2gO SCIENCE IN AFRICA 



successful (Ripley and Hepburn 1935). There also, the codling- 

 moth is being controlled by spraying, trapping, and hand-picking 

 (Pettey 1932). In the less civilized parts of Africa, however, even 

 ordinary simple methods of chemical control are beyond the 

 resources of the cultivators, and the problem is thus in most cases 

 rendered far more difficult because cultural methods of control, 

 which include breeding resistant strains, have to be devised, and 

 these must at the same time be fitted in with agricultural practice. 

 For crops recently introduced, closer attention is necessary. As an 

 example of this, investigations on the pests of tea in Nyasaland may 

 be mentioned (Smee 1928, Smee and Leach 1932). 



In the Union of South Africa parasites have been used in the 

 biological control of pests as in the case of the eucalyptus snout- 

 beetle, a parasite of which was brought by Mr. Tooke from Aus- 

 tralia and has led to complete control. Attempts have been made to 

 control the citrus mealy bug [Pseudococcus citri) with the Cryptolaemus 

 ladybird beetle and the woolly aphid with Aphelinus mali (Smit 

 1934b). In 1935 Mr. G. A. Hepburn began work on parasites of 

 the wattle bagworm imported from Madagascar. In South Africa 

 also work is in progress on the biological control of prickly pear 

 with Cactohlastis cactorum. This is in charge of Dr. Pettey, who has two 

 entomologists and several assistants at the stations of Uitenhage and 

 Graaff Reinet. 



Termites 



The probable effects of termites on soils, both in improving fer- 

 tility by aeration and in reducing fertility by destruction of the 

 grassland cover and in increasing erosion, and even perhaps in 

 consuming humus, have been discussed in Chapter V. In view of 

 the enormous numbers of these insects in all parts of Africa south 

 of the Sahara, their influence on agriculture and the serious 

 damage which they occasion to buildings, the amount of research 

 carried out on them seems small. The few works that have been 

 published come from South Africa. Fuller (1921 and 1922) has 

 given a valuable account of the species with notes on the localities 

 in which they are known, their nests, etc. From the same author 

 (1924) we have an anatomical study of some species, and also an 

 account of experimental tests on the resistancy timbers. More of 



