2009 Volume 78 Issue 1 Pages 1_53-1_60
The gross and cell morphology and ultrastructure of larval labial glands of the sweet potato hornworm, Agrius convolvuli, were investigated by light, fluorescent and transmission electron microscopy. The labial gland is a narrow tubular epithelium that can be divided into three regions composed of hexagonal cells, each with a large branched nucleus. The ultrastructure of these cells was similar to that of silk gland cells in silkworms, characterized by well-developed rough endoplasmic reticulum and Golgi bodies. Agrius larvae spin small amounts of fibrous material immediately after hatching and at the wandering stage. Several bands (approx. 30, 67, 70, 116, 200kDa) were detected by SDS-PAGE from the labial glands throughout the fifth instar stage. Interestingly, most peptides disappeared at around the onset of the wandering stage, replaced by two proteins of approximately 180 and 220kDa. Two major polypeptides with similar molecular mass (180, 220kDa) were also detected in fibrous materials spun during the wandering stage. These results suggest that a switchover of protein synthesis occurs in the glands before metamorphosis.
