262 SCIENCE IN AFRICA 



cover other tropical African locusts. Scientific knowledge on this 

 subject is due in a large measure to the researches of Mr. B. P. 

 Uvarov, who originally worked out in Russia the basic idea of the 

 *phase theory'^ of locusts. In his capacity as a member of the Com- 

 mittee on locust control and as senior assistant in the Imperial 

 Institute of Entomology, Mr. Uvarov has been largely responsible 

 for the valuable reports of the committee. Uvarov has also sum- 

 marized the position in a short article (1934), so that only an 

 outline need be given here. 



International conferences on measures against locusts have taken 

 place in 1931, 1932, 1934, and 1936 (Conference, International 

 Locust, 1934), and it was agreed in 1931 that the Imperial Insti- 

 tute of Entomology should be the international centre for anti-locust 

 research in all Africa. Monthly reports are now sent in from every 

 affected territory except Abyssinia. These are all analysed and 

 plotted at the Institute, with the result that the annual surveys 

 prepared by Uvarov (Economic Advisory Council 1933-7) include 

 a most illuminating series of maps showing the movements and 

 incidence of each species. The accumulation of these data is 

 leading to conclusions concerning the location of the all-important 

 centres of dispersal of the three species. The suspected centres 

 are in sparsely inhabited and inaccessible areas, and in order to 

 locate them exactly and to investigate methods of early control, 

 intensive field investigation by entomologists devoted entirely to the 

 problem on hand is essential. This has been financed from funds 

 contributed half from British colonies and half formerly from the 

 Empire Marketing Board, and later from the Carnegie Corporation, 

 which enabled the following officers to be maintained in the field: 

 Mr. H. B. Johnston and Mr. D. R. Buxton in Uganda and neigh- 



' Uvarov proved that locusts in general show a fluctuation between two phases, 

 solitary and migratory, the latter appearing at intervals and dying down after a period 

 of intense activity. The solitary locusts live in restricted special environments, and 

 when they become too concentrated change into the migratory phase. Thus the 

 all-important task in locust control is to locate the centres where the solitary phase 

 can change into the migratory one. The locust cycle can be expressed in a diagram : — 



->^ Dissociating --v„^ 



/ ^ 



Migratory Solitary 



phase phase 



Congregating "" 



