A rapid and non-destructive method to discriminate irradiated Ceratitis capitata (Diptera: Tephritidae) using near-infrared spectroscopy.

The sterile insect technique is a strategy to eradicate exotic pest outbreaks by releasing irradiated sterile insects to mate with wild insects, thus interfering with reproduction and leading to population decline. In fruit fly SIT programs, irradiated pupae are mixed with a fluorescent marker dye that transfers to the adults upon emergence from the pupal casing. The dye marker allows differentiation of sterile and wild flies caught in traps, which are used to monitor population outbreaks. Near-infrared (NIR) spectroscopy was evaluated as a rapid, non-destructive alternative to dyes to differentiate irradiated from wild-type medfly phenotypes. NIR spectrum (900 nm to 2,500 nm) of 1,212 irradiated and 1,061 non-irradiated mass-reared Vienna 7 strain Mediterranean fruit flies (medfly) males was processed and analyzed using machine learning methods to develop classifiers to discriminate between the irradiated and non-irradiated flies. A total classification rate (ie overall accuracy) of 84.2% for classifying irradiated and non-irradiated medflies was achieved using 11-point Savitzky-Golay 2nd derivatives. Total classification rates were 78.3%, 92.8%, and 88.6% for flies that were 1-to-6, 7-to-16, and >17 d old, respectively. These results demonstrate that the irradiated medfly phenotype can be differentiated from wild-type flies with relatively high accuracy. Further refinement of this technique for medfly and other tephritid fruit fly species using NIR hyperspectral imagers may be a valuable tool for ongoing SIT programs.