1917] Studies on Coccohacillus Acridiorum D'Herelle 



51 



After the twelfth lot there was little increase in virulence. 



Quite often several locusts would die within a very short 

 while after being injected. This was probably due to a pre- 

 viously weakened condition of the locusts which rendered them 

 less resistant to the septicsemic action of the coccohacillus. The 

 intestinal contents of those which died thus early were not as 

 virulent as those of the ones which died later. The following 

 table brings out this point: 



TABLE II. 



COMPARISON BETWEEN THE VIRULENCE OF THE INTESTINAL CONTENTS OF LOCUSTS 

 WHICH DIE VERY EARLY AND OF THOSE FROM THE SAME LOT WHICH DIE LATER. 



D. Insects Susceptible to the Disease. 



The pathogenicity of Coccohacillus acridiorum was tested for 

 all species of locusts and grasshoppers commonly occurring in 

 large numbers in this region. These were Melanoplus femur- 

 rubrum, M. bivittatus, M. atlanis, Dissosteira Carolina, Camnula 

 pellucida, Stenohothrus curtipe?inis and Xiphidium sp. All of 

 these insects proved to be susceptible. 



Gryllus pennsylvanicus, one of the common field crickets, 

 also died as a result of injection with the coccohacillus, and 

 several dead specimens of Nemobius spp. were found dead in the 

 field, doubtless as a result of eating the infected bran mash. 



Of insects other than the Orthoptera only two were tested, 

 the yellow bear caterpillar {Spilosoma virginica) and the potato 

 beetle (Leptinotarsa decemlineata) larvae and adults. The 

 caterpillars were all dead in less than forty-eight hours. The 

 number of inoculated potato beetles and their grubs which died 

 did not exceed the number dead in the check injected with dis- 

 tilled water, so we must conclude that this beetle was not 

 susceptible to the disease. 



