REVISION IVIALACOSOMA HUBNER IN NORTH AMERICA 43 



For lack of a better term it is called the "cement layer" here, since this 

 term currently is widely used. 



Much of the cement layer can be removed by careful scraping. This 

 greatly reduces the intensity of the blue. The intensity is affected also 

 by the microtrichia, with the most intense blues occurring in those 

 areas where the microtrichia are most heavily pigmented and most 

 tightly packed (resulting in a blacker background). Less heavily 

 pigmented and/or more widely spaced microtrichia in combination 

 with the colored fat body result in lighter blues, blue-grays, ofT-whites, 

 etc. 



On larvae of M. americanum (fig. 350), the white dorsal stripe is the 

 result of a white fat body and nearly colorless microtrichia which are 

 covered with a white cement layer. The properties of this layer which 

 make it appear white rather than blue are unknown, but it appears 

 to be somewhat thicker than the blue layers, and it is deposited on a 

 white background instead of black. There could also be differences in 

 the composition or deposition of it which could influence the color. 

 Black microtrichia surround the bases of numerous secondary setae 

 located on the dorsal stripe, but the cement layer does not cover these 

 areas, so they are seen as black. The small orange sinuous areas beside 

 the dorsal white stripe appear to be covered with colorless microtrichia 

 and a coloiless cement layer, but the orange fat body showing through 

 from below seems to dominate completely all other colors. 



From this brief description of the major components of the color 

 pattern and their location in Malacosoma, it can be seen that the 

 larval color pattern is the result of many variable factors interacting 

 in a complex way, and that the color pattern could be greatly altered 

 by relatively minor changes in the components. For example, if the 

 cement layer were deposited over greater areas of black microtrichia, 

 the amount of blue would be increased and the black decreased. 

 Nothing is known about the factors which influence the development 

 of color pattern in Malacosoma larvae. 



To describe the color patterns of all species and their variations, 

 the following terminology has been adopted for the diff"erent areas 

 and for certain distinctive marks. The body is divided into six longi- 

 tudinal areas as indicated in figure 7. These are the middorsal, ad- 

 dorsal, subdorsal, supraspiracular, subspiracular, and ventral areas. 

 These areas are not exactly the same as those used by Crumb (1929) 

 and others in describing the color patterns of lepidopterous larvae, but 

 the color patterns of Malacosoma are not exactly the same, so a modified 

 system had to be used. 



In addition to the six basic areas, the "dorsal stripe" is referred to 

 at various times. This stripe is always white or bluish-white, straddles 



279-280—68 i 



