130 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



Only two collections were made on the west slope of the outer Coast 

 Ranges in northern California (Coll. Nos. 68 and 69). Neither of these 

 could be reared beyond the third instar, and because of this they are 

 called M. californicum and included in the Mendocino-Trinity popula- 

 tion, although it is possible they could be M. californicum pluviale which 

 may extend southward along the Pacific Coast in the fog belt. 



The Aspen Populations 



The most interesting of the Great Basin and Rocky Mountain popu- 

 lations are those which occur on aspen in the southern Rocky Moun- 

 tains. Defoliation of aspen by M. californicum in Arizona, New Mexico, 

 Utah, Colorado, and Wyoming has been reported either in the literature 

 or was observed during this study. M. californicum also has been occasion- 

 ally found on aspen in other parts of the West, but aspen does not seem 

 to be a preferred host in these other areas and heavy defoliation has not 

 been reported, although it must be pointed out that aspen is less exten- 

 sive in these areas and tends to occur in smaller, more isolated patches 

 (Baker, 1925). 



Most of the collections made on aspen during this study were made 

 in Arizona, Utah, and Wyoming but adults collected by Dyar and 

 Caudell in 1902 near Half Way House on Pikes Peak, Colorado, also 

 have been examined. Caudell (1902a) reported that the aspen near 

 Half Way House was completely defoliated, so the adults that he and 

 Dyar collected had been feeding, no doubt, on aspen as larvae. These 

 adults are similar to those which have been reared from aspen in other 

 areas, except for having less reddish-brown in the color pattern. 

 The larvae of tent caterpillars, which in recent years have defoliated 

 aspen in southern Colorado and northern New Mexico, are similar 

 to larvae collected on aspen in northern Arizona and southern Utah, 

 and are regarded as the same. No egg masses or reared adults of these 

 populations have been available, but adults collected at high elevations 

 in other parts of New Mexico are similar to those from Arizona and 

 Utah except that they are not as reddish or orange-brown. 



One characteristic that is common to all of the aspen populations is 

 the complete lack of any specks in the spumaline of any egg masses 

 collected from aspen or in the spumaline of unspent females of these 

 populations. (See the section on egg masses for a discussion of the 

 specks (page 20), and figvire 5 for a map of the area within which 

 populations containing specks in their spumaline may be found.) 



In southern Arizona in the Chiricahua Mountains egg masses found 

 on aspen (Coll. 246) contained no specks and the spumaline was the 



