Rapid and non-destructive method to discriminate irradiated Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann) for sterile insect release programs using near-infrared spectroscopy

The Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann) (Diptera: Tephrtidae), is a major cosmopolitan pest presenting significant threats to US agriculture. Among the most effective methods for control involves the use of sterile insect technique (SIT) where population establishment of medfly is prevented. For medfly SIT, mass-reared pupae are mixed with a fluorescent pink or orange external marker dye that will transfer to the adults upon emergence from the pupal casing. The dye, which fluoresces when exposed to ultraviolet light, is used to identify the flies as sterile, differentiating them from wild flies. This marking procedure, while effective, has some disadvantages, including that the dyes can be prone to error. In this study, we evaluated the feasibility of using near-infrared (NIR) spectroscopy to discriminate mass-reared irradiated flies from non-irradiated flies. NIR spectroscopy is a well-established technique for rapid and non-destructive analysis of chemical and physical properties in various industries as well as some entomological applications. Full NIR spectrum (900 nm to 2500 nm) of 2,273 mass-reared Vienna 7 medflies from the California Department of Food and Agriculture facility in Hawaii were measured using a benchtop spectrometer coupled with a backscatter optical fiber probe. The data was processed and analyzed using classical machine learning methods and algorithms were developed to discriminate between the irradiated and non-irradiated flies. A total classification rate (i.e. overall accuracy) of 78.9% was achieved with 11-point Savitzky-Golay 2nd derivatives pretreated spectra and a classification rate of 90.6% was achieved using a subset of 17-day and older flies.