Pollination biology of Sicyos angulatus: An invasive plant primarily pollinated by the native insects and introduced honeybee Apis mellifera

Burcucumber (Sicyos angulatus), first introduced in 1952 from North America to Japan, has recently become a seriously invasive alien species that has spread nationwide. The pollination mode is likely to play a crucial role in seed production and invasion. Burcucumbers have been characterized as self-compatible flowers with distinct anthers and stigmas, indicating pollen vector-mediated pollination. In this study, we aimed to describe the floral biology of burcucumbers and clarify their relationships with pollinators. We found that: (1) primarily native insects (at least 70 species) repeatedly visited burcucumbers, both during the day and night; (2) in terms of visitation frequency and pollen-carrying load, honeybees, vespid wasps, and hoverflies were the most important diurnal pollinators, followed by sphingid and noctuid moths as nocturnal ones; and (3) the production of highly concentrated nectar as floral reward coupled with floral scents, predominantly aliphatic compounds such as heptanal and hexanol, may mediate the visitation of floral visitors. Our observations confirmed that burcucumber visitation is dominated by native pollinators, indicating the integration of burcucumbers into native pollinator webs. Our findings highlight the significance of a generalized pollination system in alien plants to overcome reproductive failure within a new region.

Automated summary

Burcucumber (Sicyos angulatus), an invasive alien species introduced from North America to Japan in 1952, has spread nationwide. This study aimed to describe the floral biology of burcucumbers and their relationships with pollinators. Native insects, including honeybees, vespid wasps, hoverflies, sphingid moths, and noctuid moths, were identified as the main pollinators. The production of highly concentrated nectar and floral scents, particularly aliphatic compounds, may attract floral visitors. The integration of burcucumbers into native pollinator webs highlights the importance of a generalized pollination system in alien plants to ensure reproductive success in new regions.