MICROBIAL DISEASES OF INSECTS 92 1 



end to end. Aerobic; shrinks perceptibly when treated with Gram's stain, almost 

 to half its size. Stained bacilli show unstained spots (spores). 



In plate cultures B. tracheltis develops into small circular colonies 0.25 to 0.75 

 mm. in diameter, which are covered with tubercles when the colony grows in gela- 

 tin. Gelatin colonies are finely granular of a deep brownish-yellow color, opaque 

 center surrounded by a transparent ring. Gelatin is liquefied in twenty-four to 

 forty-eight hours. Gelatin stab cultures are typical, having a cup-shaped hollow 

 funnel at the surface, a short empty stem; then the culture grows in the depth of 

 the gelatin, liquefying it in the shape of a carrot, later becoming the shape of an 

 inverted bottle; the culture is seen along the original path of the stab as a zigzag 

 line which later forms a compact cream-colored deposit as the gelatin becomes 

 entirely liquefied; these cultures have the odor of the white of an egg. Broth 

 cultures are clear the first twenty-four hours; after that they become turbid and 

 a pellicle forms which thickens with age, sediment compact; cultures become 

 wholly transparent in four to six months. 



METHODS OF INFECTION. Washing the larvae of the Lamellicornice 

 with the natural virus of graphitosis kills 16.6 per cent to 100 per cent 

 but an augmented virus gives 100 per cent mortality. The injection 

 under the skin of a very small drop of graphitosis blood is always fatal 

 for the larva even if the virus is weak. 



B. tracheitis multiplies first in the blood system, then fills the 

 Malpighian tubes, next characteristically in the trachea and then in the 

 fatty bodies; the trachea becomes typically filled with black amorphous 

 granules from whence the name of this organism; the fat cells are at- 

 tacked. The intima of the muscles, trachea and other organs is covered 

 with bacilli, which however do not penetrate the organs themselves. 



AMERICAN FOUL BROOD 



Bacillus larva White* 



HISTORY AND DISTRIBUTION. American foul brood is the prevalent 

 disease among bees in America and is distributed through all parts 

 of the United States, in Ontario, Canada, Switzerland, New Zealand, 

 Germany, England, and France and it is probable that it has a much 

 wider geographical distribution. 



SYMPTOMS. American foul brood or simply "foul brood" usually 

 shows itself in the larva just about the time that the larva fills the cell 

 and after it has ceased feeding and has begun pupation. 



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



* White, G. F. American foul brood. Bui. 809. Bur. of Ent. U. S. Dept. of Agr., 1920. 



