CAROTENOIDS 



this. Attention should, however, be drawn to the ladybirds, Coccinella 

 spp., which accumulate lycopene, although it is extremely unlikely 

 that this carotene occurs in their food. A study of the mechanism of 

 formation of lycopene in these insects should be extremely revealing. 



The storage of an individual carotenoid does not imply that others 

 are not absorbed ; they may be absorbed and oxidatively destroyed 

 whilst traversing the intestinal tract. Goodwin ^^ attempted to settle 

 this point in locusts by examining the diet (grass) and faeces of locusts 

 for carotenoids. However, it was found that as so much undigested 

 grass was excreted in the faeces, it was impossible to decide whether 

 carotene was preferentially absorbed or not. The same objection 

 undoubtedly applies to accepting the suggestion that the lowered 

 xanthophylls : carotenes ratio in B. mori faeces compared with that 

 of its diet, implies preferential destruction of xanthophylls in the 

 lumen. ^ ^ 



It seems certain that insect carotenoids are of alimentar}^ origin for 

 on a carotenoid-free diet neither Tineola biseliella,^^ Tenebrio molitor^'' 

 nor Blatella germanica^^ produces carotene, and Chauvin** has 

 produced some evidence suggesting that Schistocerca carotenoids 

 are reduced on a low carotenoid diet. The work of Przibram and 

 Lederer^' on the green Mantis Sphodromantis bioculata, should be 

 repeated for, if it be tru&, it is the only known example of animals 

 producing carotenoids de novo. It will be recalled that Przibram and 

 Lederer claimed that the green varieties, bred for colourless eggs and 

 maintained on a carotenoid-free diet, always contained carotenoids. 



FUNCTION 



No specific function has been assigned to insect carotenoids. The 

 accumulation of astaxanthin in the eyes of Schistocerca and Locusta 

 suggests that it may play a part in photoreception, for in other lower 

 animals from which vitamin A is absent astaxanthin undoubtedly 

 functions in this way. 



There is a sexual differentiation in carotenoid disposition in some 

 insects ; the bright yellow of female B. mori compared with the white- 

 ness of the male, is due to carotenoid deposition, but the difference be- 

 tween the colour of male and female haemolymph in Pieris brassicae is, 

 however, not due to different carotenoid concentration but to different 

 amounts of protein ** oxidation products " ^ No sex-differences have 

 been noted in the total amounts of carotenoids present in Locusta and 

 Schistocerca^ but in mature males some [3 -carotene migrates from the 

 fatty tissues into the cuticle and this is mainly the cause of the yellow 

 colour which the mature males assume ^^ {see also p. 221). 



224 



