The mosquitos of two villages on the Kenya coast were studied over a period of two and a half years, which included years of very light, average and very heavy rainfall. A survey was made of the species occurring in the bush and in the houses, and in addition 24-hour biting catches were done and window-trap catches were examined to obtain information on the movement of species in and out of houses.Sixty five species were taken in net catches in the bush but only 19 were taken regularly; five (Taeniorhynchus uniformis (Theo.) and T. africanus (Theo.), Aëdes woodi Edw., Culex invidiosus Theo. and C. guiarti Blanch.) were abundant. In the houses, two species, C. pipiens fatigans Wied. and Aë. aegypti occurred regularly, the former being abundant and the latter not uncommon. Anopheles gambiae Giles and A. funestus Giles were seasonal; A. funestus appeared only after exceptionally heavy rain. The in-going window trap attracted only an occasional mosquito seeking shelter during the day and only six species were taken. Thirty species were found in the out-going trap but only seven occurred regularly. A. gambiae, A. funestus, T. uniformis, T. africanus and C. p. fatigans were most active during the hours of darkness, with the main activity in the four hours before dawn. Aë. aegypti had two waves of activity, in the four-hour periods before dawn and before sunset, respectively; the sunset peak was higher and the main activity probably occurred between 18 and 19 hr., as previously recorded for this species in Mombasa.Thirty five species were taken biting in the 24-hour catches in situations designated bush, house and compound, respectively. The biting cycles of A. gambiae, Aë. aegypti and C. p. fatigans have been compared in the three situations. The biting rhythm of each species was much the same in the different environments but the time and magnitude of the main peaks varied. In the case of Aë. aegypti, which probably includes two different forms, there is a marked difference in the magnitude of the evening peak in the bush and house. The biting cycles in the bush are given for A. squamosus Theo., T. uniformis, T. africanus, Aë. fryeri, Aë. metallicus (Edw.), Aë. albicosta (Edw.) and C. antennatus (Becker) and their occurrence in the other two situations is noted. The cycles of T. uniformis and Aë. fryeri agree with previous findings, but that of T. africanus differs from other cycles recorded for this species by having the main biting after midnight. The remaining species were rare, but one catch of 274 specimens of A. funestus was recorded.Resting mosquitos were more numerous in the second half of the year from August to December, a period of light rainfall and high temperatures. Biting mosquitos were more commonly taken, especially in the bush, in the second quarter of the year, during the main rainy season. The biting activity of some species increased in the houses in the second half of the year, when there are high winds, and biting in the bush was minimal.

At the time of writing, 1949, field work on mosquitoes has been carried on in Bwamba County, western Uganda, for a period of ten years, with very few intermissions. The topography and vegetation of this area have been described elsewhere (Haddow, 1945a). The main effort has centred round the search for forest vectors of yellow fever, but much work has also been done in native plantations, huts, etc. While genera such asAëdes and Taeniorhynchus have, inevitably, required special attention, records of all mosquitoes encountered have been kept throughout the investigation, whether or not they seemed likely to be involved in the local epidemiology of yellow fever. Certain sections of the work have already been published (Mahaffy & others, 1942; Haddow, 1945a, 1945b, 1945c, 1946 and 1948; Haddow & others, 1947; Haddow & Dick, 1948; Haddow & Mahaffy, 1949), but a great part of it has not as yet been submitted.

In this paper a list, with brief notes on prevalence, behaviour and habitat is given of 121 species, sub-species and varieties of mosquitos taken in the last 12 years during field work on the Kenya coast. Two species and one sub-species of the mosquitos found are not yet described. Notes on variation have been included for species that show interesting features in this respect and the distribution of the species in East Africa is also included where it is of interest.

Descriptions are given of 24-hour biting catches, made in and around Faza, a village on Pate Island, off the north-east coast of Kenya, East Africa.Aedes pembaensis Theo. was the predominant mosquito in these catches but fair numbers of Aedes mombasaensis Mattingly were also taken; the biting cycles of these two are discussed. Six other species were taken in small numbers.For Ae. pembaensis, biting cycles calculated on catches grouped for site, moon phases, neap tides and spring tides show that both moon and tide and light intensity influence the biting behaviour. Different but recurring patterns occur with various combinations of these factors.For Ae. mombasaensis, the cycles have a very constant biphasic pattern. Catches grouped for moon phases, tides and catch sites, as for Ae. pembaensis, show that more biting females are taken at neap tides than at spring tides. Two patterns of behaviour occur, one associated with spring tides and the other with neap tides. An even level of biting activity occurs during the night with intense and prolonged moonlight; otherwise moon-phase cycles have little effect on biting behaviour.It is felt that 24-hour biting catches can give useful information on behaviour patterns but it is desirable to have a long series of catches to analyse. For the purpose of calculating biting cycles, the results of catches showing similar modifications in behaviour should be treated separately.

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