642 MICROBIAL DISEASES OF INSECTS 



this mode of contagion; the epizootic little by little regains its normal activity. A 

 rain of short duration, to the contrary, seems to favor the progress of the disease. 



A curious phenomenon takes place when a band of infected nymphs meet a river 

 in the course of their route. On the near bank is found an actual heap of cadavers, 

 on the opposite bank likewise but they are very much less in number. The epi- 

 zootic.seems to be completely checked; it recommences only after several days when 

 it takes its normal course. This is explained by the fact that all the nymphs al- 

 ready badly diseased are not strong enough to make the necessary effort to cross the 

 stream and die without surmounting the obstacle; those which were only slightly 

 diseased could pass it but were so enfeebled by their effort that they died on the 

 opposite bank. Thus the colony which pursues its march is composed only of 

 healthy insects and of several nymphs in which the infection has hardly begun. 



The duration of an epizootic is impossible to predict for all species of insects and 

 under all conditions; as a general rule it will last several days, most often several 

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

 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 tb 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 froin 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 pollens). — 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 maroccanuL — 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.) 



