Silk used normally is produced by tetramoulter silkworms which is coarse and difficult to transform into ultrafine fibers. In recent years, ultrafine fiber has been widely used in many fields because of its high detergency, heat preservation, softness and lightness. Ultrafine fiber can be converted into ultrafine fabric, where, the fabric surface is extremely smooth, and it exhibits minimal air resistance; its optical properties (e.g., the refractive index, transmittance and reflectance) differ significantly than traditional fabric. Indeed, the lightweight fabrics and clean cloths of ultrafine fibers are popular in Japan and Europe. In sericulture, thin silk fibers are typically obtained by breeding trimoulter strains or inducing normal tetra-moulters into trimoulters which suggests that further reducing the number of moults could produce thinner silk. To date, numerous studies have focused on trimoulters induced by hormone-like chemicals. For example, Asano and others, first introduced and successfully applied Anti-Juvenile Hormones (AJHs) that induce tetramoulter silkworms into trimoulters, whereas, Zhuang and his group, induced two Chinese tetramoulter silkworm species into trimoulters using the imidazole compound YA_(20).
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