188 THE FUNDAMENTAL ASPECT OF COLORATION 



Tritogenaphis rudheckice Palmer and Knight (1924b) found that 

 the chief red pigment present is not soluble in fat solvents, but 

 is readily extracted by water or cold methyl-alcohol, yielding 

 vermilion-coloured solutions. The properties of this pigment, 

 as determined by them, are strongly suggestive of its being an 

 anthocyanin. Small quantities of carotin were also detected, 

 but were insufficient to have any real influence upon the general 

 coloration of the insect. It is noteworthy that Glaser (1917) had 

 previously shown that another aphid, viz., Pterocomma smithice, 

 which feeds upon willow, contains a red pigment which is 

 apparently located in the fat-body. From preliminary tests 

 Glaser concluded that the colouring matter appeared to be of the 

 nature of an anthocyanin. Since, however, no anthocyanin could 

 be detected in the shoots of the food-plant, he suggested that the 

 aphid absorbs hydroxyflavones along with the sap, and that these 

 become reduced to anthocyanin in the body of the aphid, and 

 ultimately converted into the red pigment. 



Pigments of the flavone group have also been recently detected 

 in insects, and, according to Palmer and Knight (1924b), a red 

 colouring material obtained from the Coreid bug Leptocoris 

 trivitatus is of this nature. They also obtained a similar pigment 

 from other Hemiptera belonging to the families Capsidae, Lygaeidse 

 and Reduviidae. As to the origin of the flavone-like pigment in 

 these cases, it is presumed that it is derived from the food-plants, 

 but they did not pursue this subject further. In the Reduviidae, 

 which are predators, it would appear that the pigment would either 

 have to be derived indirectly through some plant-feeding prey, or 

 be synthesised by the insects themselves. More recently Thompson 

 (1926) has provided evidence that insect pigments of the nature 

 of flavones or flavonols are derived from the food-plant. In the 

 Marbled White butterfly (Melanargia galatea) a small amount of 

 a yellowish pigment is present in the wings, and gives no reaction 

 or spectrum, which supports the assumption that it is a carotinoid. 

 On the other hand, its properties ally it with a flavone. He was 

 able to show further that an identical pigment is present, both 

 free and in glucosidic combination, in cocksfoot grass {Dactylis 

 glomerata) which is one of the known food-plants of the larva of 



