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



259 



along with those of A. costalis, A. marshalli, S. fasciata, and S. luteocephala. 

 In the Northern Territories of the Gold Coast, Ingram (Bull. Ent. Res. x, 1919, p. 50, 

 et seq. ) found amongst trees near dwellings that those which showed rot-holes most 

 commonly were the flamboyant, wild fig trees, mangos, silk-cotton trees, *' dawa 

 dawa " (Parkia higlobosa) and tamarind. Larvae of S. fasciata, C. invidiosus, and 

 S. ? unilineata were found ; also C. nebulosa at Kintampo in North Ashanti. 



In other countries, the larvae of Ochlerotatus (Culicada) ornatus, Mg., have been 

 found in the horse chestnut (Aesculus hippocastanum) in Italy, and those of 

 Stegomyia sp. in a tree fork and in cut bamboos at Hanoi, Tonkin. In the Lagos 

 list no Anophelines appear, but in Freetown A. costalis, and in Accra both A. costalis 

 and A. marshalli appear as facultative tree-breeding species. 



In India A. culiciformis, Cogill, and A. plumbeus, Stephens (syn. A. barianensis, 

 James, and A. nigripes, Staeger) are believed to be essentially tree-hole mosquitos 

 (Christophers, Ind. Journ. Med. Res. iii, pt. 3, Jan. 1916, and Christophers and 

 Chand, ibid. pt. 4). The last-named, which has also been obtained from trees in 

 Mesopotamia, freely enters houses and sucks blood. The related American 

 species A. barberi, Coquillet, has a similar habitat. The larvae of A. plumbeus 

 have been found in tree-holes both in England (Burnham Beeches, Liverpool, etc.), 

 Scotland (Culross), and Ireland (Armagh, Derry, and Louth), in beech, horse- 

 chestnut and elm. In Liverpool district and Cheshire A. plumbeus, either alone 

 or in association with Ochlerotatus geniculatus, 01., have been obtained in large 

 numbers from tree-holes, the trees found most favourable to the insects being the 

 elm, horse-chestnut and sycamore (Blacklock find Carter, Ann. Trop. Med. Parasit. 

 xiv, pp. 115-126). In Edinburgh this species was found fairly abundantly some 

 years ago in a weU-wooded residential district on the south side of the town. The 

 larvae were not found, but in the absence of any discovered source the suspected 

 tree-holes were cemented up, with apparent reduction of the mosquito in the 

 neighbourhood. 



Mosquitos breeding in Wells. 



In the period 1914 to 1918 inclusive, 12 species have been obtained as larvae 

 from wells. The 265 samples from which determination of the imagines was 

 made yielded results shown in the following table : — 



Table IV. 



Species of Mosquito. 



Number of Occasions. 



Percentage. 



Stegomyia fasciata 





136 



51-3 



Culex decens 









39 



14-7 



Anopheles costalis . . 









35 



13-2 



Ochlerotatus irritans 









18 



6-8 



Culiciomyia nebulosa 









12 



4-5 



Culex tigripes 









6 



2-3 



,, fatigans 









6 



2-3 



,, grahami 









5 



1-9 



„ duttoni 









3 



1-1 



Uranotaenia annulata 









2 



•7 



Culex consimilis 









2 



•7 



„ insignis 









1 



•4 



■ 





Total 



265 





