DIAGNOSING BEE DISEASES IN THE APIARY 17 



as a decayed larva is removed from the comb, and can also be 

 detected in the dry scales. 



A reliable symptom of this disease is a reddish-brown color and 

 ropy consistency of decayed brood, particularly when accompanied 

 by a pronounced putrid odor. 



Sacbrood 



Sacbrood is caused by a filterable virus, an organism so small that 

 it will pass through a porcelain filter and cannot be seen under the 

 most powerful microscope. Infection in the case of sacbrood takes 

 place by way of the alimentary canal. Both worker and drone brood 

 may be affected. It has not been definitely determined whether or not 

 queen larvae are killed. Pupae are killed occasionally, but adult bees 

 are not affected. 



IMPORTANCE 



Sacbrood is a widely distributed disease but it usually does not 

 cause serious losses. It is important, however, for beekeepers to recog- 

 nize sacbrood so that it will not be confused with the foulbrood 

 diseases. 



Sacbrood may appear at any time during the brood-rearing season, 

 but it is most common during the first half of the season, and prac- 

 tically always subsides after the main honey flow has started. In 

 ordinary cases the colonies are not noticeably weakened by sacbrood, 

 but in exceptional cases, when 50 percent or more of the brood is 

 affected, they may be considerably weakened. 



SYMPTOMS 



APPEARANCE OF THE COMBS 



In colonies with sacbrood the brood is slightly irregular. Scat- 

 tered here and there among the healthy brood are cells containing 

 dead brood. The cappings over dead brood are first punctured and 

 later removed by the bees. The holes vary in size, and occasionally 

 there is more than one. Sometimes the size and uniform shape of the 

 hole indicate that the cell has never been completely capped. Dead 

 larvae usually lie fully extended on the floor of the cell (fig. 7, B-F), 

 the dark-brown heads showing through the openings. When these 

 conditions are present the dead larvae should be studied carefully. 



AGE OF AFFECTED LARVAE 



Death from sacbrood almost always occurs after the cell is capped 

 and the larva has spun its cocoon and is motionless. At this stage 

 the larva is fully extended on the floor of the cell. In heavily infected 

 colonies a few coiled larvae may be killed. 



COLOR AND ODOR OF THE DEAD BROOD 



Shortly after death caused by sacbrood the larva changes from the 

 pearly white to a slightly yellowish color. This gradually becomes 

 darker, beginning with the head and front third of the larva, which 



