Hawkmoth Pollination of Aquilegia chrysantha (Ranunculaceae) in Southern Arizona

Abstract

A. chrysantha occupies mesic habitats in moutainous regions of the southwestern USA and northern Mexico. The faintly scented, yellow flowers are protandrous and the spurs secrete large quantities of nectar (29% total sugars). Seed set for plants under cages was 31% compared with 55% for open-pollinated flower. The most common pollinator of the species in the Chiricahua Mountains was the crepuscular hawkmoths Eumorpha achemon (Sphingidae), although 2 Sphinx species [S. asella and S. chersis] also foraged effectively for nectar. The mean tongue length (4.4 cm) of Eumorpha is relatively short compared with the length (6.7 cm) of the floral spurs of A. chrysantha. This suggests that longer-tongued hawkmoths such as the Sphinx (5.4 cm) may be more important pollen vectors for A. chrysantha than is indicated by their low frequency of visitation in this study. Diurnal visitation to A. chrysantha flowers at a very low rate by large bees and hummingbirds, or recent evolution as a moth-visited taxon, may account for the failure of this hawkmoth-pollinated species to have developed a strictly crepuscular or nocturnal anthesis.