HEALTH
in the population of mosquitoes, which start to bite people in the surrounding villages. The lack of infrastructure means that, when it rains, roads become impassable, and medics can’t get into villages to treat people.’ The product uses naturally
effectively tricking the mosquitoes into eating poison. The specific list of semiochemicals is confidential as the team awaits patents and licensing from the US Environmental Protection Agency, but the formulation includes terpenes, terpenoids and aromatic compounds. ‘The blend of chemicals that
we use to attract mosquitoes is so powerful that they will ignore natural plant odours and attractants, even ignoring nearby hosts in order to get to our formulation,’ says Mafra-Neto. ‘The product is so seductive that they will feed and engorge on it on it almost exclusively, even when it contains lethal doses of insecticide.’ Vectrax can be sprayed onto
vegetation or building eaves, or smeared as a gel into cracks in outdoor structures. According to Mafra-Neto, unpublished field tests in eight villages and 1000 houses in Tanzania showed that mosquito populations dropped by two-thirds in just two weeks in Vetrax-treated communities, compared with untreated ones. ‘In Tanzania, houses have holes
in between the walls and roof and mosquitos enter the house through those gaps,’ Mafra-Neto explains. ‘They come there looking for blood meals, but we hoped we could entice them into stopping first for a sweet meal. When we started seeing the nosedive in the mosquito population, down to zero in about six weeks, we were so happy. In one of the control village bedrooms, we caught over 300 mosquitos in one night.’
One problem with this treatment,
however, is that it still relies on an insecticide to deliver the final blow, even at very low doses. ‘All mosquitoes have the ability to develop resistance,’ says Willem
‘All mosquitoes have the ability to develop resistance. Even though in the short term it may kill mosquitoes, over time, the lure and kill strategy depending on insecticides will become ineffective’
Willem Takken Wageningen University, Netherlands 50%
Takken, a professor of public health entomology at Wageningen University, Netherlands. ‘Even though in the short term it
of mosquitoes can be diverted from humans to feed on goats using ‘Trojan cow’ -type technology.
Children infected with malaria parasites have a different odour composition that is more attractive to female mosquitoes. The children already produced these semiochemicals before becoming infected. However, the quantity of several compounds is significantly increased during infection, and after drug treatment, these compounds are reduced again.
may kill mosquitoes, over time, the lure and kill strategy depending on insecticides will become ineffective… In my view, a lure and kill strategy should be the combination of an attractant – the lure – and a biocontrol agent: entomopathogenic fungi, viruses, bacteria, nematodes etc. Insects do not rapidly resistance against natural enemies, and this strategy has thus the advantage to remain effective for a long time.’ Mafra-Neto’s second product,
however, uses a biological control strategy without help from a chemical pesticide. It aims to stop the population explosion of mosquitoes that occurs after heavy rain - by attracting and killing young mosquito larvae before they have the chance to grow into adults. ‘In Africa during the rainy season,
previously dry floodplains become flooded, and the puddles become ideal places for mosquitoes to lay their eggs,’ says Mafra-Neto. ‘You then get a huge explosion
occurring Bacillus thuringiensis israelensis (Bti) and Bacillus sphaericus (Bs) bacteria as a larvacide. The researchers incorporated the bacteria into the inner matrix of a commercially available biodegradable wax emulsion called SPLAT: Specialized Pheromone & Lure Application Technology. When used together the product is called SPLATbac. They then also inserted a special pheromone that attracts pregnant mosquitoes and encourages them to lay their eggs nearby. ‘A pregnant female mosquito
has to find the best puddle or other suitable water habitat to lay her eggs in so her larvae will turn into successful adult mosquitoes,’ says Mafra-Neto. ‘The eggs in puddles that are successfully developing release a specific odour in the air, 6-acetoxy-5-hexadecanolide, a semiochemical we call Mosquito Oviposition Pheromone.’ It is the release of this semiochemical that then attracts hundreds of other females to the same puddle, he continues. Pellets of the SPLATbac wax emulsions are applied to dry floodplains before the rainy season begins. They stick to vegetation, gravel and rocks before floating to the water surface when the rain arrives, slowly releasing the pheromone that attracts pregnant mosquitoes to lay their eggs in the treated water. On hatching, the mosquito larvae eat the bacteria and are killed, leaving non-target species, such as honey bees, unharmed. In a recent study, ISCA reports that a single 20mg pellet of a 10:1 dilution of SPLATbac in a larval tray containing 1L of water killed 100% of the larvae after five weeks1
.
The researchers now aim to conduct field trials in Tanzania, Côte d’Ivoire and in Brazil. Mafra-Neto’s third treatment,
‘Trojan Cow’, meanwhile, works by tricking mosquitoes that normally feed exclusively on humans into feeding on cows instead. The
28 10 | 2017
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