Semi-natural habitats boost Drosophila suzukii populations and crop damage in sweet cherry

Although increasing landscape complexity is often advocated as a key intervention to sustain pest biocontrol, little is known on how increasing semi-natural habitats surrounding the crop can directly affect the density and damage of generalist pests. Our aim was to test how semi-natural habitats in the landscape influences the density and the impact of spotted wing drosophila (SWD) on sweet cherry. SWD is invasive pest native of South-East Asia that causes severe yield losses in several crops worldwide. We selected 32 conventional cherry orchards in NE Italy surrounded by landscapes with different proportions of forest and we quantified both pest density and crop damage using sentinel fruits. We observed a larger attack density in orchards surrounded by higher forest cover. The same trend was observed for female adult density. Forest habitats may provide ideal microclimatic conditions and alternative host plants that can promote population growth. The effect size of forest cover on both adult density and crop damage, despite the very large tested forest gradient (0-60%), suggests that a reduction of forest cover does not seem to be a viable option for controlling SWD. Indeed, semi-natural habitats can deliver multiple fundamental ecosystem services to the crops (e.g. biocontrol). However, current integrated pest management should take into account landscape composition and interventions should be particularly timely in forested landscapes where SWD can quickly attack the crop at higher density.