Life-History Trade-Offs in Pyrethroid-Resistant Culex quinquefasciatus: Rethinking Vector Control Paradigms

Culex quinquefasciatus, a primary vector of life-threatening and debilitating diseases, is subjected to persistent insecticidal selection pressure through vector control measures and potential exposure to run-offs from agrochemicals. This study investigated the fitness trade-offs linked to pyrethroid resistance in Culex quinquefasciatus. We selected Culex quinquefasciatus strains against 50% lethal concentration (LC₅₀) of alphacypermethrin (AS strain) and permethrin (PS strain) for 24 generations, followed by 12 generations without selection pressure. A susceptible strain (S strain) was maintained for 36 generations without exposure to pyrethroids. Life history traits, including fecundity, developmental time, and lifespan, were compared among strains. Pyrethroid-selected strains (AS and PS) exhibited reduced fecundity, prolonged developmental duration, and shortened lifespan relative to the susceptible strain. AS and PS strains showed elevated levels of monooxygenase activity and glutathione-S-transferase activity, while no significant changes in the level of esterases than that of the S strain. Moreover, the kdr mutation L1014F was fixed in both the AS and PS strains. These findings indicate that pyrethroid resistance incurs significant biological fitness costs in Culex quinquefasciatus. Exploiting the fitness trade-offs of pyrethroid-resistant mosquitoes through rotational use of insecticides with varied mechanisms may serve to decelerate resistance evolution.