PIGMENTARY COLOURS 183 



Pigmentary Colours 



Pigmentary colours in insects are of a diverse character and 

 belong to very different groups exhibiting differences of origin and 

 of chemical constitution. It is not intended here to enter into 

 a detailed discussion of their nature and properties from the 

 biochemical standpoint, but to refer to advances in knowledge of 

 the more important pigments, and mainly from their biological 

 aspect. For this purpose it is convenient to group the pigments 

 of insects into four categories : (1) chlorophyll and other derived 

 pigments ; (2) haemoglobin and allied pigments ; (3) pigments 

 of protein origin ; and (4) pigments with purine bases. This 

 grouping does not include all insect pigments, and certain others, 

 either lesser known or of more restricted occurrence, have been 

 omitted. The general subject of pigments in animals, treated 

 both chemically and biologically, is well summarised by Verne 

 (1926). The reader is referred to this handbook for an elementary 

 treatise on the problems concerned and for a bibliography of their 

 extensive literature. 



1. Chlorophyll and other Derived Pigments. Included under 

 this heading are those pigments which are absorbed from the food 

 without undergoing very marked changes in composition. They 

 are plant pigments which belong chemically to. two very different 

 groups. They include the carotins, anthocyanins and fiavones, 

 which have no nitrogen in their chromogenic nucleus, and the 

 chlorophylls which have a tetrapyrollic nucleus. 



The first impetus given to the study of the fundamental nature 

 of insect pigments is due to Poulton (1893), whose experiments on 

 the colours of Lepidopterous larvae are familiar to entomologists. 

 His work suggests that a modified chlorophyll, derived from 

 plant chlorophyll, and xanthophyll occur in the blood and 

 integument of caterpillars, and form the basis of their prevailing 

 type of coloration. Spectroscopic examination of the blood, when 

 compared with that of an extract of the colouring matter of the 

 food-plant, showed an extremely close similarity in the two cases. 

 Considering the chemical processes to which these pigments are 

 subjected in the passage through the walls of the digestive canal 



