56 U.S. NATIONAL MUSEUM BULLETIN 2 55 



C.V. value greater than 10 usually indicates, for linear, anatomical 

 dimensions of most animals, that the sample was not pure (Simpson 

 et al., 1960). Consequently, the above value of 18.577 strongly 

 suggests, at least on the basis of the male genitalia, that an additional 

 sibling species (or race) may be present within the moths currently 

 recognized as T. yuccasella. 



A second feature to be noted from table 2 is that the differences 

 observed in the genitalia do not seem to fall into a general or easily 

 defined pattern of distribution. In contrast, another character 

 studied, that of relative wing width, demonstrated a somewhat 

 simpler distribution in that the eastern forms tended to be broader 

 winged than the western. Specimens from several western localities 

 and Mexico exhibited genitalia within a general size range of 1.6 

 to 2.1 mm, as did all eastern males examined. Interspersed through 

 the southwest, however, are found populations whose males possess 

 more elongate genitalia. For example, the measurements of speci- 

 mens from four localities in New Mexico are listed in table 2; the 

 males from three of these areas display genitalia of a decidedly shorter 

 length than did those from Torrance County, which, in turn, were 

 comparable in size to certain males from Arizona and Utah. In 

 other words, if two sibling species (or races) are present among our 

 common yucca moth, as suggested by the samples studied in regard to 

 genitalia length, then the two entities probably are closely interwoven 

 in some areas, but not necessarily sympatric in the strict sense. 



In close connection with the preceding observation, it wUl also 

 be noted that there appears to be a correlation between host plant and 

 genitalia length. From the measurements in table 2, two size groups 

 can be recognized arbitrarily; one in which the length ranges from 1.6 

 to 2. 1 mm, and a second ranging in size from 2.2 to 3.0 mm. Specimens 

 reared or collected from Yucca baccata consistently exhibited maximum 

 lengths which feU within the latter group. These males also possessed 

 the most slender and elongate aedeagus, a character which is closely 

 correlated with genitalia size. 



Other yuccas also have served as hosts for moths tentatively listed 

 in the second group ; these species are : Yucca faxoniana (Trelease) 

 Sargent and Yucca "macrocarpa" (probably equivalent to Y. torreyi 

 Shafer of current literature). These three plant species, along with 

 others (see table 1), are included in the section Sarcocarpa, which is 

 characterized principally by fleshy, indehiscent fruit. The other 

 three sections of southwestern yuccas possess fruits which ripen as 

 dry capsides. The section Clistocarpa is monotypic (F. orevifolia), 

 possesses indehiscent fruit, and apparently never serves as a host for 

 Tegeticula yuccasella. The species of the sections Hesperoyucca and 

 Chenocarpa develop dehiscent fruit and the great majority, if not all. 



