Yuccas and Yucca Moths-A Historical Commentary

Abstract

The famous yucca-yucca moth pollination mutualism is presented in simplified, idealized form in most biology text books and some books on pollination biology itself. In fact, the interaction is probably more complicated than any single account has implied. It was first noticed in 1872 by George Engelmann but worked on much more by entomologist C. V. Riley and botanist W. Trelease. A conventional statement of the sequence of events is given and the complications are considered. References to seed setting in the absence of Tegeticula are reported that may be due to self-pollination or to the activities of other flower visitors. A nectar reward is provided by septal nectaries at the base of the ovary in many species of Yucca. There is disagreement among authors as to whether plants of some species are self-compatible and as to the extent of geitonogamy in various species. Tegeticula yuccasella appears to be the pollinator of all yucca species east of the Rockies and all the western species except Yucca whipplei (sensu lato) and Y. brevifoha. Yucca whipplei is served by Tegeticula maculata, which is diurnal in operation and has to contend with a capitate stigma. Yucca brevifolia also has its own species of yucca moth (T. synthetica). Natural hybridization appears to be rampant in the species pollinated by T. yuccasella but not for the two western species that have separate Tegeticula pollinators. There is some evidence, however, that T. yuccasella is a complex of taxa separately adapted to individual species of Yucca. Another genus is concerned with the pollination in Arizona and southeastern Mexico: Parategeticula, which has very different oviposition and larval behavior. Tentacleless Tegeticula occur in significant proportions in some populations and, like the bogus yucca moths, they are purely parasitic, not displaying any pollinatory activities. An attempt at placing these organisms