REVISION MALACOSOMA HUBNER EST NORTH AMERICA 129 



These differences certainly are not constant enough to warrant 

 spHtting californicum into two species since the two groups are aUke in 

 many other ways, but the differences may be an indicator of geograph- 

 ical isolation which took place between ancestral populations at some 

 time in the past. 



The six subspecies of M. californicum that are recognized here lie at 

 the periphery of a huge central region (figs. 2 and 3) containing many 

 populations which are highly variable in many characteristics. None 

 of the populations occurring in this central region have been found to 

 be consistently different enough to warrant formal recognition, so they 

 are all referred to as M. californicum. A couple of them, however, are 

 worthy of some additional comments. 



The Mendocino-Trinity Population 



In northern California between the distributional ranges of M. 

 californicum californicum on the south (fig. 3) and M. californicum pluviale 

 on the north (fig. 2) is found a highly variable population of calif ornicum 

 which has never been formally named, but was called Malacosoma sp. 

 by Langston (1957). Colonies are commonly found on Quercus agrifolia, 

 Cercocarpus betuloides, Ceanothus spp., Salix spp., and fruit trees, but may 

 be found on other hosts, too. Egg masses, tents, and adults are the same 

 as those of nearby populations of californicum, except that adult males 

 are often more variable and the dominant color of those reared from 

 single colonies may range from yellow to red-brown. 



The major difference between this population and neighboring ones 

 is in the larval color pattern (figs. 358-363), and the variability is 

 nearly as great as that found in the Great Basin and the southern Rocky 

 Mountains. The most striking feature is the frequent presence of exten- 

 sive lateral blue areas and the occurrence of white secondary lateral 

 setae on many specimens (figs. 362 and 363). The closest populations 

 of californicum which possess either of these characteristics are M. 

 californicum ambisimile in the Santa Cruz Mountains (figs. 354 and 355), 

 and populations of M. californicum and M. californicum fragile (figs. 366 

 and 367) which occur east of the Cascades and the Sierra Nevada. 

 Neither of these characters, however, nor any others were found to be 

 constant enough to warrant recognition of this population as a sub- 

 species. It is referred to, therefore, as the Mendocino-Trinity 

 population of A/, californicum. It may be a remnant of the original stock 

 which gave rise to the other Pacific Coast subspecies oi calif ornicum since 

 it seems to possess all of the characteristics which they possess, and more. 



