Species abundance, composition and colonization behaviour of Malaria vectors in a semi-arid ecosystem of Baringo District, Kenya

Abstract

Malaria is one of the public health problems facing people in many parts of Kenya including semi-arid areas. It is caused by an infectious bite of female Anopheles mosquitoes. To effectively implement malaria control program, the knowledge of colonization, resting behavior of the vectors and effect of distance between houses and breeding habitats on mosquito abundance is required. This research set out to determine seasonal dynamics, outdoor resting habits and colonization of larval habitats by Anopheles vectors of malaria. The study was conducted in Kamarimar village in Baringo District adjacent to Loboi swamp. Larval survey was conducted once weekly by making 10-20 dips per habitat using standard dipper (350 ml). Ten houses were sampled by use of Pyrethrum Spray Catches (PSC) once a week for adult mosquitoes and aspiration method once a fortnight. Data was analyzed using SAS version 9.2. Mosquito breeding habitats comprised pan dams, ditches, marshes and canals. Marshes were relatively productive larval habitats and produced 35 out of the total 74 larvae collected in the dry season. However, no larvae were collected from canals. Pan dams, ditches and culverts produced 28, 9 and 2 Anopheles larvae respectively. Out of 281 Anopheles larvae collected from all the breeding habitats, 207 were collected during the rainy season. An. gambiae was found to breed in pan dams and ditches in both seasons and were constantly available during the rainy season in which 91 larvae were collected while the dry season realized only 22 larvae. An. funestus larvae were few but during the dry season, 21 larvae were collected from the swamp marshes and pan dams while in the rainy season, only 9 larvae were collected. The larvae of An. gambiae and An. funestus were rarely detected in the canals. Altogether, 2488 adult Anopheles mosquitoes were collected indoors of which 1166 were An. gambiae, 63 An. funestus, 11 An. coustani and 1248 An. pharoensis. 115 Anopheles mosquitoes were collected outdoors including most potential vectors of malaria. 2019 (81 %) Anopheles mosquitoes were collected during the rainy season while 463 (19%) were collected in the dry season. The effect of distance between a house and a breeding habitat on natural logarithm transformed mosquito numbers was significant, r =5.48, df =1, P =0.026. There also was a difference in mosquito abundance between outdoor habitats, i =29.87, df =2, p < 0.0001. A fitted Poisson regression revealed that interaction between seasons and habitats was significant X2 =12.6, df=l, p =0.027. The findings of this study may be useful in a vector control program targeting resting and breeding habits of malaria vectors as a way of controlling their population