222 



COLORATION IN LEPTINOTARSA. 



THE EVOLUTION OF COLORATION. 



One of the most conspicuous traits of the genus Leptinotarsa is the devel- 

 opment of its specific characters along definite lines, and not in all directions. 



Upon the elytra of Leptinotarsa the color pattern is composed of stripes, 

 spots, or bands, or combinations thereof. The stripes are color marks parallel 

 to and between the veins, the bands cross the veins at right angles, while the 

 spots usually lie between the veins, or sometimes over them. These elytral 

 color patterns are represented in table 101, where the number of species 

 characterized by the different patterns is also shown. 



Table ioi. Different types of color pattern in the elytra of Leptinotarsa, and 

 the number of species which exhibit them. 



It is apparent in this table that among the 43 species in the genus, 16 have 

 an elytral color pattern which consists solely of stripes, and 4 have a pattern of 

 both stripes and spots, in which the stripes are dominant. Therefore, the pre- 

 vailing element in the coloration is the stripe, 20 species in the genus having 

 striped elytral patterns and the remainder unicolorous, spotted or banded. From 

 the table it is also evident that there are four directions of elytral color-pattern 

 evolution in the genus first, toward a unicolorous condition (9 species) ; sec- 

 ond, toward a striped condition (20 species) ; spotted (8 species), and banded 

 (6 species). If we compare the table with the groups of the genus outlined 

 in the first paper we find that the flavopustulata group is made up of spotted 

 or banded-striped species ; the haldemani group of striped and dark unicolor- 

 ous species ; the lacerata group of spotted, banded, banded-striped, and dark 

 unicolorous species; the rubiginosa group of light unicolorous species; the 

 lincata group of striped or light unicolorous species, and the dilccta group of 

 striped, striped-spotted, or spotted species. The most casual inspection of 

 plates 22 and 23, where the color patterns of the genus are represented, 

 will at once reveal the fact that the four types of color pattern are really due 

 to the combinations possible between the two systems described in the section 

 on color ontogeny, namely, stripes or bands, the spots resulting simply from 

 the breaking up of the two other elements. 



In the second chapter it is shown that the variation of the color pattern 

 follows along definite lines, and later, in the discussion of color ontogeny, 

 that color first develops between the veins, and crosses them at five definite 

 points; and when it fails to develop it is lost first at certain regions or 



