Implications of Sublethal Insecticide Exposure and the Development of Resistance on Mosquito Physiology, Behavior, and Pathogen Transmission

Abstract

For many decades, insecticides have been used to control mosquito populations in their larval and adult stages. Although changes in the population genetics, physiology, and behavior of mosquitoes exposed to lethal and sublethal doses of insecticides are expected, the relationships between these changes and their abilities to transmit pathogens remain unclear. Thus, we conducted a comprehensive review on the sublethal effects of insecticides and their contributions to insecticide resistance in mosquitoes, with the main focus on pyrethroids. We discuss the direct and acute effects of sublethal concentrations on individuals and populations, the changes in population genetics caused by the selection for resistance after insecticide exposure, and the major mechanisms underlying such resistance. Sublethal exposures negatively impact the individual's performance by affecting their physiology and behavior and leaving them at a disadvantage when compared to unexposed organisms. How these sublethal effects could change mosquito population sizes and diversity so that pathogen transmission risks can be affected is less clear. Furthermore, despite the beneficial and acute aspects of lethality, exposure to higher insecticide concentrations clearly impacts the population genetics by selecting resistant individuals, which may bring further and complex interactions for mosquitoes, vertebrate hosts, and pathogens. Finally, we raise several hypotheses concerning how the here revised impacts of insecticides on mosquitoes could interplay with vector-mediated pathogens' transmission.

Keywords: host-seeking behavior; insecticide exposure; insecticide resistance; mosquito; pathogen transmission.

Figure 1

Summary of potential impacts of different insecticide concentrations on mosquito physiology and behavior.

Figure 2

Time-related foraging behavioral changes potentially reducing the efficacy of Anopheles control. The colored lines within the clock represent the distribution of An. arabiensis biting times in places with short- (blue) or long-term (red) use of indoor residual sprays (IRS). The biting number decreases toward the center of the clock and increases toward the distal region of the clock. The clock indicates only the late afternoon and nighttime evaluation period from 6:30 p.m. (18:30) to 5:30 a.m. (5:30), as no data for other periods of the day were available. Adapted from Dukeen [158] and Yohannes [149].

Figure 3

Malaria transmission model predictions as impacted by insecticide resistance after the use of LLIN and IRS. LLIN: long-lasting insecticidal nets. IRS: indoors residual spray. EIR: entomological inoculation rate (infectious bites per person). Adapted from Gatton et al. [6].