Studies on the structure of the integument of the silkworm, with special reference to its cuticular lipids

Abstract

Hydrocarbon contents were compared about the lipids of exuviae obtained from larval, pupal, and imaginal molting, and superficial lipids of cuticle of the living 5th instar larvae and pupae. Consideration was also given about the role of the hydrocarbons in molting procedures. In order to study the influence of the foods on the exuvial lipids composition, comparison was made about exuviae of the 5th instar and pupae reared on mulberry leaves and those reared on prepared foods. 1) n-C27 exists in the largest amount in all of the exuviae samples and superficial lipid samples of cuticle of living larvae. The exuviae of the 4th instar contains more than 10% each of n-C25, n-C27, n-C29 and n-C31, and the exuviae of the 5th instar and the superficial lipids of the 5th instar n-C25, n-C27 and n-C29. The exuviae of pupae and the superficial lipids of pupae contain more than 10% of n-C27 only hydrocarbon. 2) n-alkanes is contained to the amount of 95.2% of the hydrocarbons content in the exuviae of the 4th instar. But the hydrocarbon content decreases with the metamorphosis pupation and imagination…to 35.4% in the exuviae of the pupae. The iso-alkane content on the hand, increases with metamorphosis. 3) The total odd chain content is 90.3% in the exuviae of the 4th instar, but it decreases with metamorphosis. It is only 48.7% in the exuviae of the pupae. The total even chain content, on the other hand, increases with metamorphosis. 4) The exuvial lipids content which increases greatly just before pupal molting contains much iso-alkanes. This seems to ease the pupal molting in the cocoon. 5) Compared with those reared with mulberry leaves, in case of those reared with prepared foods, the lipid hydrocarbons composition in the stage of pupal molting is more similar to that of larval molting. © 1974, The Japanese Society of Sericultural Science. All rights reserved.