128 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



not be expected to do well if introduced. Neveitheless, they should be 

 able to survive in some areas, especially at certain elevations in the 

 mountains. They may have become temporarily established on several 

 occasions, and they may presently exist at some of the listed localities 

 or others, but we are not aware of any authentic reports of them from 

 Southern California. Therefore, any reports of large tents should be 

 investigated to determine if they are M. calif ornicum fragile, the only 

 tentbuilder which is certain to be native to parts of Southern California, 

 or whether they are some other subspecies or population of calif ornicum 

 that has been introduced from non-Southern California localities. 



ECONOMIC IMPORTANCE.— iW. calif ornicum including its sub- 

 species has caused heavy defoliation of many different hosts in many 

 areas, but most of its hosts are scrubby species of little commercial 

 value. The most serious damage to date is probably that reported by 

 Clark (1956a) in which defoliation in combination with other factors 

 has resulted in the death of bitterbrush, Purshia tridentata, in parts of 

 northeastern California, and its replacement by less desirable species. 

 Purshia tridentata is a valuable browse species for both domestic stock 

 and wild game. Possibly the defoliation of aspen in the southern Rocky 

 Mountains should also be regarded as serious, but throughout most of 

 its range calif ornicum will have to be classified along with americanum and 

 incurvum as more of a nuisance than a serious pest. 



COMMENTS. — Both males and females of M. californicum and its 

 subspecies can be divided into two large groups which differ from each 

 other in a single genitalic character. These differences, however, inter- 

 grade between groups, and individuals of one group having characters 

 which more closely fit the other group may be found. 



The first group is composed of californicum ambisimile, californicum 

 californicum, californicum recenseo, californicum pluviale, the Mendocino- 

 Trinity population of M. californicum, and other populations of califor- 

 nicum found along the Pacific coast. This group is called the north- 

 western group. The second group is composed of californicum lutescens, 

 calif ornicum fragile, and the remaining central populations of M. califor- 

 nicum. This group is called the southeastern group. 



Males of the northwestern group (figs. 19-23) usually have the 

 prongs of the accessory claspers closer together than do males of the 

 southeastern group (figs. 24-26), but some specimens in both groups 

 are more or less intermediate (figs. 20 and 26). Females of the north- 

 western group (figs. 91 and 97-99) usually have the dorsal lobe of the 

 ovipositor reduced, while females of the southeastern group (figs. 100- 

 102) usually have more distinct dorsal lobes, but some specimens of 

 both groups are more or less intermediate (figs. 91 and 101). 



