The practical importance of permanent and semipermanent habitats for controlling aquatic stages of Anopheles gambiae sensu lato mosquitoes: operational observations from a rural town in western Kenya

Abstract

SummaryControl of aquatic-stage Anopheles is one of the oldest and most historically successful interventions to prevent malaria, but it has seen little application in Africa. Consequently, the ecology of immature afrotropical Anopheles has received insufficient attention. We therefore examined the population dynamics of African anopheline and culicine mosquitoes using operationally practicable techniques to examine the relative importance and availability of different larval habitats in an area of perennial malaria transmission in preparation for a pilot-scale larval control programme. The study was conducted in Mbita, a rural town on the shores of Lake Victoria in Western Kenya, over 20 months. Weekly larval surveys were conducted to identify the availability of stagnant water, habitat characteristics and larval densities. Adult mosquitoes were collected indoors at fortnightly intervals. Availability of aquatic habitats and abundance of mosquito larvae were directly correlated with rainfall. Adult mosquito densities followed similar patterns but with a time-lag of approximately 1 month. About 70% of all available habitats were man-made, half of them representing cement-lined pits. On average, 67% of all aquatic habitats on a given sampling date were colonized by Anopheles larvae, of which all identified morphologically were A. gambiae sensu lato. Natural and artificial habitats were equally productive over the study period and larval densities were positively correlated with presence of tufts of low vegetation and negatively with non-matted algal content. The permanence of a habitat had no significant influence on larval productivity. We conclude that A. gambiae is broadly distributed across a variety of habitat types, regardless of permanence. All potential breeding sites need to be considered as sources of malaria risk at any time of the year and exhaustively targeted in any larval control intervention.

The molecular and cellular basis of olfactory-driven behavior inAnopheles gambiaelarvae

“…gambiae olfactory system, there is a paucity of information as to the molecular and cellular basis of olfaction in larval stages, in which it may be of potential importance in disease control. Paradoxically, despite being one of the historically most successful strategies for mosquito control (2) and prevention of human malaria, the targeting of mosquito larvae or larval habitats around human dwellings is sparsely implemented in Africa and other malaria-endemic regions (3). Furthermore, the simplicity of insect larval olfactory systems makes them excellent models to study olfactory signal transduction and coding.…”

Influence of soil quality in the larval habitat on development of Anopheles gambiae Giles

“…Adult mosquitoes are difficult to control since they can fly relatively long distances and survive in a range of microhabitats, including houses, vegetation, holes in rocks and soil, among others (Gilles and Warrell 1993). Nevertheless, the adult stage has been the main target in mosquito control for decades (Fillinger et al 2004). Larval control has only been taken into account recently, and is still underestimated in many areas .…”

A breeding site model for regional, dynamical malaria simulations evaluated using in situ temporary ponds observations

“…Mosquitoes may exploit any available water for oviposition, natural or man-made (Imbahale et al, 2011;Fillinger et al, 2004), permanent or temporary (Fillinger et al, 2004), clean or polluted (Sattler et al, 2005;Awolola et al, 2007;Chinery, 1984) and of various sizes from hoof-prints of animals to the edges of large water bodies (Sattler et al, 2005;Mutuku et al, 2006b;Imbahale et al, 2011), although individual species have preferences of habitat type. For example, Anopheles gambiae complex mosquitoes, the principal malaria vector in Sub-Sahara Africa prefer temporary, sunlit water bodies for their breeding, which become abundant during the rainy season (Mutuku et al, 2006a;Minakawa et al, 2004), although their larvae have also been found in polluted waters (Imbahale et al, 2011;Awolola et al, 2007;Sattler et al, 2005).…”