First report using near-infrared spectroscopy to age-grade Phlebotomus papatasi [Scopoli, 1786] sand flies

Vector age and survival directly influence vectorial capacity and disease transmission potential. Current age-grading techniques for phlebotomine sand flies are time-intensive and destructive as they require dissection by highly skilled laboratory personnel that groups hematophagous females as young or old depending on parity status. This study examined the potential of near-infrared spectroscopy (NIRS) to age-grade Phlebotomus papatasi sand flies, a primary vector of Leishmania major, a causative agent of cutaneous leishmaniasis. Female (n = 746) and male (n = 497) adult P. papatasi were collected 7, 14, and 21 days post-emergence. The NIR spectra from individual sand flies were used to develop a partial least squares regression model using a leave one out cross-validation approach. Independent test sets of P. papatasi were used to test the model prediction accuracy. When categorized as < 7 or ≥ 7 days old, the overall predictive accuracy was 85% for females and 87% for males. Sand flies reared in slightly cooler insectary conditions were also predicted with greater than 80% accuracy on average. For the first time, this study validates the use of NIRS as a non-destructive and rapid age-grading technique for P. papatasi.