Studies on the digestion of wool by insects. IV. Absorption and elimination of metals by lepidopterous larvae, with special reference to the clothes moth, tineola bissellielal (humm.).

The fate was investigated of 30 metallic and five non-metallic elements following ingestion by Tineola larvae. When incorporated in woollen fabric or in a yeast-casein medium, 19 elements that form insoluble sulphides produced characteristically coloured sulphides in the food undergoing digestion in the midgut. The production of the sulphides is brought about by the alkaline, highly reducing, midgut secretions,. which cause the production of sulphydryl groups by the reduction of the Clisulphide bonds of the cystine present in the wool. When metal is present in the diet less cystine is excreted than on a normal diet. Othe.r sulphur-containing compounds ( methionine, glutathione) also permit the formation of sulphides. Much of the sulphide formed passes down the digestive tract and is excreted. However, a certain amount forms highly dispersed colloidal solutions with the amino acids or polypeptides liberated by digestion of the food or present in the digestive secretions. These colloidal sulphides are taken up by the midgut epithelium, and granules of sulphides accumulate in the cavities of the goblet cells of the anterior and posterior regions of the midgut. Sulphides of fewer metals accumulate in the goblet cells of the middle region of the midgut. All goblet cell accumulations are eHminated during moulting, when the entire midgut epithelium is cast off and regenerated. The goblet cells of other lepidopterous larvae were also shown to accumulate some metals, although not as sulphides.