Assessing the Effects of Trimethoprim on the Life History Traits of Anopheles stephensi

Background/Objectives: Malaria remains a major global health burden, particularly in sub-Saharan Africa, where the recent invasion and urban expansion of Anopheles stephensi are increasing transmission risk in densely populated areas. Conventional vector control strategies, including widespread insecticide application, are progressively losing efficacy due to the rapid spread of resistance. These limitations have accelerated the development of genetic control approaches aimed at either suppressing vector populations or replacing them with genetically modified mosquitoes incapable of transmitting pathogens, with the shared objective of reducing disease transmission. For population suppression strategies, an essential component is a conditional regulatory system that enables precise control of toxic or otherwise deleterious effector proteins. The most widely used platform, the tetracycline-dependent (Tet) system, modulates gene expression in response to tetracycline. However, this system can exhibit leaky expression and variable regulation, which may compromise its reliability and limit its application in certain contexts. The dihydrofolate reductase (DHFR) destabilization domain (DD) system, developed in Drosophila, offers an alternative strategy for post-translational control of protein stability. In this system, proteins fused to a destabilization domain are rapidly degraded unless stabilized by the small molecule trimethoprim (TMP), enabling tight and reversible control. In Drosophila and prior reports, this system has been associated with relatively low fitness costs, although such effects have not been systematically evaluated in mosquitoes. Before adapting this system for mosquito genetic control, it is therefore essential to assess the impact of TMP exposure on key life-history traits. Methods: Here, we assessed the effects of varying TMP concentrations on mosquito development, survival, and reproductive output. Results: Our results demonstrate that low concentrations of TMP exposure had no detectable effects on immature development, adult survival, or reproductive output under the conditions tested, supporting the implementation of the DHFR-DD system in mosquitoes. Importantly, these effects were dose-dependent, with moderate to high TMP concentrations producing measurable impacts on mosquito fitness. Conclusions: These findings provide a foundational step toward the development of more precise and reliable conditional expression systems for genetic vector control, advancing innovative strategies to mitigate malaria transmission in high-risk regions.