Abstract
BackgroundThe reproductive success and population dynamics, of Anopheles malaria mosquitoes is strongly influenced by the oviposition site selection of gravid females. Mosquitoes select oviposition sites at different spatial scales, starting with selecting a habitat in which to search. This study utilizes the association of larval abundance in the field with natural breeding habitats, dominated by various types of wild grasses, as a proxy for oviposition site selection by gravid mosquitoes. Moreover, the role of olfactory cues emanating from these habitats in the attraction and oviposition stimulation of females was analysed.MethodsThe density of Anopheles larvae in breeding sites associated with Echinochloa pyramidalis, Echinochloa stagnina, Typha latifolia and Cyperus papyrus, was sampled and the larvae identified to species level. Headspace volatile extracts of the grasses were collected and used to assess behavioural attraction and oviposition stimulation of gravid Anopheles arabiensis and Anopheles coluzzii mosquitoes in wind tunnel and two-choice oviposition assays, respectively. The ability of the mosquitoes to differentiate among the grass volatile extracts was tested in multi-choice tent assays.ResultsAnopheles arabiensis larvae were the most abundant species found in the various grass-associated habitats. The larval densities described a hierarchical distribution, with Poaceae (Echinochloa pyramidalis and Echinochloa stagnina)-associated habitat sites demonstrating higher densities than that of Typha-associated sites, and where larvae were absent from Cyperus-associated sites. This hierarchy was maintained by gravid An. arabiensis and An. coluzzii mosquitoes in attraction, oviposition and multi-choice assays to grass volatile extracts.ConclusionsThe demonstrated hierarchical preference of gravid An. coluzzii and An. arabiensis for grass volatiles indicates that vegetation cues associated with larval habitats are instrumental in the oviposition site choice of the malaria mosquitoes. Identifying volatile cues from grasses that modulate gravid malaria mosquito behaviours has distinct potential for the development of tools to be used in future monitoring and control methods.
Highlights
The reproductive success and population dynamics, of Anopheles malaria mosquitoes is strongly influenced by the oviposition site selection of gravid females
The objective of this study was to investigate anopheline larval occurrence and abundance in natural breeding habitats populated by four wild grass species: antelope grass, Echinochloa pyramidalis (Poaceae); hippo grass, Echinochloa stagnina (Poaceae); common cattail; Typha latifolia (Typhaceae); and papyrus reed, C. papyrus (Cyperaceae), and to correlate the behavioural response of gravid An. arabiensis and An. coluzzii to the natural volatiles collected from these grasses
Anopheles arabiensis was the most abundant species comprising more than 40% of the specimens in the study area, and was the only member of the An. gambiae sensu lato complex to be identified following polymerase chain reaction (PCR) analyses of 48 mosquito larvae
Summary
The reproductive success and population dynamics, of Anopheles malaria mosquitoes is strongly influenced by the oviposition site selection of gravid females. The most productive natural larval habitat types for Anopheles gambiae/Anopheles coluzzii and Anopheles arabiensis are transient puddles [1], often surrounded by short grasses [7, 9, 19, 20] Both of these major vectors in sub-Saharan Africa have been recorded in more stable water bodies, such as the littoral zone of lakes and in swamps [1, 19, 21,22,23]. The nature of the volatiles emitted from wild grasses and how they affect the behaviour of An. arabiensis and An. gambiae/ An. coluzzii has not been investigated to date
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