| Summary: | The difficulty of obtaining accurate and comparable measurements of the carotenoid content of plant and insect specimens is discussed. The carotenoids present in cabbage and in all stages in the life cycle of P. brassicas. were investigated: the carotenoids in the insect reflected those in the plant; male and female adults of P. brassicae seemed to possess similar amounts of carotenoids. In the plant there was a considerable variation in the carotenoids, both in quantity and in specificity. Age of the plant and season of growth were two factors, probably of several others, which were shown to influence the carotenoid content of the plant. The variation in the plant made it difficult to assess the significance of any variation in the earotenoids present in the insect. Feeding experiments showed that one larva during its life assimilated 77.79ug of b-carotene, which was 57.41% of the total b-carotene ingested. Of the total assimillted at least 66.10ug, that is 84.97%, was , Analysis of the frass indicated that greatest assimilation of p-carotene occurred at the end of the Lit larval stage. Labelling experiments seemed to show that carotenoids were sequestered from the haemolymph by the fat body four hours after ingestion. The carotenoid content of several other species of lepidoptera was determined. The results were often based on very different samples and therefore could not give reliable information about differences in amounts of carotenoid in the different species. However, they showed that earotenoids were present in all species studied. Lutein and b-carotene, two of the major plant carotenoids were found in all species in which individual carotenoids were determined and in all but examples either lutein or b-carotenewas the principal carotenoid in the insect. In species where males and females were available there was no apparent difference in the amount of carotenoids in the two sexes. Total carotenoids per -insect was shown to be positively correlated with the dry weight of the insect. Possible functions of earotenoids in insects are discussed, in particular as a source of vitamin A, in colouration and involvement in olfaction and toxicity.
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