Comparison of sampling methods for figitid parasitoids of Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii (Matsumura) is an invasive pest of berries and cherries in Washington State, and as a direct fruit feeder, has become a key pest in the affected crops. The recent interest in classical biological control using Asian parasitoids in the family Figitidae highlights the need for effective sampling methods. Whether adventively established or released by research labs, surveys and follow-up sampling for parasitoid detection is an important step in tracking their spread and ultimately, the success of release endeavors. In this study, we examined 5 proposed sampling approaches to determine their capture rates, relative effort, and ease of use. The study was conducted over 2 seasons in northwestern Washington State, where 2 Asian figitids, Ganaspis kimorum Buffington and Leptopilina japonica Novkovic & Kimura, were adventively established. Liquid-based D. suzukii traps using either wine-vinegar bait or an artificial lure captured ca. 10.6- to 256.6-fold more figitids than field collected fruit. However, liquid traps yielded mediocre specimens (for morphological identification or PCR analyses) and required considerable time to sort out the target species from by-catch. Yellow sticky cards with a synthetic lure had a similar capture rate as fruit sampling, but with poorer quality specimens. Fruit sampling yielded higher quality specimens and allowed for an association (including % parasitism) between host and parasitoid but was restricted to periods when ripe fruit was available. Deploying D. suzukii-infested fruit sentinels was labor intensive and captured only one adult figitid over 2 yr, suggesting that this was the least practical method.