Near-infrared spectroscopy discriminates mass-reared sterile and wild tsetse flies

Monitoring the efficacy of the sterile insect technique (SIT) programs, it is desirable to discriminate between wild and sterile tsetse males captured in monitoring traps. Currently, this is primarily achieved by marking sterile males with fluorescent dye powder before release, and identifying them using a fluorescence camera and/or microscope. However, the accuracy of this method is limited due to defective marking and wild flies contaminated with a few dye particles in the monitoring traps. Molecular techniques have been developed to discriminate doubtful flies, but they are expensive for endemic countries.

Here, we investigate the ability of a new generation monitoring tool, Near-Infrared Spectroscopy (NIRS), to discriminate between laboratory-reared Glossina palpalis gambiensis males and their field counterparts. NIRS was able to discriminate wild males from laboratory-reared males with 86% accuracy. Notably, the prediction accuracy improved to 88% when the laboratory-reared flies had been irradiated.

These findings suggest that NIRS can successfully identify tsetse flies even when UV camera identification is inconclusive. However, further studies are needed to expand the training dataset and include additional environmental variables before validating NIRS as a complementary method for future tsetse eradication programs.