22 U.S. NATIONAL MUSEUM BULLETIN 255 



the flowers. Flower captures often do indicate the larval food plant 

 for this group of insects, but errors can occur; for this reason, I have 

 noted with a question mark in table 1 any record which I considered 

 dubious. 



The systematics of the genus Agave is even more complicated than 

 that of Yucca. A tremendous variety of morphological types exists 

 which has fostered a great amount of superficial taxonomic activity, 

 resulting in a copious supply of specific names. In his monograph 

 of the genus, Berger (1915) recognized 274 species of Agave; approxi- 

 mately 185 species have been described from Mexico alone (Trelease, 

 1920). 



One of the principal factors for the apparent success of Agave has 

 been the high development of polyploidy throughout the group. 

 Whereas all species of Yiicca, as far as known, are diploid (n=30), 

 a euploid series of 2n, 3n, 4n, 5n, and 6n, with a basic number of 30, 

 has been discovered in Agave (Granick, 1944). Both autopolyploidy 

 and allopolyploidy probably occur, although more evidence is availa- 

 ble to support the latter. A definite correlation exists in Agave 

 between polyploidy and vegetative growth, similar to that observed 

 in other plant groups; namely, that the polyploids tend to be more 

 robust and are characterized by leaves which are larger and more 

 succulent than those of the diploids. It seems very likely that 

 polyploidy, in connection with hybridization, has been largely re- 

 sponsible for many of the taxonomic problems encountered in this 

 group of plants. 



The center of distribution for Agave, in contrast to that of Yucca, 

 is situated further south, in Mexico, as indicated by the number of 

 species indigenous to that country. Granick (1944) reached a similar 

 conclusion on the basis of chromosome data. Because diploid forms 

 usually represent the ancestral types in such a group of plants, their 

 heaviest concentration should be near the distributional center for 

 the group. Consequently, one finds several diploid species in Central 

 America but only two such forms as far north as Arizona. Toward 

 the northern limit of its range. Agave is represented principally by 

 tetraploids and some hexaploids. 



Although Agave possesses a many seeded, capsular fruit similar to 

 that of Yucca, it is very doubtful that any member of the Prodoxinae 

 has evolved as a seed borer in this plant. It is noteworthy in this 

 regard to mention that the nectaries of the flowers are weU developed 

 and quite odoriferous. Consequently, numerous hummingbirds are 

 attracted as well as a great variety of insects (primarily bees and 

 flies), which result in the pollination of the flowers. 



The relationships between Yucca and Agave, which appear relatively 

 close as indicated by the biology of the Prodoxinae, have not been 



