MICROBIOLOGY OF DISEASES OF INSECTS 647 



At this time it is sealed over in the comb. The first indication of 

 the infection is a slight brownish discoloration and the loss of the well- 

 rounded appearance of the normal larva. At this stage the disease is 

 not usually recognized by the beekeeper. The larva gradually sinks 

 down in the cell and becomes darker in color, and the posterior end lies 

 against the bottom of the cell. Frequently the segmentation of the 

 larva is clearly marked. By the time it has partially dried down and 

 become quite dark brown (coffee colored) the most tj^ical character- 

 istic of this disease manifests itself. If a match stick or tooth-pick is 

 inserted into' the decaying mass and withdrawn the larval remains ad- 

 here to it and are drawn out into a thread, which sometimes extends for 

 several inches before breaking. 



This ropiness is the chief characteristic used by the beekeeper in 

 diagnosing this disease. The larva continues to dry down and gradually 

 loses its ropiness until it finally becomes a mere scale on the lower side 

 wall and base of the cell. 



The scale formed by the dried-down larvae adheres tightly to the 

 cell and can be removed with difficulty from the cell wall. The scales 

 can best be observed when the comb is held with the top inclined to- 

 ward the observer so that a bright light strikes the lower side wall. A 

 very characteristic and usually penetrating odor is often noticeable in 

 the decaying larvae. This can perhaps best be Ukened to the odor of 

 heated glue. 



The majority of the larvae which die of this disease are attacked 

 after being sealed in the cells. The cappings are often entirely removed 

 by the bees, but when they are left they usually become sunken and 

 frequently perforated. As the healthy brood emerges the comb shows 

 the scattered sunken cappings covering dead larvae, giving it a char- 

 acteristic appearance. 



Pupae also may die of this disease, in which case they too, dry down, 

 become ropy, and have the characteristic odor and color. The 

 tongue frequently adheres to the upper side wall and often remains there 

 even after the pupa has dried down to a scale. Younger unsealed larvae 

 are sometimes affected. Usually the disease attacks only worker 

 broqds, but occasional cases are found in which queen and drone broods 

 are diseased. It is not certain that race of bees, season, or climate 

 have any effect on the virulence of this disease, except that in warmer 



