161 



Bacot (A. W.). Report of the Entomological Investigation undertaken 

 for the Commission for the Year, August 1914 to July 1915.— Rept. 



Yellow. Fev. Commiss. {West Africa), London, iii, 1916, pp. 1-191, 

 27 figs., 29 plates, 9 charts. [Received ]4th August 1916.] 



This report falls into two sections, the first containing notes on the 

 distribution of mosquitos in Freetown and the second deahng with 

 the bionomics of Stegomyia fasciata. 



Adult mosquitos are comparatively rare in Freetown, the most 

 important species present being Cidiciomyia nebulosa and S. fasciata. 

 The larvae of the former occur in almost any damp or shaded position, 

 while those of the latter are well hidden in protected places. Hence 

 the necessity arises for continuous and careful search on the part of 

 the Sanitary Department. In the outlying areas of the town and in 

 the neighbouring villages much still remains to be done with regard to 

 drainage of surface water and the removal of breeding places. Anopheles 

 (Pyretophorus) costalis and A. (Myzomyia) funestus are more restricted 

 in distribution and breeding places, the former being found in rock and 

 gutter pools, the latter in isolated rock pools at tlie foot of the hills 

 east and west of Freetown. Uranotaenia ornatus and Eretmopodites 

 dracaenae are restricted to collections of water in the axils and central 

 whorl of leaves of certain plants. S. simpsoni, mainly occurring in 

 root holes, is sometimes found in similar situations, together with 

 S. fasciata and C. nebulosa. The use as a hedge plant of species of 

 Dracaena in which water collects should therefore be discouraged. 



The eggs of S. fasciata are always deposited on a film of water, never 

 on a dry surface. They are generally found at the margin of a pool, 

 etc., or on a partially submerged object. Those at the margin become 

 submerged during rainy periods. In a few cases eggs laid on the 

 surface of the water have been observed. Hatching can take place 

 when the egg is floating, attached to the margin just below the surface, 

 or resting on the bottom. Preliminary experiments showed that 

 hatching was dependent to a certain degree on external conditions, 

 among which desiccation, temperature and change of water acted as 

 stimuh on a certain proportion of the eggs. Submergence in a small 

 quantity of water appeared to increase the mortaUty among the eggs. 

 During the course of the same experiments, it was noted that the 

 period between the time of immersion of the egg and the time of 

 hatching, in cases in which no dry period intervened, could be pro- 

 longed for four or five months. A higher mortality was observed 

 among eggs which had been stored than among those which were 

 immersed immediately or soon after laying. The material on which 

 eggs are deposited appears to determine whether they will survive 

 or not during periods of drought. The effect of high and low tempera- 

 tures on the rate of hatching was observed. Cooling to temperatures 

 between 74° and 80° F. acted as a stimulus to hatching in most cases, 

 but a few eggs remained resistant. Coohng is probably the factor 

 which causes hatching when dried eggs are immersed or when fresh 

 water is added to developing eggs. A rise in temperature from 80° to 

 95° F. had Uttle effect on hatching. Eggs stored for 50 hours under 

 moist conditions hatched in the majority of cases within 30 minutes 

 after subsequent immersion ; those dried for one to seven days after 

 incubation hatched, when immersed, to the extent of 84 and 54 per 



