Anopheles larval species composition and characterization of breeding habitats in two localities in the Ghibe River Basin, southwestern Ethiopia

Abstract

Background: Documentation of the species composition of Anopheles mosquitoes and characterization of larval breeding sites is of major importance for the implementation of larval control as part of malaria vector control interventions in Ethiopia. The aims of this study were to determine the Anopheles larval species composition, larval density, available habitat types and the effects of related environmental and physico-chemical parameters of habitats in the Ghibe River basin of southwestern Ethiopia. Methods: Anopheles larvae were sampled from November 2014 to October 2016 on a monthly basis and 3rd and 4th instars were identified microscopically to species. The larval habitats were characterized based on habitat perimeter, water depth, intensity of light, water current, water temperature, water pH, water turbidity, distance to the nearest house, vegetation coverage, permanence of the habitat, surface debris coverage, emergent plant coverage, habitat type and substrate type. Results: In total, 9277 larvae of Anopheles mosquitoes and 494 pupae were sampled from borrow pits, hoof prints, rain pools, pools at river edges, pools in drying river beds, rock pools, tire tracks and swamps. Anopheles larval density was highest in pools in drying river beds (35.2 larvae per dip) and lowest in swamps (2.1 larvae per dip) at Darge, but highest in rain pools (11.9 larvae per dip), borrow pits (11.2 larvae per dip) and pools at river edges (7.9 larvae per dip), and lowest in swamps (0.5 larvae per dip) at Ghibe. A total of 3485 late instar Anopheles mosquito larvae were morphologically identified. Anopheles gambiae sensu lato was the primary Anopheles mosquito found in all larval habitats except in swamps. Temperature at the time of sampling and emergent vegetation, were the most important variables for Anopheles mosquito larval density. Anopheles gambiae density was significantly associated with habitats that had smaller perimeters, were sunlit, had low vegetation cover, and a lack of emergent plants. Generally, Anopheles mosquito larval density was not significantly associated with water pH, water temperature, water turbidity, algal content, and larval habitat depth. Conclusion: Different species of Anopheles larvae were identified including An. gambiae s.l., the main malaria vector in Ethiopia. Anopheles gambiae s.l. is the most abundant species that bred in most of the larval habitat types identified in the study area. The density of this species was high in sunlit habitat, absence of emergent plants, lack of vegetation near habitat and habitats closer to human habitation. Rainfall plays a great role in determining the availability of

Geographically extensive larval surveys reveal an unexpected scarcity of primary vector mosquitoes in a region of persistent malaria transmission in western Zambia

“…gambiae s.l. to breed in close proximity to human settlements [50,51], and limit dispersal from these blood sources [31]. The range of aquatic habitats surveyed in our study encompassed streams and large, permanent and heavily vegetated larval habitats typically associated with An.…”

Larval habitats of Anopheles gambiae senso lato (Diptera-Culicidae) in Anger Gute resettlement villages, western Ethiopia

“…In line with this study, An. gambiae s.l.larvae were found to be the most abundant in rain pool habitats during the rainy season and in stream and river edge pools during the dry season in Ethiopia [19,20,22,23,27] and elsewhere in Africa [24].…”

“…gambiae s.l. breeds in sunlit rain water pools that were free of vegetation during the wet season [31,32] and in residual pools along drainage systems in dry season [16,19,22,23]. The mosquito larvae preferred vegetation free rain pools that were located along footways and roads than elsewhere in the study setting due to the influence of fast growing standing vegetation and associated fauna that might act as larval predators [32,33] However, in dry season, mosquito breeding sites are limited to drainage areas such as streams, rivers and lakes due to lack of rain water and the impact of desiccation.…”

“…The mosquito larvae preferred vegetation free rain pools that were located along footways and roads than elsewhere in the study setting due to the influence of fast growing standing vegetation and associated fauna that might act as larval predators [32,33] However, in dry season, mosquito breeding sites are limited to drainage areas such as streams, rivers and lakes due to lack of rain water and the impact of desiccation. But after onset of rain, the streams will increase and most larval habitats located along streams will be submerged by overflow of the stream water and succession of flora and fauna in the drainage areas [23,32].…”

Assessing Anopheles Vector Species Diversity and Transmission of Malaria in Cross-Border Areas of Côte d'Ivoire

“…Overall, the larvae of An. gambiae grow in small, shallow, relatively clean and sunny water reservoirs (puddles of water, stagnant water) [14,15], and is more frequent in rain-dependent temporary breeding sites. An.…”