Studies on ecology and behavior of Japanese black swallowtail butterflies. 6. Nectar feeding of Papilio helenus nicconicolens Butler and P. protenor demetrius Cramer as main pollinators of glory bower, Clerodendron trichotomum , Thunb

The butterflies Papilio helenus and P. protenor were shown to feed mainly on the nectar of the glory bower, Clerodendron trichotomum , which was the most abundant nectar plant in summer in the study area. Both the species were found to have a proboscis longer than 24 mm corresponding to the length of the corolla tube of C. trichotomum . Visits to the flowers by these butterflies were observed more frequently than visits by sphingid moths which had previously been believed to be the major pollinators of C. trichotomum . The male butterflies visited trees of C. trichotomum frequently, while visits by the females were less frequent. However, once females had visited the tree of C. trichotomum , they remained there longer than the males. Since the flower of C. trichotomum has long protruding sexual organs, its pollen grains were found to adhere efficiently to the bodies of butterflies, mainly the thorax, during nectar feeding. Most of the butterflies became loaded with C. trichotomum pollen, and the mean number of pollen grains per butterfly was 1,776 for P. helenus and 2,817 for P. protenor . The flowers opened at any time of day but more frequently in the morning. The nectar was secreted throughout the day. In the maturation of the protandrous flower of C. trichotomum , the duration of the pistillate phase was about twice as long as the staminate phase. The long flowering period and the short duration of the staminate phase resulted in asynchrony of the flowering stages even within a single cyme on a tree. Such asynchrony and the abundance of attractive flowers on a tree facilitates efficient pollination by the butterflies.