Distribution of nutrient reserves during spinning in tissues of the larva of the fly, Rhynchosciara americana

The amount of protein, carbohydrate, lipids, and free amino acids were examined in the spinning stage in the fat body, haemolymph, skeletal muscle, and gut of Rhynchosciara americana. Protein and lipids increase in the fat body soon after the animal stopped feeding, probably at the expense of the digestion of the gut contents and of the reserves of the gut wall. Afterwards there is a fall in protein and lipids in the fat body. Haemolymph protein rises a little at the beginning of spinning and then decreases steadily during cocoon production. Carbohydrate and free amino acids decrease from the beginning of spinning in all tissues studied. Quantitatively, the most important decrease of carbohydrate during spinning occurs in the fat body whereas that of free amino acids occurs in the haemolymph. Lipid increases during spinning in the skeletal muscle, probably due to enlargement of the lateral fat body which occurs as a contaminant in the skeletal muscle preparation. The Malpighian tubules contain a large amount of calcium carbonate, which is eliminated during spinning. A correlation of our chemical data with histochemical data recently published is presented and the physiological implications of our findings are discussed in comparison to other insects.