REVISION MALACOSOMA HUBNER IN NORTH AMERICA 1]3 



even, niiddorsal stripe, bordered by an area of longitudinal reddish- 

 brown and black wavy lines which cover the addorsal area. Setal group 

 Dl usually surrounded by an irregular black spot. Subdorsal area with 

 a central black area on each segment crossed by a vertical blue mark 

 posteriorly, and a less striking, more variable blue patch anteriorly; 

 setal group SD at ventral edge of central black area. Dorsal edge of 

 supraspiracular area marked with an irregular, discontinuous, reddish- 

 brown to yellowish, longitudinal, wavy line forming a ventral border 

 for the central black area; remainder of supraspiracular area and sub- 

 spiracular area variably mottled and finely streaked with black, reddish- 

 brown, blue, blue-gray, yellow and white. Ventral area mottled gray 

 and black, each segment with a median transverse black band. Primary 

 and secondary dorsal setae reddish-brown to orange or yellow; lateral 

 setae reddish-brown to orange or white. 



LARVAL DIAGNOSIS. — Larvae of americanum can always be iden- 

 tified by the apparently continuous, even, yellow-white middorsal stripe. 

 No other North American larva is marked like this. Within its distribu- 

 tional area the only larvae that could possibly be confused with ameri- 

 canum are some individuals of M. californicwn lutescens which may have a 

 narrow middorsal stripe that appears to be nearly continuous as in 

 figure 376 (usually the middorsal stripe is definitely broken as in figures 

 373-375). Confusion between these two has probably taken place in 

 the past and resulted in americanum being reported from the western 

 Great Plains. However, americanum larvae have black heads, and c. 

 lutescens larvae have predominantly blue heads mottled with black. In 

 addition, the lateral areas of c. lutescens are largely blue, and there is no 

 central black subdorsal area crossed by a posterior vertical blue line as 

 in americanum, although c. lutescens may have a conspicuous vertical black 

 bar as in figures 375 and 376. These characters are most distinct in 

 late instar larvae, and it may be difficult to positively identify early 

 instars by them. 



Possibly the best characters for separating early instar americanum from 

 c. lutescens are the distinctly undulating, longitudinal yellowish line just 

 below setal group SD, and the central, black subdorsal area which 

 includes setal group Dl and is divided by a longitudinal yellowish line 

 on americanum. These characters are most clearly visible on preserved 

 or wetted specimens where blue colors do not show. Aialacosoma c. 

 lutescens has a similar longitudinal line just below setal group SD, but 

 it is usually less distinct and without strong undulations; the subdorsal 

 area may have a central black area, but this usually takes the shape of 

 the vertical black bar, and it is never divided longitudinally by a 

 yellowish line. 



