ENTOMOLOGY 281 



on veterinary and agricultural research in East Africa (1934a, 



1934b). 



In the following notes the different crops are treated in the same 

 order as in Chapter XII, where other aspects of crop research are 

 considered. Frequent reference is made to the results of researches 

 which fall into the botanical rather than the entomological field, 

 particularly to work on virus and other diseases which are trans- 

 ferred from host to host by insects. 



Cereals 



The typical native cereals such as millets and guinea corn seem 

 to have attained a partial balance with the pests of Africa. Insects 

 cause considerable local loss to such crops, but the fact that they 

 are grown in small plots renders dispersal difficult for the pests. 

 The extensive growing of cash-crops, particularly those recently 

 introduced and having no natural immunity to local pests, such 

 as maize and wheat, gives opportunities of which Africa's insects 

 have not been slow to take advantage. Most of the entomological 

 work has been concerned with maize which is grown far more 

 extensively than other introduced cereals. 



Several of the polyphagous insects such as Heliothis obsoleta and 

 Prodenia litura have some importance as pests of maize. But most 

 of the research on these two moths has been carried out in connec- 

 tion with cotton (see below). 



In South Africa the most persistent pest is the maize stalk-borer 

 {Busseolafusca Fuller) . The control measures usually recommended 

 are mostly cultural, and include top-dressing with derrisol, the 

 destruction of crop-refuse during the winter and the avoidance of 

 early planting. Creolyte, however, has been found to be a powerful 

 stomach poison and suspensions of it spread on the tops of the 

 maize have been very effective (Mally 1920, Ripley and Hepburn 

 1930, 1934). Busseola produces a second generation on sorghum 

 in South Africa, and trap-crops have been suggested as a possible 

 control measure. 



A virus disease of maize, known as streak disease, is common in 

 South and East Africa. Experiments at the Amani Research Sta- 

 tion, directed to the study of the fundamental nature of virus dis- 

 ease as exemplified in tropical crops, have shown, incidentally, 



