The diversity of flower-visiting insects in the gardens of English country houses

Flower-visiting insects provide essential pollination services, ensuring both global food security and the continuity of wild plants. Recently documented declines in pollinators give cause for concern. Identifying previously unappreciated habitats that support diverse assemblages of these insects is an essential first step in mitigating further losses. This study evaluates, for the first time, the role that large English country-house gardens play in supporting flower visitors within expanses of intensively farmed agricultural land. Focussing on 17 properties in lowland Central England, the results show that these novel ecosystems are important sites for hoverflies, bees and butterflies. In 2010 almost 10,000 flower-visitors from 174 species were recorded Hoverflies were the only group to show a significant difference in species richness across the sites. An important characteristic of these rural gardens is the high diversity of flowering plants available. More than a fifth of the world's plant families were represented, of which approximately 68% were non-native. The results showed that flower visitors did not prefer native plants over aliens, and that the dominance by aliens was no barrier for extensive use by the insects present. Both the species richness and abundance of flower visitors increased as plant richness increased. The study revealed that half of all insect-plant interaction networks examined exhibited a nested structure, a common feature of natural environments that has not previously been assessed in rural gardens. In addition to flower resources influencing insect species richness, landscape-scale effects were also significant. Insect groups responded differently to components in the landscape according to the time of year and the spatial scale considered. Bumblebees exhibited the greatest response to landscape factors and did so at larger scales than other groups. The deployment of commercial trap-nests for solitary cavity-nesting red mason bees in walled gardens revealed new insights into the differential mortality suffered by male and female progeny. Female offspring were found to be disproportionately affected by a combination of development and parasitism losses. This finding suggests that effective mitigation strategies are needed before this species can be considered for use as a managed-pollinator. Further research assessing the benefits crops such as oilseed rape derive from the presence of insects in nearby rural gardens would be a useful addition to this work. Overall, the gardens of English country-houses emerge as sites of important natural as well as cultural heritage.