Managing habitats on English farmland for insect pollinator conservation

Abstract

Agri-environment scheme habitats can support declining pollinators, but optimum approaches for deployment remain uncertain. The impact of three management treatments (project-, farm-managed and organic farming) alongside habitat type, quantity of uncropped land removed from production and spatial configuration (strips or blocks) on wild bees, butterflies and hoverflies were investigated. Pollinators were assessed on 28 sites over three years, along boundaries representing site scale (ca. 100-ha) and within project-managed (floristically enhanced grass, wild bird seed mix, insect rich cover and natural regeneration) or farm-managed wildlife habitats (typically grass margins or game cover). Project-management resulted in the creation of the most widely utilised habitats (floristically enhanced grass and wild bird seed mixtures), but these may attract wild bees away from boundaries whereas butterfly abundance (Lycaenidae and Pieridae) was enhanced along field boundaries. Organic management and spatial configuration of habitats had little impact. Proportion of uncropped land per site was positively related to Cuckoo bee, Lycaenidae and Satyridae density and butterfly species richness at site scale and on the density of several bee species, total wild bees, Pieridae and total butterflies in wildlife habitats. The mean abundance of uncropped land was 3.6% and at least double this was required to double the abundance of wild bees and butterflies. Wild bee densities were highest in field boundaries and floristically enhanced grass and positively correlated with flower cover. Butterflies sought habitats containing their larval food plants and high flower cover. Hoverflies were most abundant in the insect rich cover. Wildlife habitat in agricultural landscapes may be insufficient and additional, diverse habitats are needed to encourage pollinators.