments, disease material containing 

 the germ was subjected to these vari- 

 ous environments, respectively, and 

 then was fed to healthy brood to de- 

 termine when the germs were de- 

 stroyed. 



The approximate period the germ of 

 European foulbrood will remain alive 

 in various environments may be esti- 

 mated from the following results: 



When the germ was placed in water 

 and heated for 10 minutes it required 

 146 degrees F. to destroy it. 



When it was heated in honey for 10 

 minutes it required 175 degrees F. to 

 destroy it. 



The stomach contents of diseased 

 larva: were smeared on glass slides 

 and allowed to dry. When these were 

 shielded from the light the germ 

 lived about a year. 



When siinilar smears were exposed 

 to the rays of the sun the germ was 

 destroyed in about 3 hours. 



When placed in water it was de- 

 stroyed by the sun in about 6 hours. 



When in honey the sun destroyed it 

 in about 4 hours. 



It was destroyed in a 10 per cent 

 sugar solution fermenting at room 

 temperature within 3 weeks. 



It was still alive after one month in 



a 20 per cent honey solution ferment- 

 ing at outdoor temperature. 



In a putrefying solution at room 

 temperature it was destroyed in 

 about 35 days. 



In a similar solution at outdoor 

 temperature it was still alive after 40 

 days. The time required to destroy 

 it was not determined. 



Placed in honey and kept at room 

 temperature the germ died in from 3 

 to 7 months. 



Mixed with pollen, the germ lived 

 for more than / months at room tem- 

 perature. The maximum period has 

 not been determined. 



The germ lives for a number of 

 days in a half per cent aqueous solu- 

 tion of carbolic acid, but is killed 

 rather quickly by strengths ordi- 

 narily used as a disinfectant. 



Other things being equal, the germs 

 live longer in a cool environment 

 than in a warm one. 



It will be observed from these facts 

 that the germ of European foulbrood 

 lives only about a year under quite 

 favorable environment; that it is 

 readily destroyed by a number of 

 factors in nature, and by heat and 

 disinfectants. 



Spread of European Foulbrood 



The discussion of the transmission 

 of any bee disease may be consid- 

 ered under three subdvisions — the 

 spread (1) from diseased larvae to 

 healthy ones within the same colony. 

 (2)from a diseased colony to a heal- 

 thy one within the same apiary and 

 (3) from a diseased apiary to a 

 healthy one. 



Naturally the germ Bacillus pluton 

 must be present in a colony or there 

 can be no European foulbrood in it. 

 The spread of the disease, therefore, 

 involves directly the spread of the 

 germ that causes it. The infected 

 larva is the source for the multiplica- 



Fig. 7. Experimental apiary for study of bee discasea 



Fig. 6. Hive for exp^ri.ii^.Kal colony 



tion of the germ and the adult bees 

 have a tendency to remove these lar- 

 vae pieceiTieal, thus removing the 

 germs. If the disease material is fed 

 to healthy larvae before the germ 

 dies, the disease will be transmitted; 

 if, on the other hand, it does not 

 reach the stomach of such larvae be- 

 fore the germ dies, naturally the dis- 

 ease will not be spread. These facts 

 form a good starting point in a con- 

 sideration of the problem of the 

 spread of the disease. 



Were it possible to trace complete- 

 ly the course of the fragments of lar- 

 vae removed, until the disease-produc- 

 ing germ Bacillus pluton which the)' 

 contain was dead, one could describe 

 in considerable detail the mode of 

 transmission of the disease. While 

 to do this is well nigh impossible, 

 much has been done in a more indi- 

 rect way toward the solution of the 

 problem. 



As a result of the removal of the 

 sick and dead larvae by the adult 

 bees, European foulbrood colonies 

 were found to manifest a marked 

 tendency to recover from the dis- 

 ease. The fragments of larvae re- 

 moved are not fed, as a rule, there- 

 fore, directly to the brood. Were 

 they stored with the honey, so they 

 would not reach the young feeding 

 brood for a few months, no disease 

 would result, since the germ dies 

 comparatively soon when it is in 

 honey. 



Inasmuch as Bacillus pluton may 

 remain alive for a considerable pe- 

 riod in the scales, it seems quite prob- 

 able that through them the disease 

 might be carried over a period of 

 months and possibly, at times, over 

 winter. The pollen in European foul- 

 brood colonies might possibly also be 

 a source of infection for a considera- 

 ble period. 



Once carried out of the hive and 

 released from the bees, the germs en- 

 counter various agents which tend to 

 destroy them, as drying, sunlight and 

 fermentation. The chance that such 

 germs while alive will be taken up by 

 adult bees and fed to healthy brood. 



