168 UNITED STATES NATIONAL MUSEUM BULLETIN 276 



DISTRIBUTION (figs. 2, 3) —It is not possible to set exact dis- 

 tributional boundaries to the north, northeast, and east because of the 

 lack of specimens from some areas, but mainly because of the very 

 gradual and complete intergradation of c. fragile with the adjoining 

 central populations of M. californicum over a very large area. In the 

 northwest it intergrades with M. californicum recenseo near Lake Tahoe. 

 Its westward distribution seems to be limited by the Sierra Nevada, 

 although its relationship to M. californicum recenseo along the ridgeline 

 and at the southern end is completely unknown. Only a single adult 

 from Yosemite Valley on the west slope of the Sierras is known and it 

 could have flown or been blown there from the east side. South of the 

 Sierras, only one adult (from Malibu), and no larvae have been seen 

 from farther west than Gajon Pass in San Bernardino County, although 

 it seems likely it could extend farther west and even northward in the 

 Coast Range since Prunus fasciculata, its favorite host in the Mojave 

 Desert, extends into Santa Barbara and San Luis Obispo counties. 

 No specimens, however, of c. fragile or any other form of M. californicum 

 were found in the area between San Benito County on the north (where 

 M. californicum ambisimile is found) and Los Angeles County on the south, 

 even though there does not appear to be any good reason why some form 

 should not be present. The only species known to occur in that area 

 is M. const ictum. 



The southern distributional limit of c. fragile also is unknown, but 

 no larvae have been collected south of Morongo Valley, San Bernardino 

 County, despite extensive surveys of Riverside and San Diego Counties 

 in both 1960 and 1961. Adults are recorded from Palm Springs, and 

 three males from the Gavilan Hills, near Perris, Riverside County, 

 bear labels indicating they emerged on 27 April 1946, so they were 

 probably collected as larvae. Here again there appears to be no good 

 reason why c. fragile should not be found farther south, since Prunus 

 fremontii, the desert apricot, is quite common and extends into Baja 

 California. This should be an acceptable host, but no specimens have 

 been collected on it to date. 



COMMENTS. — Of all the populations which are given subspecific 

 status in this study, M. californicum fragile is the most different in the 

 most ways from adjoining populations. Intergradation with these 

 populations of M. californicum, however, is so complete in every way 

 that there is no doubt that it has not yet developed the isolating 

 mechanisms necessary to maintain itself as a distinct species. 



Specimens Examined. — 1608 (Museum specimens — 175 males, 143 females, 

 224 larvae; reared specimens — 589 males, 477 females, plus numerous larvae 

 and egg masses). See Appendix I for data on collections made during this 

 study (page 278). 



