Sublethal Pyriproxyfen Exposure Alters <em>Anopheles arabiensis</em> Fitness and Pyrethroid Susceptibility without Trans-Generational Carry-Over

Background: Pyriproxyfen (PPF), a juvenile hormone analogue is a promising chemistry for autodissemination strategies, where mosquitoes aid in transferring insecticides to their breeding sites. This study evaluated the effects of sublethal PPF exposure on Anopheles arabiensis fitness (fecundity, fertility, and body size) and pyrethroids susceptibility across three generations. Methods: Laboratory-reared, pyrethroid-resistant mosquito larvae were exposed once to sublethal PPF concentrations of (0.0003, 0.0006, 0.0008, and 0.001 mg a.i./L), which caused emergence inhibition rates of 5%, 10%, 15%, and 20%, respectively, alongside a control group. Emerged adults were tested for susceptibility to 0.75% permethrin, 3.75% permethrin and 0.05% deltamethrin using WHO tube bioassays. Knockdown was recorded at 1 h, mortality at 24 h post-exposure, while fecundity, fertility, and body size were measured across three generations. Results: First-generation Anopheles arabiensis emerging from PPF-treated larvae showed reduced susceptibility to 0.75% permethrin and 0.05% deltamethrin compared to controls. Mortality from permethrin dropped from 22.7% in the controls to 11% and then 3% at 0.0003 and 0.001 mg a.i./L. For deltamethrin, mortality fell from 62.7% to 36% and then 23.3% at the same concentrations. Knockdown at 60 min was also significantly reduced, with permethrin KDT₆₀ dropping from 41.3% in controls to 9.3% and 3.3%, and deltamethrin KDT₆₀ from 79.7% to 66.7% and 65%. No significant differences were observed in subsequent generations (p &gt; 0.05). PPF exposure also induced notable fitness costs in the first generation: mean wing length decreased from 3.07 mm in controls to 2.88–2.66 mm (6–13% reduction), mean egg production dropped from 30.1 to 13.9–18.8 eggs per female (37–54% reduction), and egg hatching rate declined from 87% to 79–82% (6–9% reduction). Conclusion: These findings suggest that sublethal PPF doses can temporarily enhance insecticide resistance without leading to heritable resistance and negatively impact key mosquito fitness traits. PPF may thus be a valuable addition to integrated vector management strategies.