AND PROBLEMS OF SOUTHERN NIGERIA. 199 



Failing a power spraying machine, a number of machines which can be wheeled 

 between the rows of plants should be used. The most recent work on insecticides 

 goes to prove that lead chromate is a most easily handled and effective poison. 



Native Cottons. — Before native cottons at Ibadan can be treated as suggested 

 above, two courses are open : — (1) The obtaining, by selection, of a smaller native 

 variety ; (2) the topping and trimming of the plants and widening the distance 

 between the drills. 



It remains to be shown by experiment whether the latter method, plus the 

 assistance of entomological treatment, would be preferable to the present method. 



Leaf-rolling' Caterpillars. 



Sylepta derogata, F. (Plate XXV, fig. 7), and Zehronia phenice, Cram. 

 (Plate XXV, fig. 5). 



Both insects are evidently wide-spread throughout the Colony, as specimens 

 have been obtained from both the Western and Eastern Provinces. It was 

 observed at Ibadan that S. derogata was particularly plentiful among cotton which 

 was planted near a small stream and overshadowed by a large number of palm 

 trees. The plants supported the caterpillars, while the moths lurked in great 

 numbers among the thick grass and weeds fringing the stream. In an area of 

 GOO square yards examined, every single cotton plant was attacked by the larvae, 

 and in most cases all the leaves were riddled and rolled. Z. phenice is most 

 usually found where okra {Hibiscus esculentus) is grown. 



The larvae of both species cut and roll the leaves into the shape of a 

 tent (Plate XXVII, fig. 1). In these shelters they feed on the inner rolls of 

 the leaf. 



Sylepta derogata is gregarious, and as many as 12 caterpillars may flourish in 

 one shelter ; the earliest time of appearance for the larvae in Southern Nigeria 

 was found to be 19th August 1911. Zehronia phenice was found first on the 7th 

 November 1911, but must be active before that; it was quite common during 

 April in the Eastern Province. The larvae are usually solitary. 



Sylepta, derogata is dealt with by Lefroy in " Memoirs of Department of 

 Agriculture in India, Vol. II., No. 6," and his account agrees with what has been 

 observed in Southern Nigeria. 



The eggs of Zehronia phenice have not been found. The larvae are green, 

 slightly larger than those of Sylepta derogata and not so wet-looking. The pupae 

 are brown and are found in a silken shelter spun in curls of the leaves. The 

 pupal period lasts from 6 to 1 1 days. 



The local food-plants are not known in the case of either species, nor are 

 there any exact data as to the number of eggs and generations, but the short 

 period of development indicates more than one generation and very rapid 

 multiplication. 



S. derogata is extensively parasitised by a species of Braconidae, and a fly of 

 the family TACHiNiDAEalso serves as a check (see under " Beneficial Insects ") ; 

 but the proportion of parasitised to unparasitised caterpillars has not yet been 

 ascertained. The only practical method of control is by spraying. 



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