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Interactions gènes-environnement chez les moustiques et leur impact sur la résistance aux insecticides

Abstract : Mosquitoes have a major impact on public health due to their capacity to transmit human diseases such as viruses (dengue, yellow-fever, west-Nile, chikungunya…) and parasites (malaria, filariasis…). To control them, insecticides have been heavily used since the 1950's leading to the emergence of insecticide resistance. Today, wetlands where mosquito larvae develop are frequently contaminated by environmental xenobiotics (e.g. residual insecticides, agrochemicals, pollutants and plant allelochemicals) and little is known about the impact of these molecules on the capacity of mosquitoes to resist insecticides. The aim of my thesis is to study the response of mosquito larvae to xenobiotic exposures and the impact of these molecules on the tolerance (single generation) and resistance (multiple generations) of mosquitoes to chemical insecticides. A first ‘short term' study revealed that mosquito larvae exposed for few hours to sub-lethal doses of various xenobiotics become more tolerant to several chemical insecticides (Poupardin et al., 2008, Riaz et al., 2009) and that this increased tolerance is linked with an increase of detoxification enzyme activities. Thanks to the “Aedes detox chip” developed in LSTM, we showed that several detoxification genes, especially P450s, were induced by various xenobiotics which could explain the increased tolerance of mosquito larvae to insecticides. In order to better characterize these genes, their transcription profiles were studied at different life stages and in various organs (Poupardin et al., 2010). We demonstrated that several of these P450s are preferentially transcribed in gastric caeca, midgut and malpighian tubules, known to play an important role in xenobiotic metabolism. Moreover, we found that the transcription levels of these genes vary according to life stages. Finally, several genes were induced by environmental doses of xenobiotics with a maximum induction peak at 48-72h after exposure. Overall, these studies evidenced of the potential role of mosquito detoxification genes to respond to xenobiotic exposure and to affect their tolerance to chemical insecticides. The other aim of my thesis was to understand the ‘long term' (across several generations) impact of xenobiotics on the selection of insecticide resistance mechanisms in mosquitoes. In other words, ‘Do pollutants affect the selection of insecticides resistance mechanism by insecticides treatments' and if yes, ‘are particular genes favoured?' To answer these questions, three strains of the mosquito Aedes aegypti were selected with the pyrethroid insecticide permethrin. Before the selection process, larvae were exposed or not to sub-lethal dose of various pollutants. After 11 generations of selection, the three strains showed elevated resistance to permethrin compared to the susceptible strain. To identify the genes differentially transcribed in these resistant strains, we used the new ‘Agilent Aedes chip' representing more than 14,200 transcripts developed by the LSTM. Microarray results showed that the presence pollutants or residual insecticide can affect the selection of insecticide resistance mechanisms by favouring the selection of particular genes such as those encoding for detoxification enzymes (Poupardin et al., in prep). Globally, this research work will provide a better understanding of the impact of environmental factors on insecticide resistances in mosquitoes and will provide new ways to optimize the control of vectors with insecticides.
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Submitted on : Tuesday, April 5, 2011 - 4:24:07 PM
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Rodolphe Poupardin. Interactions gènes-environnement chez les moustiques et leur impact sur la résistance aux insecticides. Biodiversité. Université de Grenoble, 2011. Français. ⟨NNT : 2011GRENV005⟩. ⟨tel-00583441⟩

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