Many invasive plant species have generalized pollinators and/or have the capacity for self-fertilization, thus avoiding disruptions in seed production when interacting with novel pollinator assemblages in introduced ranges. However, the common invasive vine, Lonicera japonica, is specialized for pollination by nocturnal hawkmoths and seed production is dependent on receiving biotically transferred pollen from a genetically distinct individual. Lonicera japonica is morphologically plastic, and under favorable conditions continues to produce new flushes of lateral shoots throughout its growing season. Because the flowers of L. japonica are produced in paired axillary inflorescences, flowers are produced throughout the growing season on each new flush of shoots. We observed that flowers borne on the first shoots to elongate produced few fruit compared to flowers produced on lateral shoots formed later in the year. We asked how the flower visitors to L. japonica changed over time as first primary shoots flowered, and then later as secondary shoots flowered. We recorded all visitors to flowers borne throughout the season and quantified their fruit set. We specifically asked it hawkmoths provided more effective pollination than small bodied bees and flies by enclosed flowers within large mesh exclusion bags that limited flower visitation to small-bodied insects.
Results/Conclusions
The extended flowering period of Lonicera japonica exposed flowers to different pollinators throughout the growing season. Flowers open early on primary shoots received less than one pollinator visit per day and produced fruit from 12% of flowers. No hawkmoths visited these early opening flowers. In contrast, flowers opening later on secondary flushes of shoots were visited by 3 pollinators per day and increased fruit to 60%. These later opening flowers were visited by hawkmoths and small bees reported as pollinators in the native range. The highest rate of flower visitation we documented was by the diurnal hawkmoth, Hemaris diffinis. When flowers were not visited by hawkmoths, either because they opened before hawkmoths were active or were enclosed within large-body pollinator exclusion bags, their fruit and seed production was limited. We conclude that hawkmoths are critical to successful fruit set in L. japonica and that L. japonica could be an important nectar source for local hawkmoths. Further, we conclude that the capacity to flower multiple times allows L. japonica to overcome a mismatch between its primary flowering event and hawkmoth flight times in Arkansas.