Identifying insects pollinating crops is a fundamental step for sustaining crop production, as most crop species rely on animal-mediated pollination. Crop pollination studies have primarily focused on the diurnal insects as pollinators. On the other hand, the role of nocturnal pollinators has been largely overlooked, despite its prevalence in wild plant species. Buckwheat (Fagopyrum esculentum) depends on insect-mediated pollination because of its self-incompatibility with distylous flowers. Since buckwheat flowers are believed to open in the morning and close in the evening, all studies so far examined the role of diurnal pollinators (e.g., Hymenoptera, Diptera, Coleoptera, and Lepidoptera). However, we observed that some flowers were still opening at night and seemed to provide nectar. Accordingly, we expected that nocturnal insects, particularly moths, visit buckwheat flowers and contribute to buckwheat pollination services.
Field surveys were conducted in Iijima town, Nagano prefecture, central Japan, in 2022. Moths visiting buckwheat flowers were collected using an insect net from 19:00 to 21:00. Then, the number of pollen grains on the collected moths' bodies was counted. To compare the pollination contribution between diurnal and nocturnal pollinators, we conducted an insect exclusion experiment with four bagging treatments; no pollinators (bagged inflorescences for 24h), only diurnal pollinators (bagged from 18:00 to 06:00), only nocturnal pollinators (bagged from 06:00 to 18:00), and control (not bagged). After the buckwheat blooming period, we collected all inflorescences and calculated seed sets.
In total, 27 moths belonging to Crambidae, Geometridae, and Noctuidae were collected in buckwheat fields. Noctuidae was the most common family (65%). These moths were attached 471.0 ± 500.4 pollens on their bodies (mean ± SD, min = 0, max = 2453). Pollen count was higher in the following order: Noctuidae, Geometridae, and Crambidae. The insect exclusion experiment showed that the seed sets were significantly higher in the following order: control (0.37 ± 0.10, mean ± SD), only diurnal pollinators (0.28 ± 0.12), only nocturnal pollinators (0.10 ± 0.06), and no pollinators (0.01 ± 0.02). Remarkably, nocturnal moths contributed to one-fourth of buckwheat pollination on average.
These results indicate that nocturnal moths are effective pollinators of buckwheat, representing the first report of nocturnal pollination by moths on globally cultivated crops. The present study emphasizes the need to investigate overlooked nocturnal pollinators in the study of crop pollination services.