COLOR AND COLORATION l6l 



(Tower.) Thus in Leptinotarsa decemli'neata the pattern "is composed 

 of a dark cuticular pigment upon a yellow hypodermal background." 



Combination Colors. The splendid changeable hues of Apatura, 

 Euplcea and other tropical butterflies depend upon the fact that their 

 scales are both pigmented and striated. Under the microscope, certain 

 Apatura scales are brown by transmitted light and violet by reflected 

 light, and to the unaided eye the color of the wing is either brown or 

 violet, according as the light is received respectively from the pigment 

 or from the striated surfaces of the scales. According to Tower, chemico- 

 physical colors "which are of exceedingly wide occurrence, are also the 

 most brilliant and varied of all those found in insects. To this class be- 

 long all metallic iridescent, pearly, and translucent colors, as well as blue, 

 green, and violet in almost every case." 



Nature of Pigments. Some pigments are taken bodily from the 

 food; others are manufactured indirectly from the food, and some of 

 these are excretory products. 



The green color of many caterpillars and grasshoppers is due to chloro- 

 phyll, which tinges the blood and shows through the transparent integu- 

 ment. Mayer has found that scales of Lepidoptera contain only blood 

 while the pigment is forming; that the first color to appear upon the pupal 

 wings is a dull ochre or drab the same color that the blood assumes when 

 it is removed from the pupa and exposed to the air; also that pigments 

 like those of the wings may be manufactured artificially from pupal 

 blood. Pieridae are peculiar in the nature of their pigments, as Hopkins 

 has shown. The white pigment of this family is uric acid and the reds 

 and yellows of Pieris, Colias and Papilio are due to derivatives of uric 

 acid; the yellow pigment, termed lepidotic acid, precedes the red in time 

 of appearance, the latter being probably a derivative of the former. The 

 green pigments of some Papilionidae, Noctuidae, Geometridae and Sphin- 

 gidae are also said by some investigators to be products of uric acid, which 

 in insects as in other animals is primarily an excretory, or waste, product. 



Effects of Food on Color. Besides chlorophyll, to which various 

 caterpillars, aphids and other forms owe their green color, the yellow con- 

 stituent of chlorophyll, namely xanthophyll, frequently imparts its color 

 to plant-eating insects, while some phytophagous species are dull yellow 

 or brown from the presence of tannin, taken from the food plant. Most 

 pigments, however, are elaborated from the food by chemical processes 

 that are not well understood. 



Many who have reared Lepidoptera extensively know that the color 

 of the imago is influenced by the character of the larval food, other con- 



