176 ENTOMOLOGY 



tives 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, Noctuidse, 

 Geometridae and Sphingidae 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 

 constituent 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- 

 ditions 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 Gregson, Hybernia defolia- 

 ria 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 flowers instead of the leaves of the nettle obtained the 

 variety known as urticoides. Food affects the color of the larva also, 

 as Poulton found in the case of caterpillars of Tryph&na pronuba, all 

 from the same batch of eggs. When fed with only the white midribs 

 of cabbage leaves, the larvae remained almost white for a time, but 

 afterward showed a moderate amount of black pigment; when fed with 

 the yellow etiolated heart-leaves or the dark green external leaves, 

 however, the larvae all became bright green or brown the same pigment 

 being derived indifferently from etiolin (probably the same substance 

 as xanthophyll) or chlorophyll. 



Though the pigments may differ in color or amount according to 

 the kind of food, the color patterns vary without regard to food. Thus 

 Callosamia promethea, Leptinotarsa decemlineata (Colorado potato 

 beetle), Coccinellidae (lady-bird beetles) and a host of other insects 

 exhibit extensive individual variations in coloration under precisely 

 the same food conditions. Caterpillars of the same kind and age are 

 often very differently marked when feeding upon the same plant; for 

 example, Chloridea obsoleta (corn worm) and the sphingid Deilephila 



