Background: Mosquitoes that bite people outdoors can sustain malaria transmission even where effective indoor\r\ninterventions such as bednets or indoor residual spraying are already widely used. Outdoor tools may therefore\r\ncomplement current indoor measures and improve control. We developed and evaluated a prototype mosquito\r\ncontrol device, the ââ?¬Ë?Mosquito Landing Boxââ?¬â?¢ (MLB), which is baited with human odours and treated with\r\nmosquitocidal agents. The findings are used to explore technical options and challenges relevant to luring and\r\nkilling outdoor-biting malaria vectors in endemic settings.\r\nMethods: Field experiments were conducted in Tanzania to assess if wild host-seeking mosquitoes 1) visited the\r\nMLBs, 2) stayed long or left shortly after arrival at the device, 3) visited the devices at times when humans were also\r\noutdoors, and 4) could be killed by contaminants applied on the devices. Odours suctioned from volunteer-occupied\r\ntents were also evaluated as a potential low-cost bait, by comparing baited and unbaited MLBs.\r\nResults: There were significantly more Anopheles arabiensis, An. funestus, Culex and Mansonia mosquitoes visiting\r\nbaited MLB than unbaited controls (P=0.028). Increasing sampling frequency from every 120 min to 60 and 30 min\r\nled to an increase in vector catches of up to 3.6 fold (P=0.002), indicating that many mosquitoes visited the device\r\nbut left shortly afterwards. Outdoor host-seeking activity of malaria vectors peaked between 7:30 and 10:30pm, and\r\nbetween 4:30 and 6:00am, matching durations when locals were also outdoors. Maximum mortality of mosquitoes\r\nvisiting MLBs sprayed or painted with formulations of candidate mosquitocidal agent (pirimiphos-methyl) was 51%.\r\nOdours from volunteer occupied tents attracted significantly more mosquitoes to MLBs than controls (P<0.001).\r\nConclusion: While odour-baited devices such as the MLBs clearly have potential against outdoor-biting mosquitoes\r\nin communities where LLINs are used, candidate contaminants must be those that are effective at ultra-low doses\r\neven after short contact periods, since important vector species such as An. arabiensis make only brief visits to such\r\ndevices. Natural human odours suctioned from occupied dwellings could constitute affordable sources of attractants\r\nto supplement odour baits for the devices. The killing agents used should be environmentally safe, long lasting, and\r\nhave different modes of action (other than pyrethroids as used on LLINs), to curb the risk of physiological insecticide\r\nresistance.
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