MICROBIOLOGY OF DISEASES OF INSECTS 637 



flacherie; high humidity due to an approaching storm or to keeping the 

 worms enclosed in a practically air-tight cage prevents the transpira- 

 tion which is so necessary to the worm after the fourth molt. Too many 

 worms together often favors the progress of the disease. 



Control. — ^Pasteur instituted the following means of producing 

 healthy strains of the silk- worm; a small portion of the digestive cavity 

 of a moth was abstracted with a scalpel, mixed with a little water and 

 examined microscopically. If the moths did not contain tiie character- 

 istic microorganism, the strain they came from might unhesitatingly 

 be considered as suitable for seeding. The flacherie organism was as 

 easily recognized as the pebrine corpuscle, but the infection was more 

 difficult to prevent on account of the environmental conditions above 

 mentioned. 



Bactkrial Disease of Locusts 



Bacillus acridiorum — d'Herelle 



History and Distribution. — ^Tropical and subtropical countries 

 covering more than half the earth's surface suffer periodically from 

 plagues of locusts of different species. Famine and its attendant, epi- 

 demic disease, follow in their wake and decimate the regions invaded. 

 A bacterial epizootic has become a natural means of control. 



Bacillus acridiorum, the cause of the locust epizootic, was discovered 

 in Mexico in the state of Yucatan by F. d'Herelle. In 1909 a certain 

 mortality was noted among the swarms which arrived from the south 

 of the state where they winter; the following year the epizootic was 

 generalized and raged among a large number of bands; finally in 191 1, 

 all of the swarms which appeared were attacked, and in 191 2, the locust 

 invasion ceased. These particular locusts were the Schistocerca 

 fallens. 



Symptoms. — The locusts which are attacked by the natural disease, 

 present symptoms which are identical with those which are experimen- 

 tally inoculated or contaminated per os. After a time of incubation, 

 'which varies from one to forty-eight hours according to the virulence 

 of the bacillus, the age and individual resistance of the insect, and the 

 environment (temperature especially), at first the contents of the chyli- 

 fic stomach become liquefied and assume a dark color resembling 

 coagulated blood. The locust ceases to eat, becomes flabby, jumps 

 awkwardly and hides itself under tufts of herbage. The intestinal con- 



