Contrasting the farm-scale spatio-temporal dynamics of boundary and field overwintering predatory beetles in arable crops

In many European countries agri-environment funding can improve ecosystem services, including the adoption of conservation biocontrol, through the creation of habitats that encourage beneficial arthropods. Predatory beetles are amongst the most numerous and diverse arthropods present in arable fields. The primary ecosystem services provided by predatory beetles are in biological control and food chain maintenance as they are a key resource for many higher organisms. However, to be effective biological control agents, able to respond quickly to wherever a pest infestation occurs, then they must be sufficiently abundant and widely distributed. Conservation biocontrol utilising predatory beetles has focussed on the impact of species that overwinter in adjacent field boundaries, although those overwintering within fields are often more abundant. If the abundance and distribution of predatory beetles is to be maximised then further knowledge of their spatial dynamics is required to ensure habitats are arranged appropriately. The spatio-temporal dynamics of boundary and field overwintering species was measured across 64 ha encompassing six fields and for three consecutive years using a grid of 973 pitfall traps. Boundary species were more numerous in spring (May and June) whereas more field species were captured in July. The species composition was comprised of relatively few taxa. Boundary species occurred in small patches that were distributed across the fields in spring, but were only found close to the margins in July. Patches persisted in some locations over two years. Field species occurred in larger patches, spread across particular fields and these were stable within years and to some extent between years. Game-cover strips were attractive to boundary species in the spring and summer and did not effect predator distribution in the adjacent crop.