282 SCIENCE IN AFRICA 



that the Jassid bug, Cicadulina mbila Naude, and two other species 

 of Cicadulina are vectors of this disease of maize (Storey 1925). 



It is convenient to notice here experiments on the transmission 

 of mosaic and streak diseases between maize and suger-cane. In 

 the Transvaal a strain of mosaic was found that would not infect 

 sugar-cane, though virulent to maize and sorghum (Storey 1929). 

 In the case of streak diseases there are two distinct viruses, virulent 

 respectively to sugar-cane and maize, both transmitted by C. 

 mbila, and both producing permanent infections in the hosts to 

 which they are specialized. The cane virus produces only a mild 

 form of the disease in maize, whereas the maize virus produces only 

 a transitory infection of cane, from which the plant recovers 

 (Storey and McClean 1930). 



In Southern Rhodesia, in addition to the above-mentioned pests, 

 the young maize plants are subject to attack by Snout Beetles 

 ( Tanymecus destructor MshL, and Sy states exaptus Mshl.) (Jack 1 935b) 

 Cutworms, wireworms, crickets, and grasshoppers, most of which 

 can be poisoned, are also troublesome. More difficult is the prob- 

 lem presented by the outbreaks of white grub [Eulepida mashona 

 Arrow), which seems to be specially associated with ground of 

 which the humus content has been artificially increased, as men- 

 tioned in the annual report of the Chief Entomologist, Mr. R. W. 

 Jack (1935b). 



Oil-seeds 



The polyphagous pests of cotton, Heliothis obsoleta and Prodenia 

 litura, do a certain amount of damage to groundnuts in various parts 

 of Africa, but the central problem of entomological research is the 

 rosette disease. During the last few years many experiments have 

 been made and at least two insects have been shown to be vectors. 

 Aphis laburni Kalt. has been found to transmit the virus experi- 

 mentally (Trochain 1931, Storey and Bottomley 1928), and this 

 aphid is found in association with the disease in Gambia, Senegal, 

 South Africa, Sierra Leone, Nigeria, and Uganda. In French 

 West Africa sprays of kerosene and soap free infected plants from 

 aphids and allow them to recover at least partially, but observa- 

 tions elsewhere in West Africa, especially in Sierra Leone, do not 

 confirm this result (Bouffil 1933). The French investigators have 



