Abstract
BackgroundMost odour baits for haematophagous arthropods contain carbon dioxide (CO2). The CO2 is sourced artificially from the fermentation of refined sugar (sucrose), dry ice, pressurized gas cylinders or propane. These sources of CO2 are neither cost-effective nor sustainable for use in remote areas of sub-Saharan Africa. In this study, molasses was evaluated as a potential substrate for producing CO2 used as bait for malaria mosquitoes.MethodsThe attraction of laboratory-reared and wild Anopheles gambiae complex mosquitoes to CO2 generated from yeast-fermentation of molasses was assessed under semi-field and field conditions in western Kenya. In the field, responses of wild Anopheles funestus were also assessed. Attraction of the mosquitoes to a synthetic mosquito attractant, Mbita blend (comprising ammonia, L-lactic acid, tetradecanoic acid and 3-methyl-1-butanol) when augmented with CO2 generated from yeast fermentation of either molasses or sucrose was also investigated.ResultsIn semi-field, the release rate of CO2 and proportion of An. gambiae mosquitoes attracted increased in tandem with an increase in the quantity of yeast-fermented molasses up to an optimal ratio of molasses and dry yeast. More An. gambiae mosquitoes were attracted to a combination of the Mbita blend plus CO2 produced from fermenting molasses than the Mbita blend plus CO2 from yeast-fermented sucrose. In the field, significantly more female An. gambiae sensu lato mosquitoes were attracted to the Mbita blend augmented with CO2 produced by fermenting 500 g of molasses compared to 250 g of sucrose or 250 g of molasses. Similarly, significantly more An. funestus, Culex and other anopheline mosquito species were attracted to the Mbita blend augmented with CO2 produced from fermenting molasses than the Mbita blend with CO2 produced from sucrose. Augmenting the Mbita blend with CO2 produced from molasses was associated with high catches of blood-fed An. gambiae s.l. and An. funestus mosquitoes.ConclusionMolasses is a suitable ingredient for the replacement of sucrose as a substrate for the production of CO2 for sampling of African malaria vectors and other mosquito species. The finding of blood-fed malaria vectors in traps baited with the Mbita blend and CO2 derived from molasses provides a unique opportunity for the study of host-vector interactions.
Highlights
Most odour baits for haematophagous arthropods contain carbon dioxide (CO2)
Laboratory findings indicated that higher catches of An. gambiae mosquitoes were recorded in traps baited with CO2 combined with skin emanations or ammonia plus L-lactic acid than CO2 alone [9]
The objectives of this study were to: (a) determine average release rates of CO2 produced by fermentation of different quantities of molasses and dry yeast; (b) evaluate the effect of release rates of CO2 on behavioural responses of An. gambiae; (c) evaluate the effect of CO2 produced from molasses on attractiveness of An. gambiae to a previously charatecterized synthetic odour blend; (d) assess the effect of CO2 released from refined sugar and molasses on attractiveness of a synthetic odour blend to An. gambiae; and, (e) evaluate the effect of CO2 released from refined sugar and molasses on attractiveness of a synthetic odour blend to outdoorbiting malaria and other mosquitoes
Summary
The CO2 is sourced artificially from the fermentation of refined sugar (sucrose), dry ice, pressurized gas cylinders or propane. Carbon dioxide (CO2) is the cue that is responsible for activating and guiding mosquitoes towards vertebrate hosts [2,3,4]. For this reason CO2 is commonly added to traps in order to increase mosquito catches during surveillance and/or sampling exercises [5,6,7]. In The Gambia, addition of CO2 to synthetic odours substantially increased the catches of females of all mosquito species collected in MM-X traps [12,14]. In many recent studies CO2 has been incorporated in synthetic odour blends for sampling malaria vectors [16,17,18]
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