Abstract
Insecticide resistance threatens the success achieved through vector control in reducing the burden of malaria. An understanding of insecticide resistance mechanisms would help to develop novel tools and strategies to restore the efficacy of insecticides. Although we have substantially improved our understanding of the genetic basis of insecticide resistance over the last decade, we still know little of how environmental variations influence the mosquito phenotype. Here, we measured how variations in larval rearing conditions change the insecticide susceptibility phenotype of adult Anopheles mosquitoes. Anopheles gambiae and A. stephensi larvae were bred under different combinations of temperature, population density and nutrition, and the emerging adults were exposed to permethrin. Mosquitoes bred under different conditions showed considerable changes in mortality rates and body weight, with nutrition being the major factor. Weight is a strong predictor of insecticide susceptibility and bigger mosquitoes are more likely to survive insecticide treatment. The changes can be substantial, such that the same mosquito colony may be considered fully susceptible or highly resistant when judged by World Health Organization discriminatory concentrations. The results shown here emphasise the importance of the environmental background in developing insecticide resistance phenotypes, and caution for the interpretation of data generated by insecticide susceptibility assays.
Highlights
Insecticide resistance in mosquitoes, especially in malaria endemic regions, has increased dramatically in the last decade[1, 2]
This study investigated the influence of temperature, nutrition and crowding during the larval stage and adult body weight on the susceptibility of Anopheles gambiae KISUMU1 and A. stephensi STI adults to insecticides
Larvae growing at lower levels of population density and temperature were found to be protective for the adults, in both the KISUMU1 and the STI models
Summary
Insecticide resistance in mosquitoes, especially in malaria endemic regions, has increased dramatically in the last decade[1, 2]. Attempts to reduce the likelihood of the development of resistance to insecticide as well as to improve the success rates of interventions against disease vectors have led to the promotion of an integrated approach to the control of vector-borne diseases[4]. These combined interventions have been shown to be effective in significantly reducing malaria morbidity and mortality[5]. The responses of the larval stage to varying conditions could play an important role in population size regulation, and understanding these responses will contribute significantly to effective control measures. The implications of the observed effects for insecticide resistance monitoring are discussed
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