140 COI.ORATION IN I^EJPTINOTARSA. 



HYPODERMAI, COI.ORS. 



The hypodermal colors in this genus are red, orange-red, orange, yellow, 

 pale yellow, and pale yellow-white. Of these the reds, yellows, and pale yel- 

 low-whites are most permanent, but all fade on exposure to light, with age, or 

 at death. They are products of the metabolism of the hypodermal cells, in 

 the ectodermal portions of which they exist as granules, and serve as a back- 

 ground for the pattern formed by the cuticula colors. They are practically 

 the same over the entire animal, only rarely exhibiting local variations. They 

 are permanent throughout life, persisting through larva and pupa into the 

 imago, where they form the lighter portion of the color pattern. 



CHEMICAI, EXAMINATION OF THE HYPODERMAL COLORS. 



The chief hypodermal colors are yellows and reds, or combinations thereof. 

 They exist as granules in the hypodermal cells of the larva, pupa, and imago. 



If an elytron of decemlineata be taken a day or two after emergence, when 

 it is of a yellow color, and treated with dilute acid, the yellow become orange- 

 yellow, orange, orange-red, and then red, and this color is made permanent 

 if the wing be washed free of acid and dried. Alkalis, on the contrary, reduce 

 this red to a yellow, and further reduce the yellow to a colorless or whitish 

 condition, from which it is not possible for it to regain the original yellow. 

 Portions of the integument of rubicunda, which has a bright red color in life, 

 are changed to yellow by alkali and to pale yellow-white if the treatment is 

 continued ; but if they are washed and soaked in dilute HCl the red color is 

 permanently restored. With rubiginosa like results may be obtained. If 

 integument from undecimlineata be treated with acids, a progressive series 

 of changes from the normal pale yellow-white to a wine-red color follows, 

 and the reverse series accompanies treatment in alkalis. These changes can 

 be repeated several times in the same specimen. 



Color reactions like these have been described by Coste and Urech in the 

 scales of Lepidoptera, and by Zopf and others in Coccinellidse. Zopf has 

 shown that these colors in Coccinellidae are lipochromes; and the red and 

 yellow alternatives found in Leptinotarsas suggest that these are the same. 



All of the hypodermal colors are easily soluble when treated in alcohol or 

 ether, and often in water, giving solutions which on concentration by evapo- 

 ration have the color of the insect treated. Acids and bases produce with 

 these solutions progressive and regressive color changes as described above. 

 I have also made with them repeated tests for azo pigments, but no trace has 

 been detected, and I hold that they are in no way related to azo colors, as is 

 claimed by Enteman. 



Tests for the presence of lipochromes with Soudan III and like reagents 

 show decided reactions indicating the presence of fatty pigments of the lipo- 

 chrome series. 



