Prospects and constraints in the implementation of Drosophila suzukii classical biological control in Italy four years after the first release

Over the past fifteen years, the spotted-wing drosophila (Drosophila suzukii) has become a major threat to soft-skinned fruit crops worldwide. Despite various control strategies, integrated pest management still relies heavily on insecticides, leading to significant economic and environmental concerns. As an alternative, biological control has been explored, with the introduction of Ganaspis kimorum (formerly G. brasiliensis strain G1), a parasitoid specific to D. suzukii (Stahl et al., 2024). Italy was the first country in Europe to adopt this approach, importing G. kimorum in 2020 for quarantine testing at the Edmund Mach Foundation (FEM) in Trentino. By 2021, the Italian Ministry of Ecological Transition authorized a national biological control plan, expanding its scope to multiple regions over the following years (Lisi et al., 2021). Despite significant challenges, the program represents a crucial step toward sustainable pest management. Key difficulties included genetic bottlenecks in G. kimorum populations, mass-rearing constraints, logistical hurdles in distribution and release, and regulatory delays. Genetic diversity loss due to inbreeding raised concerns about the parasitoid’s adaptability. Additionally, G. kimorum requires fresh D. suzukii-infested fruit for reproduction, making mass-rearing costly and complex. Mite infestations further complicated rearing efforts. Logistics also played a critical role, as transportation conditions affected parasitoid survival. Selection of release sites prioritized low-chemical environments to maximize establishment success. Extensive pre- and post-release monitoring assessed establishment rates and non-target impacts (Fellin et al., 2023). After four years of releases, G. kimorum has established itself in some northern regions, particularly in Trentino and Valle d'Aosta, though results vary by region. Southern areas faced challenges due to high temperatures and droughts, which reduced host availability. Despite limited immediate impacts on D. suzukii populations, parasitoid presence and spatial expansion have increased over time, suggesting long-term potential for biological control. The Italian biological control program has made notable progress in optimizing rearing techniques and refining release strategies. Continuous improvements in monitoring, technological advancements, and stronger collaboration between research institutions, regulatory bodies, and agricultural stakeholders will be essential to enhancing the program’s success. While challenges remain, the initiative represents a promising step toward reducing dependence on insecticides and promoting sustainable pest management.