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Non-destructive Determination of Age and Species of Anopheles gambiae s.l. Using Near-infrared Spectroscopy

Determining malaria vector species and age is crucial to measure malaria risk. Although different in ecology and susceptibility to control, the African malaria vectors Anopheles gambiae sensu stricto and An. arabiensis are morphologically similar and can be differentiated only by molecular techniques. Furthermore, few reliable methods exist to estimate the age of these vectors, which is a key predictor of malaria transmission intensity. We evaluated the use of near-infrared spectroscopy (NIRS) to determine vector species and age. This non-destructive technique predicted the species of field-collected mosquitoes with approximately 80% accuracy and predicted the species of laboratory-reared insects with almost 100% accuracy. The relative age of young or old females was predicted with approximately 80% accuracy, and young and old insects were predicted with 90% accuracy. For applications where rapid assessment of the age structure and species composition of wild vector populations is needed, NIRS offers a valuable alternative to traditional methods.

Received April 14, 2009. Accepted for publication July 6, 2009.

Acknowledgments: We thank Dr. Leon Hugo (Public Health Entomologist, Mosquito Control Laboratory, Queensland Institute of Medical Research, Herston, Queensland, Australia) and Dr. Benjamin Aldrich (Department of Anesthesia, University of Iowa, Iowa City, Iowa) for comments on early versions of this manuscript; Paul Howell (Malaria Research and Reference Reagent Resource Center, CDC) for providing mosquitoes; the International Atomic Energy Agency for providing fellowship funding to train Valeliana Mayagaya on the NIRS technique; Kristina Wyatt, Heather Wilkins, and Kjersti Kjos for rearing mosquitoes at KSU; the Biotechnology and Biological Sciences Research Council for providing funding for field collections in Tanzania; the Wellcome Trust for supporting the contribution of Gerry F. Killeen through Research Career Development Fellowship number 076806; Elizabeth Maghirang for help in scanning mosquitoes and analyzing data; and the CDC for providing travel funds for field tests.

^* Address correspondence to Floyd E. Dowell, Grain Marketing and Production Research Center, U.S. Department of Agriculture Agricultural Research Service, 1515 College Avenue, Manhattan KS 66502. E-mail: floyd.dowell{at}ars.usda.gov

Authors’ addresses: Valeliana Mayagaya, Ifakara Health Institute, Entomology Unit, PO Box 53, Ifakara, Tanzania, E-mail: vmayagaya{at}ihi.or.tz. Kristin Michel, Division of Biology, Kansas State University, 267 Chalmers Hall, Manhattan, KS 66506-4901, E-mail: kmichel{at}ksu.edu. Mark Q. Benedict, International Atomic Energy Agency Laboratories/Division of Human Health, A-2444, Seibersdorf, Austria, E-mail: m.benedict{at}iaea.org. Gerry F. Killeen, Ifakara Health Institute, Coordination Office, PO Box 78373, Kiko Avenue, Mikocheni B, Dar es Salaam, Tanzania, and Vector Group, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, United Kingdom, E-mail: gkilleen{at}ihi.or.tz. Robert A. Wirtz, Entomology Branch, Centers for Disease Control and Prevention, Mailstop F42, Atlanta, GA 30341-3724, E-mail: rwirtz{at}cdc.gov. Heather M. Ferguson, Institute of Biomedical and Life Sciences, University of Glasgow, 120 University Place, Glasgow, United Kingdom G12 8TA, E-mail: hferg001{at}udcf.gla.ac.uk. Floyd E. Dowell, Engineering and Wind Erosion Research Unit, Grain Marketing and Production Research Center, U.S. Department of Agriculture Agricultural Research Service, 1515 College Avenue, Manhattan, KS 66502, E-mail: floyd.dowell{at}ars.usda.gov.

Reprint requests: Floyd E. Dowell, Engineering and Wind Erosion Research Unit, Grain Marketing and Production Research Center, U.S. Department of Agriculture Agricultural Research Service, 1515 College Avenue, Manhattan, KS 66502, E-mail: floyd.dowell{at}ars.usda.gov.