CAROT1NOIDS L\ INVKlfTI-:ili:.\TI>^ 155 



Carotinoids in Insects 



Zoologists recognize as many as eleven different orders of the 

 In-sectia, and state that a million species more or less may exist in 

 the world. When these figures are contrasted with the fact that not 

 over thirty-five or forty species, belonging to four orders, have been 

 examined, with reasonable indications, of carotinoids or closely related 

 pigments being present, it is seen that very little, indeed, has been 

 done in this field. 



The insect orders in which carotinoids appear to be present are the 

 Lepidoptera (butterflies), Rhynchota (bugs), Coleoptera (beetles) 

 and the Orthoptera (locusts, grasshoppers). 



Lepidoptera. In the butterflies themselves the brilliant wing colors 

 are not due to carotinoids, as already mentioned. There are undoubt- 

 edly some color effects which are purely structural, but the red, orange, 

 and yellow pigments appear to be derivatives of uric acid, as shown 

 by the investigations of Hopkins (1889, 1891, 1892, 1896) and Urech 

 (1893). In the larvae and pupa?, however, either carotinoids or 

 modified carotinoids are frequently encountered. 



Medola (1873) first showed that the green color of insects is not 

 due merely to the green digestive mass in the food canal, but to a 

 true absorption of pigment by the hamolymph (blood) of the animals, 

 although in a somewhat modified form. This laid the foundation for 

 the classic experiments of Poulton (1885) on the pigments of the 

 larvae and pupae of a number of species of butterflies. Poulton dis- 

 tinguished between two kinds of pigments in phytophagus larva-, 

 namely, those derived from the food and those produced by the ani- 

 mals themselves. The general thesis which his work supports may 

 perhaps best be explained by the following quotation. "All green 

 coloration is due to chlorophyll; while nearly all yellows are due to 

 xanthophyll. All other colors (including black and white, and some 

 yellow, especially those with an orange tinge) are due to the second 

 class of cause (so far as I am aware: It is, however, extremely prob- 

 able that certain colors may be proved to arise from the modification 

 of the derived pigments, and many observations make it probable that 

 other colors may be derived from plants in the case of larvae feed- 

 ing upon petal?, etc.). The derived pigments often occur dissolved 

 in the blood, or segregated in the subcuticular tissues (probably the 

 hypodermis cells) , or even in the chitinous layer, closely associated 

 with this cuticle itself." 



