REVISION ]VIALACOSOMA HUBNER IN NORTH AMERICA 119 



La Sal Mountains in San Juan County, and 10 miles west of Huntington 

 in Emery County. Both species were found in Arizona, but not at the 

 same locality. Those populations of incurvum found in central and 

 southern Arizona are named Ai. incurvum incurvum (fig. 4), and those 

 centered in southern Utah are named M. incurvum discolor atum (fig. 4). 

 The populations of M. californicum found in southwestern Utah and 

 northwestern Arizona are called M. californicum fragile (fig. 2), and 

 those found in the remainder of Utah and Arizona are called M. 

 californicum (central populations) (fig. 2). 



The egg masses of i. discoloratum differ from those of californicum 

 which were found at the same locality. Those of i. discoloratum (similar 

 to fig. 117) are covered with nearly white spumaline which contains 

 many small bubbles and no microscopic "specks." Those of californicum 

 are covered with grayish spumaline which contains bubbles of various 

 sizes and also possesses numerous minute dark "specks" (fig. 118) 

 scattered throughout the spumaline. (See the introductory section on 

 egg masses for a discussion of these "specks" and their occurrence in 

 various populations and subspecies of M. californicum, page 21). 



No completely reliable dififerences for separating the larvae of 

 californicum from incurvum are known, but larvae of incurvum discoloratum 

 usually can be distinguished from those populations of californicum 

 or californicum fragile found in the same locality by the characters given 

 in the larval diagnosis iov discoloratum (page 179). Some larvae of both 

 species fall within the range of variation found in the other species 

 and cannot be positively identified. 



The adults do not differ structurally as far as is known, but male 

 incurvum discoloratum usually can be separated by their color pattern 

 from californicum fragile and californicum. Females are nearly impossible 

 to separate, but see the adult diagnosis for incurvum discoloratum for a 

 discussion of both males and females (page 178). 



In 1961 along the Virgin and Santa Clara Rivers i. discoloratum 

 occurred primarily on Populus fremontii, the southwestern Cottonwood, 

 although it also was found on ornamental poplars and rarely on fruit 

 trees. M. californicum fragile occurred on Prunus fasciculata, the desert 

 almond, and on fruit trees. At several places colonies of i. discoloratum 

 were found on small cottonwood trees and tents of c. fragile were found 

 on desert almond growing immediately beneath the cottonwood trees. 

 In every case the c. fragile larvae were much further along in their 

 development than the i. discoloratum lan^ae. 



For example, at one site near Shivwits, Washington County, Utah, the 

 c. fragile larvae were nearly mature, but the i. discoloratum larvae were 

 only about halfway through the penultimate instar. Adult emergence 

 dates for pinned adults which were reared from both of these popula- 



