REVISION OF MOTHS OF PRODOXINAE 35 



extranea to be diurnal in their movements. Pollen collecting, ovi- 

 position, pollination, copulation, and flight were all noted during the 

 daylight hours. Mention was not made as to when these activities 

 ceased, or if they were continued into the night at a greater or lesser 

 frequency. The behavior of T. synthetica is similar to that of T. 

 yuccasella in that the moths rest during the days in the flowers and 

 become active toward evening. 



As noted by Riley, Trelease, and others, a tendency seems to exist 

 for the females to frequent only the newly opened blossoms of the 

 Yucca. This, of course, has a practical advantage in that the females 

 are directed away from flowers which most likely have already been 

 pollinated and supplied with eggs; thus, this may be a means of in- 

 suring a more uniform distribution of the larvae. It is not fully 

 understood how the females are directed to fresh blossoms, but in 

 some instances (as observed for T. synthetica) the partially unopened 

 condition of the young flower may aid in selection. The relative age 

 difference and degree of flower odor between old and new blossoms 

 may provide the deciding factor for most yucca moths. A desire to 

 imbibe nectar or any comparable plant substance can have no attrac- 

 tion for the moths due to the vestigial condition of their mouthparts. 

 Furthermore, the nectar glands of the yucca flower are reduced in size 

 and open near the base of the pistil. Secretions from these glands do 

 attract some insects but seldom in large numbers. It may be of 

 interest to note here that these insects are not likely to be in any way 

 involved mth pollination due to the relative remoteness of the 

 glands from the stigma. 



It is interesting to speculate upon the mutual dependency the genus 

 Yucca and its pollinators exhibit in their unusual association. Super- 

 ficially, one appears equally dependent upon the other for siuvival, 

 and thus display a true symbiotic relationship. In actuahty it may 

 be that the yucca moth profits most from this association (at least 

 for the present) and, therefore, demonstrates a greater dependency 

 upon its host. 



It seems certain that the great majority of yuccas would never bear 

 fruit if it were not for the dehberate act of pollination performed by 

 the moths. Other insects have been reported visiting the flowers, 

 but none have been observed to act as pollinators. The writer has 

 frequently noted cultivated yuccas in Washington, D.C. Nvhich have 

 flowered durmg the autumn months without ever producing fruits. 

 Similar observations have been reported by numerous authors; 

 whenever the adult moth is not present, then fruiting of yucca usuaUy 

 does not occur. Since the first publication of this association in 1872, 

 however, the fruiting of certain yuccas has been noted in areas 

 where Tegeticula was known to be absent. Riley (1891b) refers to 



