82 VARIATION IN LEPTINOTARSA. 



TabIvE 27. — Variation in color of elytra in L. haldemani, L. lihatrix, and L. violescens. 



Species. 



Class. 



Remarks. 



I 



2 



3 



4 



i 



5 6 



7 



L haldemaui 







2 



3 



8 



5 

 . . . 



68 22 

 6 82 



I 5 



i 



4 

 94 



N. = 500 individuals. 

 N. ^ 200 individuals. 

 N. = 100 individuals. 



L. libatrix. 



L. violescens. . . . 







Variations in the elytra of other groups. — The beetles in these groups 

 comprise species of which I have not been able to obtain a sufficient num- 

 ber for quantitative study, but which, nevertheless, present interesting and 

 suggestive color-pattern conditions. In these species the pattern consists 

 largely of bands, stripes being almost entirely wanting. When stripes do 

 exist they are made up of the coalesced anal, cubital, and often medial stripes, 

 and are found only along the anal edge of the elytron. These coalesced 

 stripes are compressed into a narrow sutural line of dark color, from which 

 bands extend across the wing (plate 14, figs. 49 to 57). These figures explain 

 themselves and show clearly the way in which the color pattern of bands of 

 dark color, bands connected by longitudinal stripes, and spots of hypodermal 

 color on a dark background are produced by the development of the band and 

 stripes, or both. In plate 14, figs. 55 to 57, are shown, in L. lacerata, the 

 transition from a pure banded condition to one in which the bands are con- 

 nected by the partial development of certain of the stripes ; and finally by the 

 further coalescing of bands and stripes, is shown the production of a pattern 

 with light spots. In L. pudica (plate 14, figs. 53 and 54) we see the opposite 

 process in the formation of black spots on a light background by a reduction 

 of the bands, which leave spots at the points of crossing of the bands and 

 stripes. In L. zetterstedti is shown much the same process at work. 



The color patterns of the elytra of the genus Leptinotarsa show certain 

 important and interesting phenomena. The rarity of abmodal cases and 

 of sports, or extreme variations, is striking. Where these exist they are 

 limited entirely to certain species of the lineata group. The variations are 

 almost always continuous and fall in every instance about a single modal con- 

 dition which is, as far as the evidence goes, constant for the character and 

 species. We shall see later that the modes of the different species A^ary geo- 

 graphically and from year to year, but the modes for the entire species seem 

 to be a constant quantity. 



By far the most interesting phenomenon exhibited by the color patterns of 

 the elytra in these beetles is the rigid directing of variation along certain well- 

 defined lines. In no species is there the slightest evidence of promiscuous or 

 indeterminate variation. 



