Abstract

SummaryG. Labour: Ultrastructural study on the evolution of the Colorado Beetle fat cells throughout the larval and nymphal development.The ultrastructural study of the Colorado Beetle fat cells shows three successive periods throughout the larval and nymphal development.During the first phase (until the termination of the third larval instar), the cells contain very numerous ribosomes and mitochondria, which is indicative of an active metabolism. The cells accumulate lipid and glycogen inclusions. According to the respective extension of vacuoles and storage deposits, internal and external fat cells layers can be distinguished.The second phase starts with intensive cellular proliferation (beginning of the fourth larval instar). The cells contain some large vacuoles, that seems to develop at the expense of the reticulum, few organelles and prominent storage materials. Then, cytolysomes make their appearance; their contents are progressively lysed, which result in myelin bodies and urate crystals. Internal fat cells can be differenciated into dorsolateral cells with numerous cytolysomes, and periintestinal cells.During the third phase, many cells are lysed: proteins disappear, membranes are broken down, and cellular rubbishes are released into the hemolymph. Other cells survive in imago. Depending on the fat body lobe studied, this process occurs sooner or later, throughout the pre-imaginal instars, and constitutes the turnover of insect components required for metamorphosis.

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