REVISION MALACOSOMA HUBNER IN NORTH AMERICA 179 



of other populations of M. calif ornicum usually are more orange-brown 

 with more sharply contrasting lines on the forewings, but otherwise are 

 closely similar to female i. discolor atum. Other species such as M. tigris 

 and M. disstria which might be collected in the same area can be sep- 

 arated by the diagnostic characters given for them (pages 103 and 86). 



MATURE LARVAE (figs. 395-399).— Head blue, mottled with 

 black, sparsely covered with fine white to yellowish setae. Middorsal 

 area usually with some sort of stripe (figs. 395-398), but very rarely 

 entirely black (fig. 399). Stripe varying from a few narrow bluish- 

 white dashes to a slightly broken, middorsal bluish line that is often 

 about same shade of blue as subdorsal area. Addorsal area varying 

 from black to orange, but usually a mixture of both, with the black 

 sometimes reduced to only a black spot around setal group Dl as in 

 figure 395, but never entirely absent. Area around setal group D2 

 often visible as a small black spot (fig. 395). Subdorsal area bluish, 

 speckled with fine black dots around bases of secondary setae. Sub- 

 dorsal line, if present, consisting of only a pale yellowish mark on each 

 segment immediately ventral to a variable black area surrounding 

 setal grovip SD, Specimens have never been seen with a vertical black 

 bar connecting setal groups Dl and SD, as is often the case in many 

 populations of M. californicum. Supraspiracular area usually slightly 

 darker, more grayish-blue than subdorsal area, and also speckled with 

 black dots around bases of secondary setae. Subspiracular area various 

 shades of pale bluish-gray white. Ventral area blackish, often mottled 

 with gray-white, and generally with a black median spot or band on 

 each segment, which is most conspicuous on lighter specimens. Primary 

 dorsal setae yellowish to whitish to orange; secondary dorsal setae 

 orange. Primary and secondary lateral setae usually white, occasionally 

 somewhat yellowish, rarely the primary setae are somewhat dark. 

 Lateral setae not tufted or only slightly so. 



LARVAL DIAGNOSIS. — Larvae are difficult to separate from 

 those of A/, calif ornicum fragile and other populations of Af. californicum. 

 There are no good characters which will positively identify them, but 

 locality and host data will help, since i. discoloratum seems to show a 

 decided preference for Cottonwood while californicum fragile and 

 californicum prefer various shrubs. Some californicum larvae have a 

 vertical black bar which i. discoloratum does not have, but c. fragile 

 does not have one in the areas where it occurs with i. discoloratum. 

 Fragile larvae, however, usually have a distinct, black, dorsal, 

 longitudinal band (figs. 380-382) which contains a few inconspicuous 

 orange markings at the most, and c. fragile almost always has a con- 

 spicuous middorsal broken blue-white line. Larvae of i. discoloratum 

 generally have some dorsal black, which may be reduced to a black 



