Near-infrared spectroscopy, a rapid method for predicting the age of male and female wild-type and Wolbachia infected Aedes aegypti

Authors: SIKULU-LORD, MAGGY - Queensland Institute Of Medical Research; MASABHO, PETER - Ifakara Health Institute; HENRY, MICHAEL - Ifakara Health Institute; WIRTZ, ROBERT - Centers For Disease Control And Prevention (CDC) - United States; HUGO, LEON - Queensland Institute Of Medical Research; Dowell, Floyd; DEVINE, GREGOR - Queensland Institute Of Medical Research

Submitted to: PLOS Neglected Tropical Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2016
Publication Date: 10/21/2016
Publication URL: http://handle.nal.usda.gov/10113/5678121
Citation: Sikulu-Lord, M.T., Masabho, P.M., Henry, M., Wirtz, R.A., Hugo, L.E., Dowell, F.E., Devine, G.J. 2016. Near-infrared spectroscopy, a rapid method for predicting the age of male and female wild-type and Wolbachia infected Aedes aegypti. PLOS Neglected Tropical Diseases. 10(10):e0005040. doi:10.1371/journal.pntd.0005040.

Interpretive Summary: Aedes aegypti is the principal vector for dengue, chikungunya and Zika viruses. These viruses require a period of development inside the mosquito before they can be transmitted to humans. Depending on environmental factors, dengue and Zika viruses take 7-10 days to mature inside the mosquito whereas chikungunya virus takes 2-7 days to mature. The age of mosquitoes is therefore a critical determinant of disease transmission. A mosquito control strategy utilizing an endosymbiotic bacterium Wolbachia pipients has been proven effective at blocking dengue transmission in Ae. aegypti mosquitoes. To ensure their effective removal of potentially infectious mosquitoes, the efficacy of this and existing interventions must be routinely monitored using age grading techniques. In this study, we investigated the applicability of a rapid and cost effective near-infrared spectroscopy (NIRS) method for age grading wild type and Wolbachia infected Ae. aegypti mosquitoes. We report that NIRS can facilitate the differentiation of male and female Ae. aegypti into multiple age groups and demonstrate that it can quickly differentiate young from potentially infectious Ae. aegypti with an accuracy of up to 91%.

Technical Abstract: Estimating the age distribution of mosquito populations is crucial for assessing their capacity to transmit disease and for evaluating the efficacy of available vector control programs. This study reports on the capacity of near-infrared spectroscopy (NIRS) technique to rapidly predict the ages of the principal dengue and Zika vector Aedes aegypti. Wild type males and females and males and females transinfected with wMel and wMelPop strains of Wolbachia pipientis were investigated. Calibrations were developed using spectra collected from their heads and thoraces using partial least squares (PLS) regression. A highly significant correlation was found between the true and predicted ages of mosquitoes. The coefficient of determination for wild type females and males were R2 = 0.84 and 0.78 respectively. The coefficient of determination for wMel and wMelPop infected females were 0.71 and 0.80, respectively (P< 0.001 in both instances). The age of wild type female Ae. aegypti could be identified as < or = 8 days old with an accuracy of 91% (N=501), whereas female Ae. aegypti infected with wMel and wMelPop were differentiated into the two groups with an accuracy of 83% (N=284) and 78% (N=229), respectively. Our results also indicate NIRS can distinguish between young and old male wild type, wMel and wMelPop infected Ae. aegypti with accuracies of 87%, 83% and 78%, respectively. This is the first investigation that reports the potential of the NIRS technique as a rapid technique for identifying the age of Aedes aegypti mosquitoes.