182 CHAPTER XI 



precaution to prevent their introduction. Insect pests, how- 

 ever, although less serious than in Egypt and America, lay a 

 heavy toll on South African production. 



Cutw^orms {{Agrotis spp.) are apt to injure the seedlings 

 until these are about a foot in height. The Cotton Aphis, 

 although prevalent, is not looked upon as a serious pest. 



Several leaf -eating caterpillars, among these the Prodenia 

 Caterpillar, are found ; the damage done varies, but on the whole 

 is seldom really serious. 



Three boll worms are found and are considered to be the 

 most serious pests of cotton in South Africa. The grubs eat 

 holes in the bolls and then destroy the developing fibre and 

 seed. If attacked in the young stage, the bolls fail to mature 

 and fall off. Braine' gives the following description of these 

 boll worms : — " (a) The American boll worm (Chloridea 

 ohsoleta) : Caterpillar, greyish, brownish or greenish, dull, 

 without red bands or stout spines ; a common pest not only of 

 cotton, but of lucerne, maize and fruit trees. It is also known 

 as the earworm of maize, (b) The Spiny boll worm (Earias 

 insulana) : The adult insect is a small moth, nearly an inch 

 across the expanded wings. The head, thorax and forewings 

 are bright pea green, with a varying dark patch of brown or 

 with three-angled marks of darker green. The caterpillar is 

 smaller than that of the American boll worm, brown, somewhat 

 hump-backed, with many spines, (c) The Sudan boll worm 

 (Diparopsis castarea) : The caterpillar is smooth, greasy look- 

 ing, yellowish, white or greenish, with red bands (pinkish 

 when young). Like the American boll worm, it pupates in the 

 soil." 



Several species of cotton stainers are found which, like the 

 Cotton Aphis, obtain their food by sucking the juices of the 

 plant. The chief damage caused by these insects is a dis- 

 colouration of the lint, which arises from the stainers when 

 crushed. 



There are numerous minor pests such as the Eoot gall 

 worm (Heterodera radicicola), scale insects, thrips, leaf -rollers, 

 fruit beetles, etc., which seldom cause severe injury to the crop. 



In countries where labour is very cheap, hand-picking for 

 some pests is often practised. The South African farmer can 

 combat these best by practising a rotation, winter ploughing 

 and frequent cultivation. 



A number of fungous and bacterial diseases are found ; 

 fortunately the losses due to these in South Africa are in no 

 way comparable with those caused by the insect pests. The 

 following may be mentioned : — 



