Set-aside of grassland field margins enhances buckwheat pollination services in small-holder agricultural landscapes

Smallholder agricultural landscapes, which are commonly found in Asian countries, harbor large areas of semi-natural grasslands because of the high density of field margins, which could potentially function as habitats for diverse pollinators. However, its function has not been fully realized owing to intense mowing management in recent years. This study clarified the ecological process by which the set-aside practice in field-margin grasslands enhances buckwheat pollination services. We conducted a field experiment over three years in Japan and investigated insect visitation and seed sets of buckwheat in fields with conventionally mowed and set-aside margins. Insects visiting buckwheat fields were more abundant in fields with set-aside field margins, and seed sets also increased in fields with set-aside margins because of increased insects. This tendency was consistently observed across all years and seasons. Moreover, insects with a broader utilization of wildflowers contributed more to the seed sets. The abundance responses to set-aside practices differed among insect groups. Non-bee insects increased with the set-aside practice, whereas bees did not. Seed sets increased with an increasing abundance of wild bees, hoverflies, and flower chafers, but not with honeybees. Our results indicate a causal link between set-aside grassland field margins and an increase in buckwheat pollination services. In particular, non-bee insects primarily drive the positive effects of set-aside practices on buckwheat pollination. We propose that exploring appropriate management of existing field margins, rather than setting grasslands inside the fields, which can boost pollinators and crop pollination services, is promising in smallholder agricultural landscapes.