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 species, it tends to infest healthy, intact ripe fruit, as opposed rotting or overripe fruit (Mitsui et al. 2006, Popul. Ecol. 48:233–237; Asplen 2015, J. Pest Sci. 88:469–494). drosophila adults are typically detected in the field using baited traps. This is useful helping growers decide when apply insecticides (Ebbenga 2022, Entomol. 57: 516–529), but methods also needed estimate actual infestation levels. Spectral imaging may provide nondestructive alternative extraction larvae could information on status single Such been tested for insect pests other than D. suzukii. For example, Peshlov (2009, Near Infrared Spectrosc. 17:203–212) used near-infrared spectroscopy (NIRS) detect wild blueberries (Vaccinium) by blueberry maggot, Rhagoletis mendax Curran Tephritidae). By measuring spectra live larva subtracting from an infested blueberry, they demonstrated that NIR signal recorded was “associated chemical changes blueberries.” Detectable differences between occurred approximately 750 1300 nm, with differential at 600 nm. Tsuta (2006, Food Technol. Res. 12:96–100) discriminate “foreign substances.” They measured various foreign substances, including worms, separately difference second derivative absorbance worms berries 625 675 nm.The F-750 Produce Quality Meter (Felix Instruments, Camas, WA) handheld visible spectrometer predict ripeness correlated constituents, such dry matter content cherry, Prunus avium L. (Toivonen 2017, Can. Plant 97:1030–1035). Light transmitted device's xenon tungsten lamp interacts scanned object then near zone illumination where recorded. The portability this device allows its use agricultural fields be beyond postharvest quality determination. Infestation levels eggs first instars undetectable human eye. If meter capable distinguishing uninfested would allow sorting culling small-acreage farmers who not have storage facilities cold enough arrest development (Aly Econ. Entom. 110:87–93). work conducted determine what extent can raspberries (Rubus).To test possibility suzukii, in-field assays artificial store-bought laboratory were initiated. samples, ‘Northblue’ ‘Chippewa’ (V. corymbosumL.ｘV. angustifoliumAit.) harvested Sand Plain Research Farm University Minnesota Becker, MN (45°23′36.42′’N, 93°52′36.3′’W). Berries collected weekly 5 26 July 2017 (100 week 1 50 each weeks 2, 3, 4), laboratory, placed 30-mL containers (Dart Container Corp., Mason, MI), one per container. incubated room temperature (21–23°C), fly emergence wk later.Artificial initiated laboratory. Blueberries purchased grocery store, disease, previous infestation, turgor loss discarded prior infestation. Scans compared poked pin (BioQuip Insect Pins, Black, #0, Bioquip Products, Rancho Dominguez, CA) simulate ovipositor injury without presence larvae. To individual two mated females 24 h clear plastic square filter paper absorb excess liquid. Adult flies removed after h, which all growth chamber 23–25°C, 16-h light:8-h dark photoperiod. Individual fruits 4 7 d Control treatments included (1) (2) infested.One-way blind tests 2021. Intact rinsed three times deionized water, air dried, dipped 2% (v/v) propionic acid (Fisher Scientific, Hampton, NH) s inhibit mold growth, entry sites. randomly assigned category R statistical software. Five female five male (to insure mating) flies, 3 old, added “infested” treatment No serving untreated controls. All kept light: 8-h After 36 removed, viewed under stereo microscope check egg breathing filaments. Containers delivered scanner did know contained Fruits 48, 72, 120 initial scored larval introduction adults.Each berry once Meter. pedicel-ends down light-emitting surface. A ring fabricated Delrin acetal homopolymer (DuPont, Wilmington, DE, USA) fit top 11-mm reflector cone improve support over central adapter provided manufacturer. Only machine-computed derivatives data collected. routine explained nine-point order Savitzky-Golay (Savitzky Golay 1964, Anal. Chem. 36:1627–1639).The accuracy rates one-way predictive according Hodgson (2004, 97:2127–2136). probability making correct determination across sets = Rpi (true positivesi+true negativesi), pi proportion n represented set i; true positivesi correctly identifying infestation; negativesi no Because there seven similar size (50–99 berries), 0.143.Field-harvested (Fig. 1A) showed patterns spectral harvest week. Mean 660- 690-nm range increased, decreased 692- 715-nm time. None harvests 2 Twenty percent 96% 42% 100% infested. Thus, mean greater less range. Similarly, artificially greater, whereas those 712-nm 1B). Although scans field-grown laboratory-infested suggested varied 53% 71%, error 29% 47% (data shown), positives 0.13, negatives 0.48 (Table 1). method better able (specificity) (precision recall).The inability study accurately positive infestations due decrease signal-to noise ratio about 980 However, obtained wavelengths 1000 nm discrimination blueberries. Also, improved analysis partial least squares modeling machine learning algorithms ability spectrometers suzuki berries.We thank Naxo Riera Vila Lucy DeBoer technical assistance, James Luby blueberries, Geoffrey Harms designing fabricating spectrometer. Funding College Food, Agriculture, Natural Resources Faculty Development Grant Experiment Station Project MN21-043.