Sampling Methods and Distribution of Figitid Parasitoids of Drosophila suzukii in Washington State

Robert Czokajlo

Classical biological control is a control method favored for combatting invasive pests, which often arrive in the invaded range without their complement of predators and parasitoids. This method typically involves foreign exploration for natural enemies in the native range, establishing their efficacy, screening for impact on nontarget species, obtaining a permit for release, and rearing in sufficient quantities for releases. This method has been applied to a relatively recent invasive pest of the continental United States, spotted-wing drosophila (Drosophila suzukii Matsumura; Diptera: Drosophilidae). Two candidate parasitoids were identified in this process, Ganaspis kimorum Buffington and Leptopilina japonica Novković & Kimura (Hymenoptera: Figitidae). Concurrent with the issuing of a permit for one candidate parasitoid, G. kimorum, adventive populations of both species were found in Washington. I developed two studies to support biological control efforts for D. suzukii: 1) evaluating sampling methods for figitid parasitoids and 2) determining their distribution and phenology in Washington state. The sampling methods comparison was conducted in 2023-2024, and indicated that jar traps with either a wine-vinegar bait or an artificial lure with a drowning solution captured more figitids than the other methods tried (fruit sampling, fruit sentinels, and a yellow sticky card with an artificial lure). The liquid trap method appears to be most suitable for detection of low populations in surveys or post-release recovery, thus providing a more practical and effective alternative to the previous standard of berry collections. The survey, which focused on the principal fruit-growing districts east of the Cascade mountains, revealed that a third cosmopolitan figitid species, L. heterotoma (Thomson), was the most abundant parasitoid in this region. However, L. japonica was also widely distributed throughout the area. Ganaspis kimorum was not detected in eastern Washington but was found in a limited number of traps placed on the west side of the Cascades. These results provide a baseline for the distribution of these species and can be used for comparison with later assessments after releases of G. kimorum have been completed. It also supports the concept of augmentative releases of L. japonica, because its adventive establishment indicates that it can adapt to eastern Washington’s semi-arid climate.

Sampling Methods and Distribution of Figitid Parasitoids of Drosophila suzukii in Washington State

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