# Sublethal Pyriproxyfen Exposure Alters Anopheles arabiensis Fitness and Pyrethroid Susceptibility Without Trans-Generational Carry-Over

## TL;DR

Exposing mosquitoes to low doses of pyriproxyfen reduces their insecticide susceptibility and fitness without passing effects to future generations.

## Contribution

Sublethal pyriproxyfen exposure temporarily increases insecticide resistance and reduces mosquito fitness without trans-generational effects.

## Key findings

- Mosquitoes exposed to pyriproxyfen showed reduced susceptibility to permethrin and deltamethrin in the first generation.
- Exposure caused reduced fecundity, fertility, and smaller body size in the first generation.
- No trans-generational effects were observed in subsequent generations.

## Abstract

Malaria is spread by mosquitoes and controlling their population is an important way to reduce the disease. Scientists are testing new tools to help fight mosquitoes, especially as they become resistant to commonly used insecticides. One such tool is a chemical called pyriproxyfen, which works by interfering with mosquito development and reproduction. In this study, we exposed mosquito larvae to very small amounts of pyriproxyfen and observed the effects over three generations. We found that mosquitoes exposed to this chemical became temporarily tolerant to insecticides, but this effect is not transmissible to the next generation. We also saw that the exposed mosquitoes laid fewer eggs, had lower egg hatching rates, and were smaller in size. These results show that pyriproxyfen may be useful in mosquito control programs because it weakens mosquitoes without causing trans-generational carry-over. This approach could help improve the effectiveness of existing malaria control strategies and protect public health.

Background: Pyriproxyfen (PPF), a juvenile hormone analog, is a promising chemical for autodissemination strategies, where mosquitoes aid in transferring insecticides to their breeding sites. This study evaluated the effects of sublethal PPF doses 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 > 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). Conclusions: 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.