196 ENTOMOLOGY 



the transparent integument. 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 artifi- 

 cially 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 Pier is. 

 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, Noctu- 

 idse, Geometridae and Sphingidse are also said by some inves- 

 tigators 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 constituent of chlorophyll, namely xantho- 

 phyll, 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 pig- 

 ments, 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 conditions being equal, and are able at will 

 to effect certain color changes simply by feeding the larvae 

 from birth upon particular kinds of plants. In this country 

 we have few observations upon the subject, but in Europe 

 the effects of food upon coloration have been ascertained in 

 the case of many species of Lepidoptera. According to Greg- 

 son, Hybernia defoliaria is richly colored when fed upon 

 birch,' but is dull colored and almost unmarked when fed on 

 elm. Pictet, by feeding larvae of Vanessa urticce on the flow- 

 ers instead of the leaves of the nettle obtained the variety 



