The Variation in Fat and Glycogen Content of the Bot Fly (Gastrophilus Intestinalis) Larva Tracheal Organ During Development

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Abstract
Numerous analyses on the chemical composition of various insects have shown that, as in mammals, fat and glycogen constitute the principal food reserves. Among holometabolic insects the accumulation of these two substances during the larval instars is, to a varying extent, utilized during the process of pupation. Most of the data on the chemical changes during metamorphosis are summarized by Needham (1942). However, as pointed out by Wigglesworth (1939), analyses of the body as a whole show only the gross alterations, and almost nothing is known concerning the composition of the separate organs. The only information available concerns the glycogen content of the isolated insect fat body; thus, Babers (1941) found that in the mature larva of Prodenia eridania (Lep.) the glycogen formed 23·3% of the fat body dry weight, while Yokoyama (1934) estimated the glycogen content of the silkworm fat body to vary from 2 to 17% of the dry weight according to age. No figures have been published for the fat content of the fat body, but histological evidence (Pardi, 1939; Wigglesworth, 1942) clearly demonstrates that fat is also present in high concentration.