Towards scalable age-grading of Aedes albopictus mosquito using mid-infrared spectroscopy and machine learning

Abstract

Abstract The age structure and dynamics of mosquito populations are crucial for understanding their ability to spread diseases and assessing the effectiveness of anti-mosquito control measures. However, available methods to age-grade mosquito populations are labour-intensive and imprecise, particularly for Aedes species. We investigated the potential of Mid-Infrared Spectroscopy (MIRS) combined with Supervised Machine Learning (ML) to rapidly and accurately predict the age of adult females and males of the arbovirus vector, Aedes albopictus . First, we demonstrated the ability of MIRS-ML to age male and female mosquitoes reared under laboratory conditions. Second, we optimised the model with adults emerged from wild collected eggs reared under natural conditions in a semi-field facility, to expose them to more realistic ambient conditions. For each sex we developed three ML models based on the resolution of the predicted adult age class: low (grouping of the mosquitoes by age in 9-day interval), medium (6 days) and high resolution (3 days) from 1 to 15 or 33 days for males and females, respectively. The prediction accuracy decreased as the resolution increased. In males, the accuracy dropped from 99% (low resolution model) to 93% (medium resolution model) and 85.8% (high resolution model); in females the low and medium resolution models showed 89.4% and 78.5% accuracy, which decreased to 72.6% for the high resolution. In a simulated vector control intervention, the high-resolution models allowed to detect shifts in the age-structure of Ae. Albopictus populations with minimal sampling effort (< 100 specimens). Finally, we validated MIRS-ML on two unseen data and reconstructed plausible age structures in (1) laboratory-reared and (2) field-collected Ae. albopictus males and females. Overall, the results represent a first step towards the development of a sound and reproducible MIRS-ML approach for age-grading of Ae. albopictus populations in the wild.