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. 2014 Mar 7:14:36.
doi: 10.1093/jis/14.1.36.

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

Addis Teshome  1 , S K Raina  2 , Fritz Vollrath  3
Affiliations

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

Addis Teshome et al. J Insect Sci. .

Abstract

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.

Keywords: cocoon quality; scanning election microscopy; stress-strain curve; thermal property.

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Figures

Figure 1.
Figure 1.
1A) Indoor fiber surface, (1B) outdoor fiber surface, (1C) outdoor fiber cross section, (1D) indoor fiber cross section, (1E) indoor cocoon shell surface, (6F) outdoor cocoon shell surface, (1G) outdoor crystals, (1H) indoor crystals, (1I) outdoor cocoon shell cross section, (1J) indoor cocoon shell cross section. High quality figures are available online.
Figure 2.
Figure 2.
FTIR spectra of pure calcium oxalate (blue), outdoor-reared (red) and indoor-reared G. postica (green) outer cocoon shell surface. High quality figures are available online.
Figure 3.
Figure 3.
Stress-strain curves of Gonometa postica (3A) indoor cocoon shells, (3B) outdoor cocoon shells, and (3C) degummed fibers. High quality figures are available online.
Figure 4.
Figure 4.
Thermogravimetric analysis curves for indoor- and outdoor-reared Gonometa postica silk cocoon shells and degummed fibers. High quality figures are available online.
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