Improving spotted-wing drosophila monitoring using adult captures to estimate larval infestation risk

Spotted wing drosophila (SWD), Drosophila suzukii, is an invasive pest of soft-skinned fruit and has caused significant economic losses worldwide. Growers often rely on calendar-based sprays to manage SWD, and the cost of chemical inputs and labor has increased annually. Incorporating pest monitoring into a management strategy could improve efficiency and reduce the number of pesticide sprays. The objective of this study was to establish a relationship between adult male captures in traps and larval infestation as a basis for improving decision making. We conducted this study across four conventional blueberry farms in New York in 2022 and three organic or low-spray blueberry sites in 2023. We deployed 10 red sticky traps baited with broad-spectrum lures per site and recorded the number of SWD males caught on both sides of the traps weekly. We used the salt extraction method to assess the infestation of fruits, where we collected 25 to 30 ripe berries from within one meter of each red sticky trap. Our data showed that male SWD were captured on cards one to two weeks before larvae were found in fruit samples. In addition, we observed a positive correlation between male adult capture and larval infestation in most sites in both years. Although adult trap data can be useful in early warning signals for fruit infestation, developing action thresholds and making management decisions based on adult trap counts remains challenging for an invasive pest with very low tolerance for larval infestation.