Q20 MICROBIAL DISEASES OF INSECTS 



GRAPHITOSIS* 

 Bacillus tracheitis or graphitosis Krassilstschik 



HISTORY AND DISTRIBUTION. This disease together with a bac- 

 terial septicemia was noted among the Lamellicornia in 1893 in the 

 southeast of Russia by Krassilstschik. He states that the larvae from 

 the Lamellicornia which formerly died en masse of muscardine,f die 

 of this disease very seldom in recent years. Bacterial parasites seem 

 to have replaced it in this part of Russia, and this is distinctly advan- 

 tageous since the bacterial diseases are much more destructive than 

 any of the species of muscardine. 



SYMPTOMS. At first the larva is entirely pure white, then several 

 legs change to a bright yellow color, next to a yellow brown. Little 

 by little this coloration extends over all the legs. Later on both sides 

 of the larva, characteristically in the region of the spiracles and around 

 them, the skin takes on a grayish hue which gradually deepens. The 

 larva is generally living at this stage but appears to be diseased. This 

 grayish coloration extends toward the back, and the anterior part of 

 the larva then gradually becomes gray also. At this stage the larva 

 is generally dead. After death, -the gray color, spreading characteris- 

 tically from the spiracles, deepens considerably, extending all over the 

 skin, finally acquiring a tint resembling that of polished graphite, 

 whence its name "graphitosis." This coloration is very characteristic 

 for the larva which die of this disease; it is only very rarely that the 

 cadaver is of a brownish shade. 



When the infection first shows in the legs, the movements are not 

 inhibited in any way, but when the graying around the spiracles sets 

 in, the larva becomes comatose yet still responding to exterior excita- 

 tions. It soon dies, retaining its characteristic curve but gradually 

 becoming limp and soft and decreasing in size, length, etc. 



CAUSAL ORGANISM. The bacillus of graphitosis is from 2/t to 2.2/z long having a 

 diameter of more than half its length; spores are produced; very motile, movements 

 quick and rapid; occurs generally in pairs from 3.6/1 to 4.6/4 long; long filaments not 

 produced; the longest do not exceed 7/1 to 9/1 which corresponds to two pairs of bacilli 



*Bacillary Diseases of Lamellicornia. In 1893 Krassilstschik described two bacterial 

 diseases attacking the larvae of the following insects: Rhizolrogus solstilialis, Melolonlha 

 vulgaris, Anisoplia austriaca, crucifera, and fruticola, Cetonia sp. and a larva belonging to 

 the Geotrupini (Lethrusf sp.). 



t Krassilstschik, I. Graphitosis and Septicemia of Insects. Memoires Soc. Zool. en 

 France, t. vi, pp. 245-285, 1893. 



