182 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



Moapa Valley, Nevada, are most likely i. discoloratum. No tents of any 

 kind were located on cottonwoods along the Colorado River and the 

 reservoirs from Boulder City to Yuma, Arizona, despite several days 

 spent searching the area around Davis Dam, Needles, Topock, Parker 

 Dam, Parker, Blythe, Yuma, and San Luis. Some form of M. incurvum 

 should be found on cottonwoods along the river in these areas since 

 adults have been seen from Yuma. Also some form of M. californicum 

 probably occurs in the hills along the river, but none has been seen to 

 date, except for a single male from Cibola, Yuma County, Arizona. 



COMMENTS. — This subspecies is recognized because it seems to be 

 quite well separated geographically from M. incurvum incurvum, and 

 because most of the larvae are easily separated from i. incurvum (figs. 

 390-394) by the presence of a dorsal stripe on most of them, and by the 

 lack of conspicuous tufting of the lateral setae. Larvae of i. incurvum 

 almost never have a dorsal stripe, and the lateral setae are usually 

 conspicuously tufted. There are less consistent differences in the color 

 of the adults and larvae, too, but in other respects such as hosts, egg 

 masses, color of spumaline, tents, etc., they are virtually identical. 



M. incurvum discoloratum may be related to the aspen populations of 

 M. californicum in a way similar to that suggested in the section on 

 "The Western Tentbuilders" (page 118), An example of a population 

 that may be a connecting link is Collection No. 305 which was similar 

 to the aspen populations of M. californicum in most respects, the greatest 

 differences being the fact that it was on Popidus angustijolia which is 

 sometimes a host of i. discoloratum, and that it occurred at an elevation 

 of 6100 feet (below the aspen zone, but lower than the highest elevation 

 where i. discoloratum has been found — 6700 feet, Coll. No. 313). 



Some connecting populations between i. discoloratum and other 

 populations of M. californicum which do not have specks in their spum- 

 aline may also exist, but none were found during this study, although 

 some adult males of Collection Nos. 313 and 284 (fig. 303) had a 

 browner median area on the forewing than "normal" i. discoloratum 

 males. This could be due to some introgression of genes from M. 

 californicum populations which normally have a dark median area. 



Specimens Examined. — 624 (Museum specimens — 51 males, 13 females, 49 

 larvae; reared specimens — 265 males, 246 females, plus numerous larvae and 

 egg masses). See Appendix I for collections made during this study (page 290). 



United States, — Arizona: Mohave Co. Nevada: Clark Co.; Mesquite; 

 "S. Nevada." Utah: Bellevue (Washington Co.); Bluff; Capitol Reef Nat. 

 Men.; Moab; Santa Clara; St. George; Entrance, Zion National Park; Zion 

 National Park; Zion Canyon; "Utah." 



