Pixel intensity of wing photos used to infer efficacy of mosquito control interventions against Anopheles gambiae caught during the RIMDAMAL II clinical trial

Mosquito age-grading is important for evaluating mosquito control efforts and estimating pathogen transmission risk. We previously developed a simple, low-cost, and high-throughput method to age-grade mosquitoes by computing the pixel intensity (PI) of wing photos, which reflects wing scale loss over time. Here the technique was refined and used to understand wild Anopheles gambiae population structures from the RIMDAMAL II clinical trial. PI distributions from wing photos of wild An. gambiae caught during the trial reflected wild population structures assessed by gold standard techniques, where most individuals clustered in the lower PI value ranges and there was a long thin distribution tail of fewer individuals with high PI values. The wild mosquitoes also had a wider PI range than those from colony An. gambiae reared to known ages in a laboratory mesocosm. Analyses from the RIMDAMAL II trial indicate that while ivermectin mass drug administrations in the intervention arm may have modestly influenced PI relative to controls, distributions of new dual-chemistry insecticide treated bed nets in both arms were associated with a strong effect on PI, as well as on predicted age structure generated from the laboratory-based age model. These data suggest this method can be used to rapidly infer the efficacy of vector control interventions and may accurately predict wild type mosquito age with future optimized age models.