Identifying crop pollinators and the environments that support their diversity is crucial for sustaining crop pollination services. Most crop pollination studies focused on diurnal pollinators, while nocturnal pollinators have been largely overlooked. Buckwheat, which is self-incompatible with distylous flowers, depends on insect-mediated pollination. Generally, buckwheat flowers are believed to open from early morning to evening, while we recently found that 80% of flowers remain open at night and, nocturnal moths contribute to buckwheat pollination based on a pollinator exclusion treatment. However, how nocturnal moths play a role in natural conditions, when diurnal pollinators are also present, remains unclear. In this study, we aimed to reveal (1) the role of nocturnal moths in buckwheat pollination in the presence of diurnal pollinators, and (2) how environments surrounding farmlands (field margin vegetation and broadleaf forest) influence the abundance of nocturnal moths visiting buckwheat. Field surveys were conducted in June and September 2024 in Iijima, Nagano Prefecture. Diurnal (09:00 – 12:00) and nocturnal (19:00 – 22:00) insects visiting buckwheat flowers were collected, and seed set was measured using collected inflorescences. A hierarchical model was used to analyze the causal chain between the surrounding environments, insect abundance (both diurnal and nocturnal), and seed set. We collected 1,439 diurnal insects from four orders (Hymenoptera, Diptera, Lepidoptera, Coleoptera) and 541 nocturnal moths from five families (Noctuidae, Crambidae, Pyralidae, Geometridae, and Sphingidae). The estimated abundance of both diurnal and nocturnal insects was positively correlated with vegetation height at field margins and broadleaf forest areas. Small moths increased with vegetation height, while large moths with broadleaf forest. Seed set was positively correlated with the estimated abundance of both diurnal and nocturnal insects. Moreover, their interaction played a role, with nocturnal moths making a notable contribution to buckwheat seed set when diurnal insects were less abundant. These results suggest that nocturnal moths compensate for a shortage of diurnal pollination and that surrounding semi-natural habitats are essential for sustaining complementary roles among diurnal and nocturnal pollinators. This study highlights the need to reveal not only the overlooked roles of nocturnal pollinators but also the environments that support them in the studies of crop pollination services.