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  • Publication
    Accès libre
    Effects of sublethal doses of an insecticide on the vectorial capacity of the malaria vector Anopheles gambiae
    (Neuchâtel, 2019)
    The presence of insecticide residues in water can strongly affect the development and life-history of mosquitoes. As the toxicity usually decreases along with the concentration, it is often considered that sub-lethal doses of insecticides induce negligible effects. However, there is increasing evidence that when applied at low doses, toxic substances may induce substantial and unpredictable effects on the organisms. Since these effects may affect the ability of mosquitoes to transmit pathogens, the study of sublethal doses in the context of vector ecology is of both an eco-toxicological and an epidemiological interest. In this thesis, the malaria mosquito vector and a pyrethroid insecticide were used to experimentally assess the consequences of low doses of insecticides on several aspects of mosquito’s vectorial capacity. In the different experiments, mosquitoes were mainly – but not only – exposed at larval stage to test for possible carry-over effects on the adults. In the first four chapters, the effect of the insecticide on mosquito’s development and adult life-history traits (Chap. 2), competence for the malaria parasite (Chap. 3), immunity (Chap. 4), and oxidative state (Chap. 5) were examined. In the sixth chapter, the possibility and consequences for mosquitoes to bite through an insecticide-treated bed-net (ITN) were explored. Finally, an evolutionary approach was used to test the possibility for both the insecticide at sublethal dose and the contact with an ITN to contribute to the evolution insecticide resistance (Chap. 7). As the response of mosquitoes to the insecticide may vary following environmental conditions, the effect of larval competition was additionally assessed as a proxy for limited resources. The results and their implications for both malaria transmission and the evolution of insecticide resistance are discussed throughout the thesis. Overall, this work provides a broader understanding of the physiological, epidemiological, and evolutionary consequences of the exposure of mosquito larvae to insecticide residues, and stresses the need for a better consideration of sub-lethal doses in the field of vector-borne diseases.