Evaluating Real-Time PCR to Quantify Drosophila suzukii Infestation of Fruit Crops

Common methods for detecting Drosophila suzukii (spotted-wing drosophila, SWD) in fruit, such as microscopy, physical extraction, and incubation, are time-consuming and may underrepresent egg and first instar larvae counts, the smallest life stages of SWD. To address these limitations, we evaluated a quantitative real-time PCR (qPCR) protocol to detect and quantify SWD eggs using a linear model of the log-transformed ratio of eggs to sample volume (µL) in Tris buffer and fruit tissue. Compared to traditional approaches, this method reduces identification time from several weeks to approximately five hours. We observed a negative linear correlation between qPCR cycle threshold and egg concentration in both standard and fruit tissue samples, with similar model fits (R² = 0.7215 for field fruit tissue; R² = 0.874 for standard samples). This DNA-based protocol improves infestation detection speed and accuracy by enabling rapid, species-specific identification of D. suzukii in fruit tissue, addressing limitations of morphological identification of eggs and larvae. Further refinement for fruit tissue could enhance real-world applicability. Rapid detection may enable timely assessment of varietal resistance to SWD and support safer control strategies targeting early life stages, helping to prevent pest development and fruit degradation.