9 10 MICROBIAL DISEASES OF INSECTS 



combating the gipsy moth in the field. Many observations and tests 

 show that this disease did not occur in this country prior to 1917. 



SYMPTOMS. When a caterpillar contracts this new disease it ac- 

 quires a violent form of diarrhoea, loses its appetite, and finally ceases 

 to eat. The insect seems to lose all muscular coordination and usually 

 crawls to some elevated place, where it soon dies. After death it 

 hangs in a flaccid manner by its prolegs, with an appearance of death 

 from wilt. In contradistinction to wilt, however, the skin does not 

 rupture, but is so tough that one can pick up and stretch the animal 

 with considerable force before the skin breaks. 



CAUSAL ORGANISM. A microscopic examination of smears from the dead cater- 

 pillars readily precludes the possibility of wilt. Instead of polyhedra, large numbers 

 of a streptococcus, Streptococcus disparis are present. 



Strept. disparis has a diameter of less than i/*; chains of 3 to 4^ frequent in liquid 

 media; division in one plane; capsulated; non-motile; Gram-positive; stains 

 readily. 



Cultural characteristics are as follows: On nutrient agar slant, neutral, growth in 

 five days at 35 scanty, beaded, flat, glistening, smooth, white, opaque, no odor, 

 butyrous, medium unchanged. On potato agar slant, neutral, growth in five days 

 at 35 abundant, spreading, flat, glistening, smooth, white, opaque, odor absent, 

 butyrous, medium unchanged. Potato, growth moderate, spreading, flat, no odor, 

 butyrous, color of medium unchanged. Gelatin stab, growth best at top, beaded, 

 no liquefaction, medium unchanged. Nutrient broth, no ring or pellicle, slight cloud- 

 ing, clearing after fifteen days, slight sediment, no odor. Milk, coagulation de- 

 layed, extrusion of whey, color unchanged, no peptonization. Litmus milk, acid, 

 prompt reduction, coagulation delayed, extrusion of whey, no peptonization. Dun- 

 ham's peptone solution, clouding very slight, growth poor. Gelatin colonies, growth 

 slow, colonies very small and majority under surface, surface colonies round, slightly 

 convex, edge entire, no liquefaction. Nutrient agar colonies, growth slow, majority 

 of colonies under surface and oblong, surface colonies round, smooth, convex, edge 

 entire, internal structure finely granular, diameter 0.25 to 0.33 mm. Potato agar 

 colonies, growth rapid, majority of colonies under surface and oblong, surface 

 colonies round, smooth, convex, edge entire, internal structure finely granular, 

 diameter i to 1.5 mm. No ammonia production. Nitrates not reduced. Indol 

 and H 2 S not produced. Acid but no gas is formed in the following carbohydrate 

 broths used, extrose, levulose, saccharose, maltose, lactose, mannit, adonit, dulcit. 

 Facultative anaerobe. Best media for cultivation 1.5 per cent neutral potato agar, 

 and neutral nutrient bouillon containing i per cent of carbohydrate, especially 

 saccharose, maltose or mannit. Pathogenic to caterpillars of the American, Euro- 

 pean and Japanese races of the gipsy moth (Porthetria dispar L.}. Not pathogenic 

 to silkworms (Bombyx mori L.) and army worms (Cirphis unipuncta Ha worth) when 

 fed per os. Guinea pigs, rabbits and human beings when fed pure cultures per os 



