288 SCIENCE IN AFRICA 



Cacao 



In West Africa, where cacao is the chief export crop, the plants 

 are infested by a large number of pests, two of which may be 

 regarded as of major importance. 



Thysanoptera of the genus Selenothrips, especially S. rubrocinctus 

 Giard, are widely distributed and are very destructive. It appears 

 that attack occurs under bad conditions of culture which can be 

 correlated with faulty water relations between plant and soil. 

 Control measures include cultural measures and the use of insecti- 

 cides containing resins (Kaden 1934). The other pests against 

 which special work has been necessary in the Guinea Gulf are 

 capsids of the genus Sahlbergella (Cotterell 1930). These bugs are 

 also destructive in the Belgian Congo. Experimentally, a nicotine 

 spray was successful in the Guinea Gulf area, but it was found diffi- 

 cut to get it generally employed, and both nicotine and other 

 effective sprays are littie used commercially. Insect pests of stored 

 cacao in the Gold Coast and elsewhere are mentioned later, but 

 one of these, a weevil [Araecerus fasciculatus De G.),is known also to 

 attack cacao in the pod in Tanganyika. The insect pests of cacao in 

 French West Africa, especially the Ivory Coast, together with pests 

 of other crops, are considered in a long paper by Mallamaire ( 1 934) . 



Miscellaneous 



Perhaps the most important of the pests of tobacco is the whitefly 

 (Bemisia) which is the vector of leaf-curl, a virus disease in South 

 Africa, Rhodesia, the Belgian Congo, Tanganyika, Nyasaland, and 

 Nigeria. A similar disease has been recorded from Java, where it is 

 transmitted by a species of Bemisia, not, however, the same species 

 as that which experiments at Amani have shown to transmit the 

 disease. It is thought by H. H. Storey (1932) that the species used 

 at Amani is the same as that which is a vector in Rhodesia (B. 

 rhodesiensis Corb.). A species of Bemisia has also been proved by 

 Golding to transmit leaf-curl in Nigeria. In Rhodesia sprays of 

 tobacco extract and Bordeaux mixture have been tried as control 

 measures (Mossop 1932a), but the best control appears to have 

 been established by legislation which requires all tobacco lands to 

 be cleaned of plants by August ist each year, thus leaving no reser- 

 voirs for the virus. 



