Pollination of the Orchid Habenaria rhodocheila by the Swallowtail Butterfly Papilio helenus in Subtropical Evergreen Broad-Leaved Forests in Southern China

Habenaria rhodocheila is different from other species in the genus as it has bright yellow-orange, orange-red or red floral colors and grows in subtropical evergreen broad-leaved forests. It is listed as a level II protected plant in China. This study focused on details of the pollination mechanism, including floral structure, the pollinator and its behavior, the pollination process, and fruit set in its natural environment compared to controlled artificial pollination. Our results showed that the flowers of H. rhodocheila are self-compatible, but rely on a pollinating agent due to the lack of an automatic self-pollination mechanism. At three sites the flowers of H. rhodocheila were frequently pollinated by a species of the swallowtail butterfly Papilio helenus L. During pollination, the butterfly inserts its proboscis into the spur aperture. The base of the proboscis then contacts the viscidia and the pollinarium sticks to the insect, followed by contact between pollinia and stigmas. The length of the proboscis of P. helenus is comparable to, but slightly shorter than the length of the floral spur. The pollination activity generally occurs between 9:30 AM to 1:30 PM daily and is especially frequent between 10:30 AM and 11:30 AM. These results suggest that the similarity between the length of the butterfly's proboscis and the length of the orchid's spur is a major factor contributing to the efficient pollination of H. rhodocheila in its natural habitat. Most species in Habenaria are moth-pollinated, whereas our research has shown that H. rhodocheila in subtropical evergreen broad-leaved forests in China is specifically adapted to butterfly pollination by P. helenus.