SAGBKOOD. 25 



In the quotation Dadant expresses the belief that the disease is an 

 infectious one. This view has been proved by recent studies to be the 

 correct one. Since the disease is one of a somewhat transient nature, 

 .often subsiding and disappearing quickly without treatment, and is 

 quite different in many ways from the f oulbroods, it is not strange that 

 some writers should have held that it is not infectious. 



PREDISPOSING CAUSES. 



Beekeepers have known for many years certain facts concerning the 

 predisposing causes of sacbrood. Recent studies have added others 

 relative to sex, age, race, climatic conditions, season, and food as 

 possible predisposing factors in the causation of the disease. 



Age. — The results of the studies suggest that adult bees are not 

 directly susceptible to the disease. Pupse are rarely affected (PI. 

 II, zz). If one succumbs to the disease, it is quite soon after trans- 

 formation from the larval stage. Primarily it is the larvae that are 

 susceptible. When a larva dies of the disease, it does so almost 

 invariably after capping, and usually during the 2-day period immedi- 

 ately preceding the time for the change to a pupa. 



Sex. — Worker and drone larvse may become infected. Queen larvte 

 apparently are also susceptible, although this point has not yet been 

 completely demonstrated. 



Race. — No complete immunity against sacbrood has yet been found 

 to exist in any race of bees commonly kept in America. That one 

 race is less susceptible to the disease than another may be said 

 to be probable, although the extent of such immunity has not been 

 established. 



The question: "What race of bees is there in the diseased colony? " 

 was asked beekeepers sending samples of diseased brood. Out of 140 

 rephes received from those sending sacbrood samples, 53 reported 

 hybrids, 49 reported Itahans, 21 reported blacks, and 17 reported 

 Itahan hybrids. These replies show that the bees commonly kept by 

 American beekeepers are susceptible, although their relative suscepti- 

 bihty is not shown. 



The bees which have been inoculated in the experimental work 

 on sacbrood have been largely Italians or mixed with Itahan blood. 

 Blacks have also been used. No complete immunity was observed 

 in any colony inoculated. That the blacks are more susceptible 

 than strains having Italian blood in them is suggested by some of the 

 results. Facts concerning the problem of immunity as relating to 

 bees are yet altogether too meager to justify more definite state- 

 ments. 



Climate. — Historial evidence strongly suggests that sacbrood is 

 found in Germany (Langstroth, 1857), England (Simmins, 1887), 

 58574°— Bull. 431—17 i 



