658 MICROBIAL DISEASES OF INSECTS 



Methods of Infection. — A very common method of infection is 

 due to the habits of the silk-worms crawling over one another. When 

 a worm moves across a diseased worm, its claws cut through the tegu- 

 ment and become contaminated; in its progress it inoculates other worms 

 by means of its soiled fangs. The greatest source of contagion, however, 

 is the excreta which fall on the food of the worms. Luckily this infec- 

 tious material on being exposed to light and air, becomes rapidly at- 

 tenuated. However, the causal organism is not so attenuated when 

 within the egg; it passes the winter in a latent state and develops along 

 with the worm, multiplying within its body and altering more or less 

 profoundly the conditions of existence. 



Control. — If moths are not seriously diseased, their eggs will 

 / always furnish several healthy larvae and if these are isolated as soon 

 as they hatch out and are kept and bred under sanitary conditions, a 

 race of worms free from corpuscles can soon be obtained. This has 

 been found to be the most, effective method of combating pebrine. 

 Excessive heat skps the vitality of the silk- worm and makes it ready 

 prey to disease. Open air cages resulted in much hardier, more active 

 worms. 



