International Journal of Biological Macromolecules 50 (2012) 63–68 Contents lists available at SciVerse ScienceDirect International Journal of Biological Macromolecules jo u r n al hom epa ge: ww w.elsevier.com/locate/ijbiomac Study on the microstructure of African wild silk cocoon shells and fibers Addis Teshome a,c,∗ , Fritz Vollrath b , Suresh K. Raina a , J.M. Kabaru c , J. Onyari c a icipe-African Insect Science for Food and Health, P.O. Box 30772-00100, Nairobi, Kenya b University of Oxford, Department of Zoology, Silk Research Group, South Parks Road, Oxford OX1 3PS, UK c University of Nairobi, School of Biological and Physical Sciences, P.O. Box 30197-00100, Nairobi, Kenya a r t i c l e i n f o Article history: Received 9 August 2011 Received in revised form 26 September 2011 Accepted 27 September 2011 Available online 5 October 2011 Keywords: SEM Voids Wild silkmoth a b s t r a c t 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 rela- tions 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. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. 1. Introduction Silk, from both domesticated and wild silkworms and spiders, represents a unique and important class of polymeric composite materials in nature providing a wide range of evolutionary and ecological functions with optimum microstructures and proper- ties [1,2]. Larvae of silkmoths spin silk threads and form cocoon shells to enwrap themselves completely prior to metamorphosis. These cocoon shells are non-woven structures majorly composed of two proteins, fibroin and sericin. They exhibit extensive varia- tion in structure, property and composition which imposes direct influence on their adaptive function. The functional significance of these proteinaceous structures includes crypsis, provision of barricade from predators, pathogens and parasitoids and assisting the pupae to complete their metamorphosis by improving ther- mal and/or moisture conditions [3]. The multitude of variations in diet, breed and climate resulted in considerable diversity in the type and properties of the cocoons and fibers produced by silk pro- ducing insects of different origins and within the same type. Thus, species-specific fiber mechanical, chemical and physical properties reflect the ecology and behaviour of cocoon-spinning insects [4,5] and can significantly influence the quality, quantity and efficiency of the reeling process in commercial varieties [6]. ∗ Corresponding author at: icipe-African Insect Science for Food and Health, P.O. Box 30772-00100, Nairobi, Kenya. Tel.: +254 20 8632054; fax: +254 20 8632001/2; mobile: +254 719 698782. E-mail addresses: additi09@gmail.com, akebede@icipe.org (A. Teshome). Studies have shown the existence of macro- and microscopic level structure and property variations among cocoon shells and fibers from mulberry and wild silkworms. Narumi et al. [7] revealed the presence of a large number of voids in the cross-sections of wild silk fibers in contrast to mulberry silk. The silk fibers from the wild silkmoths have many longitudinal striations on their sur- face and are porous which make them lighter than mulberry silk [8]. Wild silk fibers also consist of flattened, ribbon-like filaments of much greater diameter than mulberry silk [9]. Although the potential of African wild silkmoths for production of large cocoons with economic importance has been documented, the microscopic structure and properties of these fibers and cocoon shells have not been studied in detail. Comprehensive studies of such struc- tures will lead to better understanding of the cocoon spinning behaviour of the silkworms and how silk fibers are arranged in the cocoon shells to suit their designed purposes. This informa- tion would be of immense value in the prudent evaluation of the potential of silks for commercial application and further investigate the structure–property–function relations of silk fibers and cocoon shells. In this study, we investigate the surface and cross-sectional structures of silk fibers and cocoon shells produced by four species of wild silkmoths using scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. 2. Materials and methods 2.1. SEM study on surface and cross-sections of cocoon shells Cocoon shells of four wild silkmoth species (Anaphe panda Bios- duval, Argema mimosae Biosduval, Epiphora bauhiniae Guer and 0141-8130/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.ijbiomac.2011.09.025