Detection of Spotted-winged Drosophila (Diptera: Drosophilidae) Infestations in Blueberry Fruits1

Spotted-winged drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), has become a significant pest of small and stone fruit. Unlike most Drosophila species, it tends to infest healthy, intact ripe fruit, as opposed to rotting or overripe fruit (Mitsui et al. 2006, Popul. Ecol. 48:233–237; Asplen et al. 2015, J. Pest Sci. 88:469–494). Spotted-winged drosophila adults are typically detected in the field using baited traps. This is useful in helping growers decide when to apply insecticides (Ebbenga et al. 2022, J. Entomol. Sci. 57: 516–529), but methods are also needed to estimate actual fruit infestation levels. Spectral imaging of fruit may provide a nondestructive alternative to extraction of larvae and could provide information on the infestation status of a single fruit. Such imaging has been tested for insect pests other than D. suzukii. For example, Peshlov et al. (2009, J. Near Infrared Spectrosc. 17:203–212) used near-infrared spectroscopy (NIRS) to detect infestation of wild blueberries (Vaccinium) by blueberry maggot, Rhagoletis mendax Curran (Diptera: Tephritidae). By measuring spectra of a live larva and subtracting it from an infested blueberry, they demonstrated that the NIR signal they recorded was from a larva and ‘‘associated chemical changes in the blueberries.’’ Detectable differences between infested blueberry and larvae occurred between approximately 750 and 1300 nm, with a small differential signal at 600 nm. Tsuta et al. (2006, Food Sci. Technol. Res. 12:96–100) also used spectroscopy to discriminate between blueberry fruit and ‘‘foreign substances.’’ They measured the spectra of various foreign substances, including worms, separately from the fruit. They detected a difference in the second derivative of absorbance between worms and berries between approximately 625 and 675 nm.