xMICROBIAL DISEASES OF INSECTS 917 



weeks, rarely several months. The duration of an epizootic, however, is of little 

 importance; the object is to cause such a reduction in the number of the locusts that 

 these insects will cease to be a plague. 



To spread the epizootic to great distances, care should be taken to infect the 

 winged adults. Some species of locusts are more sedentary than others, it follows 

 that the more sedentary a species is, the more necessary to multiply the foci of 

 infection. 



In order to ascertain whether the epizootic is progressing, gather one hundred 

 locusts from different parts of the swarm and by pressing their abdomens, see how 

 many show the characteristic diarrhoea. Those insects showing diarrhoea one day 

 will be dead the next. 



Certain peculiarities were observed during the course of an epizootic. In swarms 

 infected a little while before egg-laying, numerous females lay eggs which never 

 reach maturity; others never reach the laying stage and the eggs are transformed 

 within the body to a blackish mass. Such bands were annihilated several days 

 afterward. In bands of nymphs infected several days before the last molt are found 

 numerous abnormal adults with poorly developed wings only half their ordinary 

 length which prevent them from flying, and further a microscopic examination of 

 the genital organs shows complete atrophy. 



SUSCEPTIBLE INSECTS. I. Acridians. B. acridiorum should be 

 pathogenic for all acridians. The following species are susceptible: 

 Schistocerca americana (or pallens). Natural epizootic in Yucatan in 

 1908-1911, induced in the Argentine Republic in 1912. 



Caloptenus sp?. Epizootic induced in December 1912 in the region 

 of Rio Negro, Argentine Republic. 



Stauronautus maroccanus. Epizootic induced in 1913 in Algeria 

 in the province of Oran, and in the isle of Cyprus. 



Schistocerca paranensis is killed by B. acridiorum. (Argentine Re- 

 public.) 



Gryllns pennsyhanicus , one of the common field crickets is sus- 

 ceptible. (DuPorte and Vanderleck). 



Zonocercus elegans, the so-called "elegant grasshopper' 3 of South 

 Africa, a non-migratory species, was used in inoculation experiments 

 with this bacillus. It was concluded that this disease at best could 

 be employed only as a supplementary measure in dealing with the inva- 

 sion of these insects under conditions that prevail in South Africa. 



The Philippine locust, Pachytylus migratoroides, has given negative 

 results with B, acridiorum. (Mackie). 



II. ANTS. A species of small ant near Paris was annihilated in 

 1911 by B. acridiorum. 



