Pixel intensity of wing photos used to predict age of Anopheles gambiae caught during the RIMDAMAL II clinical trial

Abstract

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. Wing photos from lab-reared An. gambiae had narrower PI ranges compared to wild An. gambiae s.l., but the PI distributions reflected wild population structures where most have lower PI values and very few high PI values. A model was then fitted to samples from lab mosquitoes of known ages and used to interpolate unknown ages from the wild populations (median age of 4.96 [0.8-14.93] days old). Analyses from the RIMDAMAL II trial indicate that while ivermectin mass drug administrations in the intervention arm may have modestly influenced PI and predicted age relative to controls, distributions of new dual-chemistry bed nets in both arms were associated with a strong effect on PI and predicted age structure. These data suggest this method can be used to rapidly age-grade wild mosquito populations and infer the efficacy of vector control interventions.