Lure of the locks: Showiest Ladies-tresses Orchids, Spiranthes romanzoffiana, affect bumblebee, Bombus spp., foraging behavior

Abstract

Unmarked bumblebees (Bombus bifarius workers) visited a 5 X 12 m patch of 12 Spiranthes romanzoffiana plants about every four minutes. The bees moved nonrandomly with respect to direction, zigzagging along a westerly-southeasterly path by foraging from the most "conspicuous" plants which were those with the tallest spikes and longest inflorescences. Spike height and inflorescence length were highly correlated both with the number of bee visits to individual plants and to each other. Bee visits were less influenced by the number of open flowers and the distances between neighboring plants. The bees performed nonrepeated foraging sequences 80% of the time, yet intensely revisited four of the most "conspicuous" plants. Repeated foraging sequences (20%) similarly involved many revisits to the most "conspicuous" plants. Thus, plant conspicuousness was the overriding factor that "lured" the bees to forage directionally in a patch of sparsely situated plants where revisits to the same plants occurred at higher rates than might have been optimal.