62 UNITED STATES NATIONAL MUSEUM BULLETIN 276 



not possible to compare developmental rates under field conditions 

 in 1960, since the closest populations that were located of these two 

 forms were nearly 100 miles apart. 



Figure 2 shows numerous localities for lutescens in Canada, and rela- 

 tively few in the United States, but this is an indication of the intensity 

 of collecting rather than abundance, since the Forest Biology Labora- 

 tories in Canada have been surveying Canada for many years, and 

 practically nothing has been done in the United States. Even so, 

 there is a notable lack of collections from the area near the black line 

 separating the lutescens localities from the pluviale localities in Alberta, 

 Saskatchewan, and Manitoba. This may be due to the lack of roads 

 in much of the area, resulting in fewer collections, or possibly lutescens 

 and pluviale are so well adapted to their respective areas that neither 

 they nor their "hybrids" do well in the boundary area. 



The caterpillars reared from egg masses R27, R36, and their recip- 

 rocals were intermediate between the parent populations in many 

 aspects of the color pattern, but they showed greater variability than 

 either of the parent populations, although lutescens normally is more 

 variable than pluviale. Nearly all of the hybrids showed a distinct 

 vertical black bar which always is present on pluviale, but frequently 

 absent on lutescens from the northern prairies. The lateral blue area, 

 so pronounced in lutescens but reduced to patches of blue at the anterior 

 and posterior subdorsal spots in pluviale, was quite variable, but more 

 often than not it was more extensive in the hybrids than in pluviale. 

 The dorsal stripe was always bluish-white as in both parents, but its 

 width was variable. In the parents the width of the dorsal stripe is 

 nearly always greater in pluviale. The addorsal area, which is largely 

 black in lutescens, and orange with some black in pluviale, was variable 

 with most of the specimens falling between the parental extremes. 



The great majority of the adult male hybrids were similar in color 

 and pattern to those oi pluviale, with an occasional one tending toward 

 lutescens. Most of the females, on the contrary, were intermediate in 

 color and pattern, with some specimens tending more toward lutescens. 



Many (but not all) male pluviale can be separated from lutescens by a 

 character of the prongs of the accessory claspers (compare figs. 22 and 

 23 with 24 and 25). Figures 23 and 24 represent the extremes, and 

 most specimens are closer to figures 22 or 25. Many female pluviale can 

 be separated from lutescens by the larger and more distinct dorsal lobe 

 of the ovipositor (compare figs. 98 and 101). These figures are close 

 to that which would be considered "normal." See the comments under 

 M. californicum (Packard) for a more detailed discussion of these 

 characters (page 128). 



