Comparison of sampling methods for figitid parasitoid wasps of spotted-wing drosophila

The purpose of this study was to determine which of the proposed sampling methods proved most effective at capturing parasitoid wasps (Hymenoptera: Figitidae) of spotted-wing drosophila (Drosophila suzukii Matsumura). Focus was given to capturing two Asian species Ganaspis kimorum and Leptopilina japonica and the native Leptopilina heterotoma. Tracking the success of releases (of G. kimorum) and adventive establishment of L. japonica is important for measuring the success of biological control programs. Sampling was conducted at six different sites (50 m-long patch of wild Himalayan blackberry) in northwestern Washington state using five sampling methods: 1) fruit sampling (blackberries); 2) fruit sentinels (blueberries infested with the appropriate stage of D. suzukii); 3) a 1-liter jar trap with wine/vinegar bait, 4) a jar trap with a Scentry lure and drowning solution, and 5) a yellow sticky card with a Scentry SWD lure. Traps and/or samples were collected every other week from mid-June to late-October 2023, and again from mid-May to late-October 2024. Treatments were randomly rotated among five established positions in the patch at each visit. Figitid specimens were counted and identified to species; numbers of D. suzukii were also counted. More than 1200 figitids were captured, with numbers increasing sharply in early fall. Leptopilina japonica was the most abundant species captured, comprising 98% of all figitids found. The two jar trap methods caught >10-fold more figitids than the fruit samples and sticky cards, which yielded similar results to each other. Only fruit sentinels failed to capture any figitids.