Forest habitats improve biological control of Drosophila suzukii

To date, significant efforts have been made to promote the biological control of Drosophila suzukii outside its native range. Recently, classical biological control using exotic parasitoids, both intentionally and accidentally introduced, has attracted considerable interest. In particular, adventive populations of Leptopilina japonica have been rapidly expanding in Europe and North America. In this study, we assessed how D. suzukii density, host plant species, season, and landscape composition and configuration influence this exotic parasitoid. We sampled elderberry, wild blackberry, and pokeweed fruits over two years from 27 sites in northeastern Italy selected to represent statistically independent gradients of forest cover and forest patch density. L. japonica exhibited a strong host-density response at the local scale, enabling it to track the temporal and spatial distribution of D. suzukii. This led to higher parasitism rates in late summer and in landscapes with greater forest habitat cover. Parasitism rates observed in plant species associated with forest habitats were positively correlated with forest cover and high patch density, highlighting the pivotal role of these habitats in supporting the biological control of D. suzukii. Thus, preserving complex agricultural landscapes is crucial for promoting biological control of D. suzukii and for facilitating the establishment of viable populations of natural enemies in pesticide-free areas where natural pest-regulation processes can operate.