912 MTCROBIAL DISEASES OF INSECTS 



BACTERIAL DISEASE or 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 1911, 

 all of the swarms which appeared were attacked, and in 1912, the locust 

 invasion ceased. These particular locusts were the Schistocerca 

 pollens. 



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- 

 tents next become liquefied; they are at first a clear yellow, later dark- 

 ening little by little until they are blackish in color. At this stage a 

 slight pressure upon the abdomen causes the liquefied intestinal con- 

 tents to issue from the anus and the characteristic diarrhoea reveals itself 

 on the vegetation which is fouled with the dejecta of the sick locusts. 

 Some hours afterward the locust falls upon its side and the legs move 

 spasmodically; the locust remains in this comatose state several min- 

 utes to several hours until death occurs. When the virulence of the 

 coccobacillus is very high, very often the chylific stomach only presents 

 the characteristic blackening; death occurs before the intestinal con- 

 tents have undergone a modification. After death the insect putrefies 

 very rapidly and the tegument becomes dark. 



