Abstract: The occurrence of nectarlessness flowers in nectar-producing plants is a common and stable phenomenon in many species, but their occurrence is still not well understood. The aim of this study is to examine a question from both the plant and pollinator perspectives: why do nectar-producing species produce some nectarless flowers within a plant? We investigate the distribution patterns of nectarless flowers in natural populations and their variation among the populations and years in a spring-flowering self-incompatible perennial herb plant, Corydalis ambigua Chem. & Schlecht (Fumariaceae), we observed the foraging behavior of bumblebees to nectariferous and nectarless inflorescences. We also examined the differences in reproductive success between inflorescence types and the effect of nectar production on flower production of the next flowering season. The results indicated that the frequencies of nectarless flowers varied among inflorescences, individuals, and populations and between years. Plants can revise or keep their inflorescence types or change nectar production status in the next growing season. Bumblebees visited both types with equal frequency but different foraging behavior, which resulted in lower seed production in nectarless inflorescences. However, nectarless inflorescences may save more energy and result in larger bulbs, which produce more flowers in the next flowering season. We found that although nectarless flowers resulted in lower seed set in nectarless inflorescence or individuals, they could affect bumblebees’ foraging behavior and further promote the effective output of pollen. In addition, the resource savings could enhance plant reproductive success in the next flowering season.

Key words: Bombus, bumblebee, Corydalis ambigua, cost of reproduction, foraging behavior, nectarless flower, reproductive strategy