Pollination studies in East Asia have been developing rapidly in recent decades. East Asia may provide important information on many aspects of plant-pollinator interactions because of the rich fauna and flora and highly heterogeneous environments that occur there. In this review, plant-pollinator interactions in East Asia were summarized. Bumblebees are important pollinators of many plant species in East Asia, as well as in Europe and North America. Native honeybees may also have important roles in pollination in East Asia. Bird pollination and hawkmoth pollination may be less common in East Asia than in North America. Geographic variation in pollination interactions is expected because several types of pollinators are rare or absent in some habitats or geographic regions. For example, specialized nectar-feeding vertebrates like sunbirds and pteropodid bats are absent from most of East Asia except for some areas in its southern part. Opportunistic nectar-feeding vertebrates may have important roles in pollination where specialized nectar-feeding vertebrates are absent. Human impacts on plant pollinator interactions are understudied in this region. However, climate change, habitat degradation, and invasive species may have negative impacts on plant-pollinator interactions and thus plant reproductive success there. The information available on the plant-pollinator interactions in East Asia is still limited because many plant and pollinator taxa and many types of habitats are understudied.

The discrepancy between observed flower visitors and those predicted based on floral phenotype has often cast doubt on the pollination syndrome concept. Here we show that this paradox may be alleviated by gaining better knowledge of the contributions of different flower visitors to pollination and the effects of floral traits that cannot be readily perceived by humans in Adenophora triphylla var. japonica. The blue, bell-shaped and pendant flowers of A. triphylla appear to fit a bee pollination syndrome. In contrast to this expectation, recent studies show that these flowers are frequented by nocturnal moths. We compared the flower visitor fauna, their visitation frequency and their relative contributions to seed set between day and night in two field populations of A. triphylla in Japan. We also determined the floral traits associated with temporal changes in the visitor assemblage, i.e. the timing of anthesis, the timing of changes in the sexual phase and the diel pattern of nectar production. While A. triphylla flowers were visited by both diurnal and nocturnal insects, the results from pollination experiments demonstrate that their primary pollinators are nocturnal settling-moths. Moreover, the flowers opened just after sunset, changed from staminate to pistillate phase in successive evenings and produced nectar only during the night, which all conform to the activity of nocturnal/crepuscular moths. Our study illustrates that the tradition of stereotyping the pollinators of a flower based on its appearance can be misleading and that it should be improved with empirical evidence of pollination performance and sufficient trait matching.

Generalized pollination systems may be favored in early spring flowering plants, as during this period pollinator activity is unpredictable. Many previous studies have concentrated on the importance of diurnal visitors in pollination, and consequently, information on the contribution of nocturnal visitors to pollination in early spring is limited. This study was conducted to evaluate the relative importance of diurnal and nocturnal pollinators in the early spring flowering dioecious shrub Stachyurus praecox (Stachyuraceae), in two temperate forests in central Japan. Visitors to the female and male flowers were observed during day and night, and their relative contributions to seed set were compared. The pollinator observations revealed that the diurnal and nocturnal insects visited both male and female flowers, and that the main flower visitors were diurnal small bees and flies as well as nocturnal settling moths. The diurnal and nocturnal flower visitors also acted as pollinators, as the pollen grains of S. praecox were attached to the insects collected from the female flowers. Pollination experiments demonstrated that the contributions of diurnal pollinators to the seed set were higher than those of the nocturnal pollinators. The results of this study indicate that S. praecox has a generalized pollination system, comprising both diurnal insects and nocturnal settling moths. Although the roles of diurnal insects are more important in the pollination of S. praecox, nocturnal settling moths may have a complementary role in early spring.

Abstract. Nocturnal pollinators such as moths have received less attention than diurnal insects. To elucidate whether nocturnal moths are important pollinators, we observed both the diurnal and nocturnal visitors to the fl owers of Uncaria rhynchophylla (Rubiaceae) in a warm-temperate forest in central Japan. The diurnal visitors included various taxonomic groups (e.g., bees, hoverfl ies and butterfl ies). The nocturnal visitors were exclusively moths (Geometridae, Erebidae, Noctuidae and Crambidae). Pollen grains of U. rhynchophylla were attached to both diurnal and nocturnal visitors. Although diurnal fl ower visitors carried pollen grains of other plant species, nocturnal moths did not carry heterospecifi c pollen grains. These results suggest that nocturnal moths, as well as diurnal insects, are important pollinators of U. rhynchophylla.