HEALTH
UT MALARIA T
o find her ‘blood meal’, a female Anopheles mosquito relies on her acute sense of smell, which allows her to
pick out the intoxicating odours in human sweat – and even the carbon dioxide in our breath. For some unfortunate people, the
resulting skin prick may be deadly. Female Anopheles mosquitoes infected with the single-celled parasite Plasmodium can transmit the organism – responsible for malaria – to humans. Currently, the most effective
way of controlling mosquito populations is blanket spraying with pyrethoid insecticides, DDT, organophosphates and methoprene, and using insecticide coated protective mosquito nets. However, this approach exposes people and animals to potentially harmful chemicals, and can kill bees and other beneficial insects, while the sprays can also contaminate soils and streams. In recent years, mosquitoes have also begun developing resistance to pyrethroids and other insecticides. Now, several alternative
treatments are in development that exploit mosquitoes’ sense of smell in order to manipulate their behaviour. In his lab in California, Agenor Mafra-Neto of ISCA Technologies synthesises ‘semiochemicals’ – odorant compounds naturally produced by plants and other animals that influence insects’
contains a mix of sugars and proteins that mimic 20 common semiochemical signals used by plants to attract mosquitoes to nectar-producing flowers. These are blended with insecticides such as pyrethroids or spinosad,
behaviour. Pheromones emitted by insects help them find mates, food and habitat resources, for example, while plants also produce semiochemicals to attract insects. At the American Chemical Society’s annual conference in Washington DC in spring 2017, Mafra-Neto announced three separate treatments that could kill mosquitoes and reduce the transmission of malaria. The first takes advantage of mosquitoes’ sweet tooth - they don’t just drink blood, they also need sugar to survive. Plants naturally produce sweet smelling aroma compounds to attract the mosquitoes. Mafra-Neto’s group took extracts from flowers and other plants that produce nectar, and then used gas chromatography electroantennographic detection to separate and identify the sweet smelling and tasting compounds. They then tested which of these thousands of compounds were most attractive to mosquitoes by exposing their antennae to them and looking for a neurological response. They did the same with bees, allowing them to screen out aroma components that would also attract them. The resulting product, Vectrax,
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