REVISION MALACOSOMA HUBNER IN NORTH AMERICA 23 



larvae feeding on a certain host species or closely related group of 

 hosts, such a diversit)^ would not be expected. Furthermore, if the host 

 were the only controlling factor in the production of specks, one would 

 not expect to find specks in the spumaline of some populations feeding 

 on a given host, and no specks in other populations feeding on the 

 same host. Yet this is what is found when an examination is made of 

 populations feeding on a widely distributed host, such as Prunus 

 virginiana. 



The biochemistry of these specks and of the diffuse color in the 

 spumaline is not known. It is possible that the two are chemically 

 similar, and are concentrated and diffuse pigment of the same type. 

 The specks are most easily obsei-ved in populations of M. californicum 

 fragile which occur in the Mojave Desert. The color of the spumaline 

 of these populations is a light gray. Neighboring populations of M. 

 californicum have spumaline which is brownish-gray or brown, and the 

 specks are more difficult to see because of the more heavily pigmented 

 spum-aline. Specks, however, often appear to be as numerous in the 

 brown spumaline as they are in the gray spumaline of the desert 

 populations of c. fragile, so it cannot be assumed that the specks are 

 simply due to a failure of the pigment to disperse evenly throughout the 

 spumaline. 



If the production of specks is either a normal stage of development 

 of spumaline pigment or a concentration of some excess precursors, then 

 one might expect to find an occasional egg mass of the other species in 

 which specks were present. None have ever been found in the spumaline 

 of species other than M. californicum, so it is reasonable to conclude 

 that the production of specks is a peculiarity of some populations of 

 M. californicum. Whether the specks are a stage in a process or the 

 product of a process remains to be determined. 



Specks have never been found in populations of M. californicum 

 occurring along the Pacific Coast or in the northern United States 

 and Canada. Figure 5 outlines the area within which populations have 

 been found that have at least a few specks in the spumaline of some 

 egg masses. Within this area there are populations that here are 

 regarded as M. californicum which do not have specks. These are more 

 fully discussed in the section on M. californicum. 



The closely related species, A/, incurvum., also occurs partly within 

 this area, but as far as is presently known, all populations of incurvum 

 incurvum, incurvum discolor atum, and incurvum aztecum have spumaline 

 which does not contain any specks. If fact, the lack of specks is one of 

 the best ways to separate incurvum egg masses from those of californicum 

 when both species are found in the same locality. 



