134 UNITED STATES NATIONAL MUSEUM BULLETIN 276 



would have to be made before any absolute statements can be made 

 concerning the differences between these populations, but from the 

 little that is known it is apparent that the B's are nearly identical to 

 the A's, and should be regarded as the same population. It is also 

 apparent that the BS's are different from the A's and B's in some 

 respects, and they are regarded as a different, although closely related 

 population of the same species. 



This brings up the question of how these populations are related to 

 other populations of calif ornicum. The BS populations are no doubt 

 continuous with similar BS populations found at lower elevations and 

 which are known to intergrade with other neighboring populations of 

 californicum, some of which have specks and some which do not. The 

 relationship of the A populations is not as obvious, but the occurrence 

 of the virtually identical B populations on brush species in the same 

 locality as the A's suggests that the A's are related through the B's to 

 other populations without specks which occur on brush. 



When many different characteristics are considered in comparing 

 neighboring populations of calijornicum in Utah and Arizona, it must 

 be concluded that the populations which most closely resemble the A's 

 are those populations of calijornicum without specks which occur on 

 various species of brush. These populations probably intergrade with 

 the A's through the B's. They also intergrade with other populations 

 of calijornicum, including those which have specks, so it can be seen 

 that the A and B populations are linked with the BS populations through 

 intermediate populations which occur at lower elevations, even though 

 direct gene exchange between the A's and BS's is probably reduced 

 where they occur together at higher elevations. If any exchange does 

 take place, it may be in only one direction (from the A's to the BS's) 

 since egg masses containing specks have never been found on aspen to 

 date. (Assuming the presence of specks is an inherited character, and 

 not influenced by the host. This remains to be determined.) 



Possible Relationships Between the Aspen Populations of 



Malacosoma californicum and Populations of 



Malacosoma incurvum 



Previously it was pointed out that incurvum and calijornicum are closely 

 related species which cannot be separated from each other in every case 

 by any known character of any life stage. In some respects the aspen 

 populations of calijornicum are very close to incurvum, but in others they 

 are quite different. Egg masses of both do not have specks, but the 

 spumaline of the A's is tan to brown, while that of incurvum is usually 

 whitish, but may be dark brown in some populations. The spumaline 



