Back to the Future: Quantifying Wing Wear as a Method to Measure Mosquito Age

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  • 1 Center for Vector-Borne Infectious Diseases, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado;
  • | 2 Viden Technologies LLC, Laramie, Wyoming;
  • | 3 MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Imperial College, London, United Kingdom
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Vector biologists have long sought the ability to accurately quantify the age of wild mosquito populations, a metric used to measure vector control efficiency. This has proven difficult due to the difficulties of working in the field and the biological complexities of wild mosquitoes. Ideal age grading techniques must overcome both challenges while also providing epidemiologically relevant age measurements. Given these requirements, the Detinova parity technique, which estimates age from the mosquito ovary and tracheole skein morphology, has been most often used for mosquito age grading despite significant limitations, including being based solely on the physiology of ovarian development. Here, we have developed a modernized version of the original mosquito aging method that evaluated wing wear, expanding it to estimate mosquito chronological age from wing scale loss. We conducted laboratory experiments using adult Anopheles gambiae held in insectary cages or mesocosms, the latter of which also featured ivermectin bloodmeal treatments to change the population age structure. Mosquitoes were age graded by parity assessments and both human- and computational-based wing evaluations. Although the Detinova technique was not able to detect differences in age population structure between treated and control mesocosms, significant differences were apparent using the wing scale technique. Analysis of wing images using averaged left- and right-wing pixel intensity scores predicted mosquito age at high accuracy (overall test accuracy: 83.4%, average training accuracy: 89.7%). This suggests that this technique could be an accurate and practical tool for mosquito age grading though further evaluation in wild mosquito populations is required.

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Author Notes

Address correspondence to Brian D. Foy, Center for Vector-Borne Infectious Diseases, Department of Microbiology, Immunology and Pathology, Colorado State University, 200 W Lake St., Fort Collins, CO 80521. E-mail: brian.foy@colostate.edu

Financial support: This project was supported by a research subagreement from the Innovative Vector Control Consortium. R. M. and T. S. C. were supported by the UK Medical Research Council (MRC) Project Grant (no. MR/P01111X/1) and the MRC Centre for Global Infectious Disease Analysis (reference MR/R015600/1), jointly funded by the UK Medical Research Council (MRC) and the UK Foreign, Commonwealth & Development Office (FCDO), under the MRC/FCDO Concordat agreement and is also part of the EDCTP2 programme supported by the European Union.

Authors’ addresses: Lyndsey Gray, Greg Pugh, Erin D. Markle, and Brian D. Foy, Center for Vector-Borne Infectious Diseases, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO, E-mails: ligray121288@gmail.com, greg.pugh@colostate.edu, erindanmarkle@gmail.com, and brian.foy@colostate.edu. Bryce C. Asay and Blue Hephaestus, Viden Technologies LLC, Laramie, WY, E-mails: bryce.viden@outlook.com and bluekroma@gmail.com. Ruth McCabe and Thomas S. Churcher, MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Imperial College, London, United Kingdom, E-mails: ruth.mccabe17@imperial.ac.uk and thomas.churcher@imperial.ac.uk.

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