Fine morphology and amino acid analysis of the egg capsule of the stick insect, Clonopsis Gallica (Charp.) (Cheleutoptera: Bacillinae)

Abstract

The scanning electron microscope morphology and the amino acid composition of the egg capsule of the stick insect Clonopsis gallica have been studied. The egg capsule shows an irregular but characteristic pattern of rounded tubercules, which at higher magnifications reveal a still more detailed sculpturing. The micropylar plate shows specific structural characters, including a shallow square micropylar cup without micropylar orifices; ovariolar eggs, however, show a number (from 3 to 5) of wide, open micropyles. The opeculum does not possess the capitulum nor the pseudocapitulum, but among the prominent tubercules of the central area some aeropyles are present. The thick 3-layered chorion has a uniformly smooth internal surface; the spongy submicropylar plate possesses a tubule connecting the chorion to the vitelline membrane. The amino acid composition has revealed that glycine is the most common residue (33%), followed by serine and alanine (about 10% each), with traces of cystine and methionine. SEM features specifically identify the egg of C. gallica but also reveal some genuine similarities with the egg of B. rossius. The meaning of the existence of the micropylar orifices during egg development has been discussed. The amino acid composition is a new datum for the Cheleutoptera and it has been compared with that of insects having an orthopteroid structure. In particular, the high glycine content in C. gallica egg shell suggests a certain resemblance with the species of 5 families of Tettigonioidea, whilst there are definite differences with species of Gryllidae and Acrididae. Thus, the egg morphology and amino acid composition data can be utilized as aids in understanding the phylogeny and egg physiology in several insect orders.