Seasonal phenology and host plant use by Leptopilina japonica (Hymenoptera: Figitidae) attacking Drosophila (Diptera: Drosophilidae) in managed and unmanaged habitats, determined using a modified sticky trap collection method.

Biological control of Drosophila suzukii may be enhanced through adventive populations of the figitid parasitoid Leptopilina japonica (Novković & Kimura) (Hymenoptera: Figitidae). This insect has expanded its range considerably but we have limited understanding of the phenology, wild host plant associations, and response to fruit crop management of this parasitoid. To address these gaps, fruit samples were collected in wild and managed habitats across southern Michigan, placed on metal mesh in a plastic container until insects emerged, when they were captured and identified. We selected yellow sticky traps based on experiments to compare trap types for capture of D. suzukii and L. japonica. Weekly checking of traps resulted in 2,108 samples across 2022 and 2023 yielding 7,598 Leptopilina japonica specimens. Wasp detection started in mid-July and increased steadily until mid-September, with activity declining into October. Leptopilina japonica emerged from multiple plant species, with the highest yield in both years from blackberry (Rubus spp.), American black elderberry (Sambucus canadensis), and pokeweed (Phytolacca americana) fruit. Leptopilina japonica was much more abundant in unmanaged and organic blueberry plantings than in commercial fields during berry ripening, with a sharp increase in commercial fields after pesticide applications ended. The methods described here facilitate widespread sampling for Drosophila parasitoids without needing daily collection of emerged insects. Our results highlight an updated sampling method showing that L. japonica has established in the berry production regions of Michigan, persisting on Drosophila (Diptera: Drosophilidae) larvae in berries of wild and managed host plants that ripen through the growing season.