Crop edge sampling and early life stage detection for improved monitoring of spotted-wing drosophila, <i>Drosophila suzukii</i> (Diptera: Drosophilidae), in berry crops

In the 16 years since the initial detection of Drosophila suzukii Matsumura in the continental United States, integrated pest management programs in susceptible crops have been disrupted, resulting in unsustainable increases in insecticide sprays. Effective monitoring is critical for informing treatment decisions and to guide product selection when this pest is present. However, adult traps are difficult to process and poorly correlate with larval infestation in fruit. Recently focus has been placed on larval monitoring to document whether fruit are uninfested, starting to become infested, or heavily infested. We compared fruit sampling data from 4 states to determine whether these provide D. suzukii monitoring information which could better aid management decisions. We collected samples weekly for 6 wk at field edges and field interiors of berry crop plantings in Georgia, North Carolina, Michigan, and Oregon. Monitoring eggs and first instar larvae at field edges provided detection 2 wk earlier than monitoring later life stages or in field interiors. Here, we provide the first predictive models for the relationship between eggs and larvae in blackberries and blueberries. Our power analysis estimated that a minimum of 13 samples, either of individual fruit for egg counts or of 30 to 50 berry samples for larval extraction, are needed per location to detect the initial egg and larval infestation with 80% precision. These findings provide growers and other decision-makers with improved D. suzukii detection sensitivity, likely resulting in reduced pesticide application frequency and enhanced integrated pest management programs for berry crops producers.