ARS | Publication request: Near-infrared spectroscopy as a complementary age grading and species identification tool for African malaria vectors

Submitted to: BioMed Central (BMC) Parasites and Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 4, 2010
Publication Date: June 4, 2010
Citation: Sikulu, M., Killeen, G.F., Hugo, L.E., Ryan, P.A., Dowell, K.M., Wirtz, R.A., Moore, S.J., Dowell, F.E. 2010. Near-infrared spectroscopy as a complementary age grading and species identification tool for African malaria vectors. BioMed Central (BMC) Parasites and Vectors. 3:49. Online. Parasites and Vectors doi: 10.1186/1756-3305-3-49.

Interpretive Summary: Mosquito survival is recognised as one of the imperative determinants of transmission for the pathogens they carry. For example, malaria vectors can only transmit malaria parasites when they are at least 10 days old because of the lengthy period required for Plasmodium parasite development in the mosquito. Traditionally, scientists relied upon labor-intensive and skilled techniques to assess disease transmission potential. We applied near-infrared spectroscopy (NIRS) to age-grade and differentiate mosquito species that transmit malaria. This method is simple, rapid (~1s), and non-destructive. We were able to classify mosquitoes as old or young with about 85% accuracy, and determine their species with about 90% accuracy. These findings have importance for monitoring control programs where reduction in the proportion of older mosquitoes of specific species that have the ability to transmit malaria is an important outcome.

Technical Abstract: Near-infrared spectroscopy (NIRS) was recently applied to age-grade and differentiate laboratory reared Anopheles gambiae sensu strico and Anopheles arabiensis sibling species of Anopheles gambiae sensu lato. In this study, we report further on the accuracy of this tool in simultaneously estimating the age class and differentiating the morphologically indistinguishable An. gambiae s.s. and An. arabiensis from semi-field releases and wild populations. Nine different ages (1, 3, 5, 7, 9, 11, 12, 14, 16 d) of An. arabiensis and eight different ages (1, 3, 5, 7, 9, 10, 11, 12 d) of An. gambiae s.s. maintained in 250 x 60 x 40 cm cages within a semi-field large-cage system and 105 female wild An. gambiae s.l., were included in this study. NIR classified female An. arabiensis and An. gambiae s.s. maintained in semi field cages as < 7 d old or = 7 d old with 89% (n=377) and 78 % (n=327) accuracy, respectively and differentiated them with 89% (n=704) accuracy. Wild caught An. gambiae s.l. were identified with 90% accuracy (n=105) whereas their predicted age were consistent with the expected mean chronological ages of the physiological age categories determined by dissections. These findings have importance for monitoring control programmes where reduction in the proportion of older mosquitoes that have the ability to transmit malaria is an important outcome.