Structure and properties of silk from the African wild silkmoth Gonometa postica reared indoors.

African wild silkmoth, Gonometa postica Walker (Lepidoptera: Lasiocampidae), were reared indoors in order to examine the influence of rearing conditions on the structure and properties of silk cocoon shells and degummed fibers by using a scanning electron microscope, an Instron tensile tester, and a thermogravimetric analyzer. The cocoons reared indoors showed inferior quality in weight, length, width, and cocoon shell ratio compared to cocoons reared outdoors. There were no differences in cocoon shell and fiber surfaces and cross sectional structures. Cocoon shells were covered with calcium oxalate crystals with few visible fibers on their surface. Degummed fibers were smooth with minimum unfractured surfaces and globular to triangular cross sections. Indoor-reared cocoon shells had a significantly higher breaking strain, while the breaking stress was higher for cocoons reared outdoors. Fibers from indoor cocoons had a significantly higher breaking stress while outdoor fibers had higher breaking strain. Thermogravimetric analysis curves showed two main thermal reactions revealing the dehydration of water molecules and ir-reversible decomposition of the crystallites in both cocoons and fibers reared indoors and outdoors. Cocoon shells underwent additional peaks of decomposition with increased temperature. The total weight loss was higher for cocoon shells and degummed fibers from indoors. Rearing conditions (temperature and relative humidity), feeding method used, changes in total life span, days to molting, and spinning might have influenced the variation in the properties observed.The ecological and commercial significances of indoor rearing of G. posticaare discussed.

Study on the microstructure of African wild silk cocoon shells and fibers.

Silk fibers and cocoon shells from four African wild silkmoths Gonometa postica, Anaphe panda, Argema mimosae and Epiphora bauhiniae-were studied to gain insight into the structure-property-function relations and potential commercial application. The surface and cross-section of cocoon shells and fibers revealed the presence of prominent structural variations. Cocoon shells were multilayered and porous structures constructed from highly cross-linked fibers that are densely packed within the sericin/gum. Fibers had fibrillar sub-structures running along the fiber axis and with greater number and size of voids. The ecological significance and implication of these structures for further application are discussed.