Trumpet creeper is self-incompatible and bears long, tubular orange flowers from June-Sept. Flowering peaks rapidly, then declines and continues at low levels for several weeks. The initial burst of flowering may attract pollinators that return even during subsequent reduced flowering. Most flowers open before noon and nectar production totals 110 .mu.l of 26% sucrose equivalents per flower, an exceptionally high production for a temperature zone plant. Production ceases within 20-30 h of flower opening, but corollas persist for several days and may attract pollinators. Effective pollination reduces the period of stigma receptivity and speeds closing of stigma lobes. Only 1-9% of flowers produced mature fruits at 4 sites in Illinois and Missouri [USA]. About 400 pollen grains had to be deposited on a receptive stigma to cause fruit development beyond an initial period of high abortion. At 2 sites, 17% and 89% of stigmas received > 400 pollen grains. Assuming 50% of deposited grains were from the same plant, fruit production at 1 site was pollinator limited, that at the 2nd site may have been. Ruby-throated hummingbirds (Archilochus colubris) deposited 10 times as much pollen per stigma per visit as honeybees (Apis mellifera) and bumblebees (Bombus spp.). Fruit set was highest where rubythroat visitation was most frequent. Trumpet creeper appears primarily adapted for hummingbird pollination, but can be adequately pollinated by honeybees and bumblebees. This is one of the 1st attempts to relate pollen-depositing capabilities of pollinators of any plant to pollen requirements for fruit production. Apparently, trumpet creeper may be adapted to pollination at low densities (often called trap-lining) in its presumed original, woodland, habitat.
