Facilitating mass rearing of a spotted wing drosophila parasitoid via cold storage

Spotted wing drosophila, Drosophila suzukii, is a major global pest of soft fruit that is invasive in the United States. Current biological control practices mainly rely on mass releases of native pupal parasitoids (e.g., Pachycrepoideus vindemiae) that require a large supply of parasitoids during the growing season. Optimizing rearing to provide enough parasitoids during crucial times we assessed the use of cold storage during three points in the production process of P. vindemiae: (1) host pupae prior to parasitization, (2) immature parasitoids and (3) adult parasitoids. For (1), D. melanogaster pupae of different ages (1, 2, 3 days old) were stored at different temperatures (+8°C, -20°C, -80°C) and exposed to P. vindemiae females after different storage durations (1, 7, 14, 30, 120 days). Parasitoid offspring emergence was highest from 2-day old pupae stored at -80°C and pupae could be stored for up to 4 months without significant decrease in parasitoid offspring emergence. Drosophila melanogaster pupae containing P. vindemiae eggs, larvae, or pre-pupae (2), and adult P. vindemiae (3) were stored at +8°C for different durations (1, 7, 30, 120 days) after which emergence (2) and fecundity (3) was measured to ascertain parasitoid fitness. The results of these experiments will enable insectaries to stockpile D. melanogaster as an alternative host to mass rear P. vindemiae for releases against D. suzukii and store P. vindemiae for peak production times.