AND PROBLEMS OF SOUTHERN NIGERIA. 203 



The laboratory experiments show a heavy mortality among the larvae. The 

 somewhat artificial conditions ma}^ account for this, though two other exceedingly 

 interesting and important factors have been observed. These are cannibalism, 

 probably induced by unnatural conditions, and parasitism. With regard to the 

 latter point, it has already been mentioned that three species of Chalcids and 

 one Braconid were bred from larvae of these beetles. 



Keeping in view the shortness of the developmental period — about 20 to 25 

 days — and the length of the season when food is plentiful — August to November 

 — it is not too much to estimate that three generations are possible. 



Chilomenes vidua, Muls. 



The numbers of eggs noted in single clusters were 3, 4, 7, 14 and 21, and they 

 appear to hatch in about two days. 



The larvae are smaller than those of Chilomenes lunata, being, when full 

 grown, about half an inch long. They have many white spots upon a black 

 spiny skin. The active period of the larvae is probably about 9 to 10 days, 

 though from one case it would seem that 15 days may be taken. The pupal 

 period takes four days. 



There was a heavy mortality among the larvae in the laboratory, but there 

 were no evidences of parasitism. They were not observed to feed on any insects 

 except the cotton green fly, and the activities of these two Chilomenes have kept 

 the Aphis well under control. 



Hover Flies (Syrphidae). 



Three species. Paragus borbonicus, Mcq., Syrphus aegyptius, Wied., and S. 

 nasutus, Mcq., were found at Ibadan, all of which are widely distributed over 

 Africa. The flies themselves have always been obtained in the field by netting 

 as they hovered over the cotton plants. The larvae, which are quite common, 

 crawl among the green fly on the cotton and suck them, thus materially assisting 

 in their reduction. 



Small solitary eggs, white and sculptured, have been found and seen to hatch 

 among the green fly on the cotton leaves, but to which species the eggs belonged 

 was not ascertained. 



The larvae of Paragus borbonicus are of the typical shape, tapering to a point, 

 about -J- inch long, and spiny. Their colour is light green, with a large brownish 

 dorsal patch. The puparia are also spiny, and of a dirty light green colour. 

 The pupal period lasts about 8 days. 



It is very probable that the slim, smooth, soft green grubs, larger than the 

 larvae of Paragus borbonicus, which were found upon cotton, are the larvae of 

 Syrphus nasutus. The puparia are smooth and larger than those of the Paragus. 

 The pupal period was, in two cases, 5 and 8 days respectively. 



One species of the family Braconidae is parasitic upon the larvae of Paragus 

 borbonicus. 



Lacewing Flies. 



Two undetermined species of this group, Hemerobius sp. and Chrysopa sp., were 

 bred from larvae which were found preying upon Aphis gossypii. The small 

 brown Hemerobius is commoner than the larger green Chrysopa. 



