656 MICROBIAL DISEASES OF INSECTS 



male; this may perhaps be due to the fact that they require a longer 

 time to mature than the male. Diseased females deposit egg clusters 

 reduced in size, which contain usually, embryos, incompletely or not 

 at all developed. In this case there are always found undeposited 

 eggs within the body of the female, which never occurs with healthy 

 moths. Genetic immunity of certain individuals is probable. Sub- 

 lethal doses of the virulent filtrate may produce active immunization. 

 Although probable, there is yet no definite evidence that wilt is trans- 

 mitted from one generation to another. 



Pathology of Wilt. — When a caterpillar dies of wilt, all of its 

 tissues are in a state of disintegration. The intestine is the last in- 

 ternal organ to disintegrate. A smear of the brown liquid from a dead 

 caterpillar examined microscopically with a high power lens wUl be 

 found to contain, besides -the elements of disorganized tissues, m5Tiads' 

 of highly refractive polyhedral bodies of various sizes. The average 

 polyhedron measures from i/i to 6/^ in diameter and is never regular as 

 are the silk-worm polyhedra. The significance of these bodies is not 

 known. However, they are believed to be reaction bodies belonging to 

 the highly differentiated albumins, the nucleoproteids. They may be 

 stages of the filterable virus but no evidence has been brought forward 

 to substantiate this view. It has been determined however, that no 

 diagnosis of wilt is vaUd unless polyhedra are demonstrated 

 microscopicaEy. 



The " Wipfelkrankheit" of the nun-moth in Germany is essentially 

 the same disease as that of the gipsy moth in the United States (Es- 

 cherich and Miyajima.) 



PiBEINE, AN InTECTIOUS DISEASE OE THE SiLK-WORM, Bombycis 



mori 



Nosema bombycis 



History and Distribution. — About the year 1853, anxious atten- 

 tion began to be given in the southern part of France to the ravages of 

 a disease among silk- worms which from its alarming progress, threatened 

 to issue in national disaster. Symptoms of this disease had been noted 

 as early as 1845. It finally became necessary to import seed (technical 

 term for eggs) for continuing the culture of the silk-worms. This was 

 procured first from Lombardy, but after one successful year the same 



