Interactions between Drosophila suzukii, its parasitoid Ganaspis kimorum, and the environment

Biological control of Drosophila suzukii with Ganaspis kimorum, a specialist parasitoid, is believed to have high potential due to the high host specificity of G.kimorum and their capability to overcome D. suzukii’s immune response. Establishing populations of G. kimorum in the US, however, has not been as quick or successful as originally anticipated. One possible issue lies in the fact that G. kimorum appears to prefer parasitizing D. suzukii within fresh fruit, which often only occurs for short periods of time during the growing season. This study seeks to determine oviposition preference of both D. suzukii and G. kimorum for attached fruit vs. fruit that has dropped from the canopy, as well as investigating the impact of berry and soil temperature and parasitoid presence on successful D. suzukii emergence. Preliminary results from this study, conducted under semi-field conditions in blueberry fields during the summer of 2023, found that arenas where G. kimorum were present together with D. suzukii showed significantly lower levels of adult fly emergence during later rearing. Even though these trials did not result in successful D. suzukii parasitism as evidenced by adult G. kimorum emergence, the mere presence of parasitoids resulted in significantly lower levels of D. suzukii reared from the test arenas. Despite some differences in temperature being recorded between attached and fallen berries, no significant difference in adult fly emergence was found to be present between the two groups. Later work will build upon this foundation to further illuminate these relationships under more real-world conditions.