46 



Velu (H.) & BouiN (A.). Essais de destruction de Schistocerca pere- 

 grina, Olivier, au Maroe, par I'emploi des cultures microbiennes 



{Coccobacillus acridiorum, d'H6relle). [Trials in destroying Schis- 

 tocerca jperegrina in Morocco, by the use of microbe cultures 

 {Coccobacillus acridiorum).] — Bull. Soc. Path. Exot., Paris, viii, 

 no. 9, 10th November 1915, pp 638-641. [Received 4th 

 December 1915.] 



A severe invasion of locusts may cause a loss of several millions of 

 pounds in Morocco. The Government of this French protectorate, 

 on the advance of the pest being notified from Agadir in the autumn 

 of 1914, decided to attempt control in 1915 by means of d'Herelle's 

 Coccobacilkis. Dr. Sergent supplied a very virulent culture to the 

 authors for the purpose. Many preliminary tests were made and an 

 area of about 540 square miles was infected on the right bank of the 

 lower reaches of the Oum-er-Rbia. Lack of plant and staff prevented 

 the production and spraying of large quantities of bouillon and this 

 led to a study of the natural means of intercontamination, which were 

 then employed to spread the epizootic. It was found that the virulence 

 varies with the temperature, the age of the inoculated locusts and the 

 age of the culture. A virus which kills in three to four hours at 

 77°-^5° F. requires 8-10 hours at 59°-68° F. A virus which, when 

 inoculated in the abdominal cavity, takes four hours to kill a locust 

 15 to 20 days old, requires 14 hours in the case of a locust from 30 to 40 

 days old. The virus keeps long enough to permit of its being used to 

 recommence the passages through a series of insects in order to 

 increase its virulence. Cannibalism is the principal factor in 

 contamination, and in infected swarms this assumes considerable 

 importance, as all the weak and sickly individuals become the prey 

 of the healthy and strong. This explains the rapid transmission of 

 the disease and the difficulty in checking results owing to the almost 

 complete lack of dead bodies. It is possible to create an epizootic 

 centre by placing even a very small number of infected locusts in a 

 swarm of healthy ones. This artificial method allows of dissemination 

 in an entire district being effected far more quickly than by the natural 

 means of contamination. Epizootics thus created are far from being 

 instantaneous in their effects. After an incubation period of varying 

 duration, there is a period in which the incidence of the disease and 

 the mortality are sometimes considerable (disease : 90 per cent. ; 

 mortality— in 48 hours, in a cage : 60 per cent.). The swarms 

 advance less speedily and sometimes either stop or break up into two 

 portions : one, composed of the more resistant individuals continues 

 to go on, while the other, comprising the sick and weak individuals, 

 stops. The epizootic then spreads to other swarms up to the end of 

 the development of the locusts or even after the last moult. The 

 effect of the disease then decreases, the incidence remaining constant, 

 but the mortality falling till it sometimes disappears, either owing 

 to an increase of resistance in the individual or by reason of a 

 weakening of the virus. On this account, locusts are at last met 

 with which show a considerable tolerance. They suffer from the 

 specific diarrhoea, but do not die. In these individuals, it is chiefly 

 in the digestive tube that the Coccobacillus is found. Its presence 

 in other parts is either rare or non-existent. Success depends mainly 

 on the time at which infection takes place, the most suitable period 



