Insecticide susceptibility of Anopheles mosquitoes changes in response to variations in the larval environment

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.

Evidence for family-level variation of phenotypic traits in response to temperature of Brazilian Nyssorhynchus darlingi

“…Vector control interventions need to consider variation in life history traits [7], behaviors [5], and habitats [21]. At a high nutrition diet, low temperature treatment Anopheles were found to be larger and more likely to survive exposure to a LC 50 dose of permethrin [60]. Data from our study suggest that larger doses of permethrin would be required in southern compared to northern populations of Ny.…”

Physical and Chemical Factors of Breeding Sites Affecting Susceptibility and Biochemical Activity of Mosquito, <i>Culex pipiens</i> (Diptera: Culicidae) to Some Insecticides

“…Aedes aegypti was unusual in their ability to survive and developed in waters ranging from pH•4 to 11. Also mosquitoes bred under different conditions showed considerable changes in mortality rates and body weight, with nutrition being the major factor, they also demonstrated that temperature, crowding and availability of nutrition during the larval stages directly or indirectly modulate 24 hours mortality in the adult when exposed to permethrin [26].…”

Evaluating insecticide resistance across African districts to aid malaria control decisions

“…Susceptibility test data are noisy ( 29 , 30 ) and the low data volumes typically seen in resistance monitoring ( Fig. 1 ) are particularly susceptible to issues of data noise.…”