In temperate regions, generalist insect pests are expected to use multiple habitats and host plant species over the different seasons. Landscape composition and configuration can also provide a diversity of thermal resources and host plants that can modify insect activity and movement. Here, we described the seasonal spatial distribution of a destructive invasive pest, spotted wing drosophila (SWD), along a gradient of landscape composition (i.e. proportion of forest habitat) and configuration (i.e. length of forest edge). We selected a triplet of habitat patches (forest, vineyard and grassland) in 17 landscapes in North-eastern Italy characterised by different proportions of forest and forest edge length and monitored pest activity density for 1year. We found that during the cold season, SWD mostly occupied forest habitats, which were suitable overwintering sites due to ideal microclimatic conditions. During plant-growing season, SWD occurred equally in the three habitats, probably due to warmer temperatures in open areas as well as high food and host availability. In summer, when high temperatures can be limiting, landscapes with large forest edge length presented an increase in activity density compared to landscapes with less amount of edges, irrespective of the total cover of forest. Large edge length indicated landscapes with high contact zones between forest and open habitats, probably favouring spillover of individuals in SWD. In the light of these results, pest control in crop fields located in landscapes with complex configurations can be particularly challenging. The high density in non-crop habitats suggests that this invasive species can have pervasive impact also on wild plant species occurring in semi-natural and natural habitats.
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