Abstract
BackgroundAnopheles arabiensis is a key vector for the transmission of human malaria in sub-Saharan Africa. Over the past 10,000 years, humans have successfully cultivated grasses and altered the landscape, creating An. arabiensis favourable environments that contain excellent habitats for both larvae and adults. Sugarcane is the most expanding agricultural system in sub-Saharan Africa, and is linked to the increased threat of malaria in rural communities. The prolific production and wind dispersal of sugarcane pollen, together with standing pools of water, often provide, as a result of irrigation, a nutrient-rich environment for the offspring of gravid malaria mosquitoes.ResultsIn the present study, sugarcane pollen-associated volatiles from two cultivars are shown to attract gravid An. arabiensis in a still air two-port olfactometer and stimulate egg laying in an oviposition bioassay. Through combined gas chromatography and electroantennographic detection, as well as combined gas chromatography and mass spectrometric analyses, we identified the bioactive volatiles and generated a synthetic blend that reproduced the full behavioural repertoire of gravid mosquitoes in the Y-tube assay. Two subtractive odour blends, when compared with the full blend, were significantly more attractive. These three and four-component subtractive blends share the compounds (1R)-(+)-α-pinene, nonanal and benzaldehyde, of which, (1R)-(+)-α-pinene and nonanal are found in the attractive odour blends from rice plants and maize pollen. In pairwise comparisons, the rice synthetic odour blend was more attractive to gravid mosquitoes than either of the pollen blends, whereas the pollen blends did not differ in attraction.ConclusionsThe attraction of gravid females to sugarcane pollen volatiles demonstrated in this study, together with the previously found grass-associated volatiles, raise the potential of developing a bioactive chimeric blend to attract gravid malaria mosquitoes. This is discussed in relation to the development of novel and cost-effective vector control measures.
Highlights
Anopheles arabiensis is a key vector for the transmission of human malaria in sub-Saharan Africa
To increase our understanding of the oviposition ecology of An. arabiensis, and to enable the development of novel control strategies for this key vector, we have previously identified multi-component, behaviourally active, odour blends that reproduce the behavioural response of gravid mosquitoes to maize pollen [24] and rice plants [23] under laboratory and semi-field conditions
Gravid malaria mosquitoes respond to the odours associated with sugarcane pollen To investigate the behavioural response of gravid An. arabiensis to the volatiles associated with sugarcane pollen, the headspace extracts of individual sugarcane male flowers containing pollen from two cultivars, Coll 48 and EAK 71-402, were collected and tested in a two-port olfactometer (Fig. 1a) and an oviposition bioassay (Fig. 1b)
Summary
Anopheles arabiensis is a key vector for the transmission of human malaria in sub-Saharan Africa. The domestication, irrigation and continued cultivation of Poaceae grasses, such as maize, rice and sugarcane, provide larval nutrients, e.g. from pollen, that enhance the development and survival of Anopheles arabiensis larvae, above and beyond that provided by wild grasses [18, 19]. Such an association between the vector and crop suggests that mosquitoes have selectively adapted to these domesticated grass habitats [1, 10, 20,21,22], and is reflected in the odour-mediated response of gravid mosquitoes to these crops and their pollen [23, 24]
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