MICROBIOLOGY OF DISEASES OF INSECTS 655 



caterpillars are those of flacherie of the silk-worm. They soon stop 

 eating, become languid, usually crawl up on some object where they 

 remain motionless. In a few hours there drops from the mouth and 

 anus a dirty, blackish, foul-smelling liquid; they become more and more 

 flaccid, one leg after another looses its support and finally the cater- 

 pillar reduced to a black skin is found hanging Umply to tree trunks 

 and limbs, still holding on with one or two of its false feet or with the 

 anal claspers. After death their body tissues become degenerated so 

 rapidly that it is impossible to handle them; a slight touch breaks the 

 skin and a thin dark, offensive-smelling liquid flows out,' consequently 

 they can never be used for histological work. 



Causal Organism. — A filterable virus seems to be responsible for 

 the death of these caterpillars. It is filtered with dif&culty, however. 

 Bacteria are not responsible for this disease. Minute dancing granules 

 are observed in the Berkefeld filtrate, which may be etiologically sig- 

 nificant. No bacteria or polyhedral bodies are observed in the filtrate. 



Methods or Infection. — Infection naturally takes place through 

 the mouth by means of the food. Predisposition to the disease is se- 

 cured by giving the caterpillars food which has been placed in water 

 and renewed only every three or four days. This causes an increase in 

 the acidity of the leaves which in turn decreases, the alkalinity of the 

 caterpillar's digestive fluid. Before the visible outbreak of flacherie, as 

 an early symptom, a characteristic sweet odor is recognized in the 

 breeding cages which resembles that of withered lilac blossoms some- 

 what. Whenever this odor is noticeable, flacherie soon makes its 

 appearance, and as it progresses the odor increases proportionately. 

 (Fischer). 



Lack of food, which is necessarily brought about by the cater- 

 pillars themselves, causes them to lose their vitahty, thus producing a 

 greater susceptibility to the disease. Defoliation also exposes them 

 to the sun's rays which have the effect of converting the chronic into 

 the acute form of wilt. In lightly infested woodland this does not hap- 

 pen as the caterpillars can always find shade. Flacherie, however, 

 seems to be influenced by climate and weather conditions 

 less than any other caterpillar disease. 



Wilt is always prevalent among the older caterpillars; young cater- 

 pillars often live several days before succumbing to the disease. Female 

 caterpillars always succumb more readily to the wilt disease than the 



