20 U.S. NATIONAL MUSEUM BULLETIN 2 55 



and (3) major genetical. Variations produced by factors which 

 Webber considered as major genetical have caused some of the most 

 serious difficulties in understanding the genus, as this type of variation 

 is expressed frequently in hybrid combinations. 



Approximately 41 species of Yucca are recognized currently, al- 

 though, for reasons just stated, the application of several names is 

 questionable. The center of concentration for the genus is the south- 

 western United States, as evidenced by the presence of 21 species 

 (Webber, 1953) native to this area; previous authors listed as many as 

 28 to 32 species for the same region. Because no recent, comprehen- 

 sive reference on Yucca is available, several authors were consulted in 

 compiling the list of the species presented in table 1; some of the 

 principal works referred to were those of Trelease (1902, 1920), Small 

 (1933), McKelvey (1938, 1947), Feruald (1950), and Webber (1953). 



Webber's study of the southwestern yuccas superficially may appear 

 less thorough than the comparable work by McKelvey; however, I 

 have foUowed many of the decisions of the former author because his 

 concept of species and techniques employed seem more modern. 

 Several species proposed by McKelvey (e.g., Y. intermedia, utahensis, 

 verdiensis, campestris, kanabensis) were considered by Webber to 

 represent certain hybrid complexes and, consequently, were syn- 

 onymized. In the fists of host plants included in the foUowing 

 taxonomic treatments for each moth, I have retained McKelvey's 

 names, as given in her 1947 paper, in the event that a few may be 

 revived at some futm'e date. Those names which were synonymized 

 by Webber, however, have not been fisted in table 1. 



I have found it desirable to include a complete fisting of all species 

 of Yucca, even though several names have not been reported as food 

 plants for yucca moths. This was done primarily because it seems 

 almost a certainty that every plant eventuaUy wiU be found to harbor 

 at least one, and more probably two, species of moths. Also, because 

 no recent fist of yuccas was available, the presence of such a fist may 

 prove of some value, especiaUy in reference to certain problems dis- 

 cussed in connection with Tegeticula yuccasella (pp. 53-60). Several 

 subspecies of Yucca have been proposed, but since the status of these 

 names is even more uncertain than many of the presently accepted 

 species, and because the moths probably are not host specific at this 

 level, subspecific names have been excluded from table 1 . 



Much of the host information was summarized from the reports of 

 McKelvey (1947). It is possible that aU or most of her records were 

 based upon flower captures of the adults rather than upon actual 

 rearings. This is suggested by a lack of any definite statement that 

 rearings were performed, and more significantly by her remark 

 (1947, p. 184) that certain "other" Lepidoptera were collected from 



