105 



THE EARLY STAGES OF WEST AFRICAN MOSQUITOS. N.—CULEX 

 DECENS, THEO. AND CULEX INVIDIOSUS, THEO. 



By J. W. S. Macfie and A. Ingram, 

 West African Medical Service. 



Both Culex decens and Culex invidiosus are widely distributed in British West 

 Africa. In the Gold Coast both have been taken in all the three divisions into which 

 the country is divided, namely, the Colony proper, Ashanti and the Northern 

 Territories ; the records at Accra showing the following distribution : — 



Culex decens. 



Colony — ^Accra, Cape Coast Castle. 



Ashanti — Kintampo, Kumasi, Sunyani. 



Northern Territories — Batiasan, Bawku, Binduri, Bole, Daweni, Dogan Kade, 

 Jefisi, Kalleo, Kpalgu, Lorha, Mayoro, Nandaw, Nandawh, Nasia, Navarro, 

 Pinna, Salaga, Sambolugu, Savelugu, Tamale, Tanina, Tiana, Tishi, Ulu, 

 AVa, Yaga, Zuaragu. 



Culex invidiosus. 



Colony — ^Accra, Akuse, Bibianaha, Koforidua, Nsawam, Sekondi. 

 Ashanti — Akrokerri, Bjere, Kumasi, Obuasi, Odumase, Sunyani. 

 Northern Territories — Bawku, Bole, Gambaga, Kugri, Lorha, Mahki's Zongo, 

 Navarro, Tumu, Turn, Wa, Zuaragu. 



So far as they go these records do not point to any cleavage in the areas of distri- 

 bution of the two mosquitos, both species having been collected in a number of the 

 same places. 



The majority of the records for the Northern Territories were made by one of us 

 (A.I.) during a tour undertaken in 1918, the observations made at this time suggested 

 that C. decens might be a domestic variety of C. invidiosus. Edwards (Bull. Ent. 

 Res. iii, p. 381), however, considers the two to be distinct. In the adult, he says, 

 ^' C. decens can be distinguished by the reddish thorax (that of C. invidiosus being 

 brownish), and (in the male) the banded abdomen. In the female the abdominal 

 banding is not constant ; the bands in C. decens are always narrow and may some- 

 times be interrupted." But he failed to detect any differences in the genitaUa of 

 the males (an observation which he repeated later. Bull. Ent. Res., v, p. 70), and was 

 unable to separate the larvae, considerations which led him to admit that it was 

 " quite possible that the two are really only forms of one species." 



We have compared a number of larvae and pupae of these mosquitos in an 

 endeavour to find some means of distinguishing them. We may say at once that we 



