The screening mechanism is an important component of the screening game
between plants and pollinators, and also as a theoretical framework for
understanding the maintenance and drivers of co-evolution by animals and
plants. However, no previous studies have investigated the composite
screening mechanism in plants from biomechanical and morphological
perspectives. Thus, we observed and measured the insects and flower
traits in different populations of Delphinium caeruleum J., and compared
the operative strength of staminodes with the strength that insects were
capable of exerting, as well as the length of the nectar spur and
proboscis in insects. The flower traits, insect species, visitor
frequency, and efficiency differed among three experimental sites. The
strength and proboscis length of the insect visitors matched with the
operative strength of staminodes and the nectar spur length, whereas the
opposite was found for non-visitors. Our results demonstrate that
Delphinium caeruleum J. can screen for efficient pollinator insects
through a complex mechanism based on a combination of length screening
and biomechanical screening. Pollinators contribute significantly to
promoting both the convergence and divergence of flower characteristics,
which may be a consequence of plants adapting to local pollinators.