Studies on the Cocoon of the Oriental Moth, Monema (Cnidocampa) flavescens, (Lepidoptera: Limacodidae). III. Structure and Composition of the Cocoon in Relation to Hardness

Abstract

The Oriental moth, Monema (Cnidocampa) flavescens Walker, constructs a very hard cocoon shaped as a sparrow-egg. So far as it is known this cocoon is the hardest among the cocoons constructed by Japanese insect species. The cocoon shell is composed of 4 or 5 layers with different characteristics and has a spheroid shape. The percentage of cocoon shell accounts for more than 20% of the cocoon. These characteristics are considered to be the physical factors responsible for the resistance of the cocoon to pressure. The cocoon shell contains about 34% of protein from two different origins: l) silk protein produced in the silk glands, and 2) protein presumably secreted by the salivary glands. The latter protein is plastered into the silk net and its color changes from pale to dark brown while sclerotizing at the same time during the course of the cocoon construction. The cocoon shell protein contains a high concentration of β-aIanine of the same nature as that of the sclerotized protein in the insect cuticle. The cocoon shell contains about 35% of ash. Calcium predominates among the cations, and is mainly localized in white patches on the cocoon as crystals of Ca-oxalate which are produced in the Malpighian tubes and excreted from the anus. It has long been considered that the hardness of the cocoon can be ascribed to a calcification process. The results obtained presently do not support this assumption. Based on chemical data it appears that the hardness of the cocoon is not due to a process of calcification, but to the presence of a fine silk net filled compactly with the sclerotized protein. © 1984, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.