The mosquitos of Zaria Province, Northern Nigeria

Abstract

A general survey of the species of Anopheles in Zaria Province, Northern Nigeria, carried out between June 1957 and December 1958, was designed primarily to ascertain the bionomics of actual and potential vectors of malaria there. The studies, which were centred upon the four principal domestic Anophelines, A. gambiae Giles, A. funestus Giles, A. nili (Theo.) and A. wellcomei Theo., were carried out by making regular floor-sheet collections and entranceand exit-trap catches in native huts, together with biting catches inside and outside huts. Data on other Anophelines and Culicines, taken at the same time, were also recorded.The studies show that in this region, where malaria is holoendemic, all four species are endophagous to a greater or lesser extent although both A. gambiae and A. nili prefer to feed outside if a host is available. Only two species have been incriminated as vectors, A. gambiae, which had a sporozoite rate of between 4 and 7 per cent., and A. funestus with between 3 and 8 per cent., according to the season.Collections by floor-sheets and by catches at human bait showed that A. gambiae, A funestus and A. nili were predominantly wet-season species, although in one village area studied A. funestus also occurred in fairly high numbers throughout the dry season. A. wellcomei, on the other hand, was shown to be a predominantly dry-season species.By using traps and making collections with human bait, the entrance, exit and biting times of A. gambiae, A. funestus and A. nili were ascertained. The largest numbers of A. gambiae and A. funestus entered huts between 9.0 and 11.0 p.m. and left between 3.0 and 5.0 a.m., the maximum biting activity for A. gambiae being between midnight and 5.0 a.m., and for A. funestus between 11.0 p.m. and dawn. A. nili differed considerably from the other two species, having two peaks of maximum entry, between 9.0 and 11.0 p.m. and 1.0 and 3.0 a.m., the period of maximum exodus being between 1.0 and 5.0 a.m., with a peak of biting activity between 10.0 p.m. and 1.0 a.m. It was found that a very high proportion of the mosquitos caught leaving the huts was unfed; between 1.0 and 5.0 a.m., 64 per cent, of A. gambiae leaving, 63 per cent, of A. funestus and 30 per cent, of A. nili were unfed.Apart from the four domestic species of Anopheles mentioned above, the only other anthropophilous species which could be described as common in the vicinity of Kaduna were A. coustani Lav., A. theileri Edw., A. flavicosta Edw. and A. rufipes (Gough). A. implexus (Theo.) is recorded from Nigeria for the first time.The commonest species of Culicines taken at human bait during outside night collections were Mansonia africana (Theo.), M. uniformis (Theo.), M. cristata (Theo.), Aëdes lineatopennis (Ludl.) and Culex poicilipes (Theo.). Of these, M. uniformis was by far the most regular and persistent biter throughout the year. M. africana, on the other hand, was only taken in any numbers during October.In an appendix, a list of 17 species of Anopheles (including 3 varieties), 65 of the CUlicinae and two of the TOxorhynchitinae known to occur in Zaria Province is given, with notes on their distribution and bionomics.