CRAB-HOLES, TREES, AND OTHER MOSQUITO SOURCES IN LAGOS. 



267 



(As the main object of the collection was to ascertain the relative prevalence of 

 S. fasciata, Anophelines are excluded, their numbers being always excessive during 

 the period covered ; two specimens of A. nili occurred amongst several 

 hundreds of A. costalis). 



Table VIII. 

 Adult Culicine Mosqiiitos in Native Houses, Lagos, July to September 1917. 



Species. 



No. of Specimens obtained. 



Percentage. 



Culiciomyia nehulosa 







83 



74-8 



OchJerotatus nigricephalus 







10 



9-0 



Culex decens . . 







5 



4-5 



,, grahami 







3 



2-7 



Ochlerotatus irritans . . 







3 



2-7 



Stegomyia fasciata 







3 



2-7 



Culex tigripes . . 







2 



1-8 



„ thalassiua 



Tot 



al 



2 



111 



1-8 



This list might be regarded as corroborating the remarks above on the influence 

 of the agho pot, and of the sanitary inspector, on the preponderance of Culicio7nyia 

 over Stegomyia, were it not that Ingram and Macfie warn us against accepting such 

 a collection (probably made chiefly in the evening) as evidence of the relative 

 absence of S. fasciata, a scarcity which is often demonstrable even in blocks where 

 its larvae are predominant, and for which a possible explanation is that this species 

 " whilst -entering houses to obtain a feed of blood, does not roost indoors " (Bull. 

 Ent. Res. vii, p. 173). More abundant collections under proper conditions of 

 observation should settle this point, but material of this nature from Lagos is at 

 present insufficient. There seems no doubt that under native social conditions 

 in Lagos C. nehulosa has become a highly domesticated species, and this habit 

 along with its actual abundance suggests the need for a study of its bionomics 

 and potentialities as a possible carrier of disease. 



Many mosquitos have been captured for identification at various times in the 

 European quarters to the east of the Race-course and around the Golf-course. The 

 following list (p. 268) shows one such classified collection, in which note was taken 

 of the numbers obtained during one month only ; in a total of 1,682 specimens 

 a rich mosquito fauna is represented including 26 species. 



June is the month of greatest rainfall and A. costalis preponderates. Much 

 has been done since then in the area in question in the way of filhng hollows and 

 draining. The abundance of crab-holes in the locality no doubt influences the order 

 of precedence amongst the Culicines. 0. domesticus takes a comparatively high 

 place, though its larvae have only once been discovered in a neighbouring swamp ; 

 they have previously been found in borrow-pits by the railway on the mainland. 



A smaller collection of 150 mosquitos from the same houses, covering the period 

 15th May to 21st July, 1917, is shown overleaf ; 16 species are represented. 



