284 SCIENCE IN AFRICA 



impracticable or useless, although dusts of calcium arsenate were 

 fairly successful against young larvae ofHeliothis in Rhodesia. Cul- 

 tural measures, intended rather to check than to eradicate the 

 pest, seem to have given the best results under African conditions. 



Outbreaks of the American boll worm are largely determined by 

 weather, and the presence and condition of its alternative food- 

 plants. Where no winter crops are grown in irrigated areas, infesta- 

 tion is often comparatively slight. Recent investigations (Empire 

 Cotton Growing Corporation 1934a and i934b-38) on its biono- 

 mics suggest that the moths migrate not only from maize to cotton 

 as has generally been thought, but from cotton to maize, and that 

 they might, therefore, be diverted to maize under ordinary con- 

 ditions. The moths are associated with maize only when it is in 

 tassel, and planting should therefore be arranged to give overlap- 

 ping flowering periods. Cotton should be planted early, so that as 

 many bolls as possible may set before the moths come from the 

 maize, and during the critical period other farm crops should be in 

 the stage that attracts the moths. J. S. Taylor (1932) has investi- 

 gated this pest and its parasites in South Africa. There is some 

 possibility of breeding strains of cotton resistant to American 

 boll worm; in this progress has been made in Uganda. 



The chief cause of the spread of the pink bollworm is the exten- 

 sive transport of seed cotton for ginning. The enforcement of a 

 close season for cotton seems to be of the utmost importance. In 

 the Sudan (Cowland 1933) regulations providing for a dead sea- 

 son of several months and for the proper disposal of the crop and 

 storage of the seed have rendered the bollworm unimportant, 

 except in areas where it can survive in cotton stored for local spin- 

 ning and weaving. Disinfecting the seed with hot air has been 

 successful in Egypt and elsewhere. 



Measures against the red bollworm (Diparopsis castaneaHzimps.) 

 seem very unreliable, but in the Sudan irrigation before ploughing 

 has been found to destroy many of the pupae. It is generally 

 thought desirable to avoid the late planting of cotton, and traps 

 of standover cotton may reduce infestation. Smith (1933) has 

 carried out research on this pest in South Africa. Another bollworm 

 [Earias insulana Boisd.) is widely distributed and difficult to con- 

 trol. In the Sudan attempts have been made to encourage its 



