BEES IN COLONIES AFFECTED BY EUEOPEAN FOULBROOD 27 



the source of larval food at various stages needs further substantia- 

 tion. 



6. Irrespective of strength of colony, the Italian bees were found 

 to resist infection much better than hybrids and showed more ability 

 to overcome the disease. 



7. This apparent resistance of the Italian bees was observed to 

 be largely due to the more vigorous house-cleaning characteristics 

 rather than to a natural resistance or immunity to the disease. 

 There was very little difference in the apparent period of incubation 

 between the Italian and hybrid colonies, possibly a slight difference 

 in favor of the Italians. Furthermore, it was noted that often there 

 may be a slight recurrence of disease in the brood of the new Italian 

 queen until a sufficient number of her bees have emerged to eliminate 

 the infection by house cleaning. Apparently, infection is not always 

 entirely removed by a period of queenlessness. 



8. As a rule, requeening is necessary in the treatment of European 

 foulbrood, except possibly in the strongest Italian colonies, which 

 show only slight infection. Where a considerable quantity of dis- 

 ease is present, sufficient to require treatment, it was found unsafe 

 to use a period of less than 10 days' queenlessness, due to the infec- 

 tious condition of the diseased material remaining and the accom- 

 panying behavior of the colony. 



9. The stronger the colony in Italian bees, the more rapid was the 

 recovery. 



10. A heavy honey flow tends to prevent infection from gaining 

 a foothold. It also tends to eliminate the disease if present before 

 the start of the heavy honey flow. This was found to be due to the 

 effect of dilution on the infection because of the influx and direct 

 feeding of the fresh nectar to the larvae. 



11. European foulbrood is a disease of weak colonies. It was 

 found to be difficult effectually to infect any but the very weak 

 colonies during the heavy honey flow. Therefore, colonies kept 

 strong up to the time of the honey flow run very little danger of 

 contracting European foulbrood. This and others of the facts ob- 

 served are in exact harmony with facts already observed in apiary 

 practice. 



