This website will provide up-to-date information on all silk insects around the wild silkworm Dear interested in wild silkworm and our members wild silkworm Society of Japan (JSWS).

　The following ten topics are from an article by Dr. Akai entitled 'Development and Contribution of the International Society for Wild Silkmoths', published in International Journal of Wild Silkmoth & Silk Vol. 7, 1-10 (2002) with additions of recent development as (4) and (6). Every topic is either achievement in basic research or achievement in technology development related to wild silkmoths, wild silkmoth cocoons, and wild silkmoth cocoon filaments and silk fabrics.

(1)　―Artificial diet―

　The artificial diets for Antheraea yamamai made complete larval rearing possible by 1964 (Fukuda & Higuchi), although problems of egg production and pupation remained. Composition of the diet was later improved and as were the rearing methods making the results much more satisfactory.

　More recently, a simple and convenient artificial diet for the rearing of the Eri silkmoth was developed (Shimizu & Akai, 1992), as was, a paste-like diet using fresh leaves which greatly lowered costs (Shimizu et al.). These diets also serve to prevent insect diseases such as virus and bacteria, if used during the younger larval stages, and result in increasing the yield to more than twice the usual.

Artificial diet for Antheraea yamamai

Paste-like diet made from fresh leaves

(2)　―Hormonal control of embryonic diapause of wild silkmoths

　Practical utilization of artificial hatching by HCl treatment for diapause Bombyx eggs was first developed by Koike (1914), and perfected later (Araki et al., 1917). Their methods, however, were not effecting for diapausing eggs of other silkmoths, and there has been no further progress to date.

　Insect endocrinologists recently demonstrated that an anti-juvenile hormone inhibits ecdysone and JH in haemolymph. It was also demonstrated that larval molting and silk production of B. mori are controlled by anti-juvenile hormone treatments (Akai et al.). Suzuki et al. (1990) found that the AJH breaks down the egg diapause of A. yamamai , and the hatching ratio is more than 90%. These findings are of great value in botyh the developmental and commercial fields of wild silkmoth.

Different cocoon size produced by application of bioactive substances at different developmental time

Artificial hatching of diapause eggs of Antheraea yamamai using imidazole compounds

(3)　―Ultrastructural characteristics of wild silkmoth cocoon filaments―

　Generally, structural characteristics and size of the cocoon filament are very important in post-cocoon technology, because these characteristics have strong influence on the final nature of the silk fabric.

　Since our report in 1989 on fine-vacuolar structures of the cocoon filament and liquid silk in the silk gland of A. yamamai (Akai et al., 1989), the structural characteristics of the cocoon filament have received attention both from the aspect of research and post-cocoon technology. We compared various cross sections of cocoon filaments from the silk-spinning insects of 5 families and 15 species. The results clearly showed that all of the filaments from Saturniidae insects were porous, and the filaments of all others were compact (non-porous).

　From the viewpoint of commercial use, it can easily be understood that the porous filaments is preferable for textiles which have a soft feeling as it retain a moderate humidity and temperature in the textile. These findings are also very important for the development of silk textiles.

Cross section of cocoon filaments

Ultrastructural characteristics of wild silkmoth cocoon filaments

(4)　―Silk gland fibroinase―

　In 1993, Sumida et al. reported that fibroinase, enzyme that hydrolyzes liquid fibroin, was recovered from silk glands at day one pupa and also from silk glands at the fourth molt period of the fourth instar larva of the domesticated silkworm, Bombyx mori. Later, fibroinase was shown to hydrolyze sericin as well. Sumida et al. demonstrated that silk glands of Eri silkworm Samia cynthia ricini contains fibroinase and that it can be purified. Fibroinase of B. mori and S. cynthia ricini is cathepsin L-like cysteine proteinase and functions optimally at pH 4.0.

　One of the features of fibroinase of Eri silkworm is that at end of spinning, absolute activity reaches very high, as high as 38 times the highest activity of B. mori fibroinase in silk glands. Fibroinase in silk glands of Eri silkworm at end of spinning is a good enzyme source for enzymatic degumming of cocoon filaments and silk fabrics.

　Akai et al. demonstrated that numerous small pores in cocoon filaments and liquid fibroin in luminal contents of posterior silk glands of Antheraea yamamai described in (3) are remains of lysosomes secreted from posterior silk gland cells. Fibroinase is normally contained in these lysosomes. At each molt period, B. mori and S. cynthia ricini secrete fibroinase into luminal contents of silk glands. Molecular mechanism of fibroinase secretion is not clearly understood.

　As for cocoon digestion, cocoonase is famous, which is synthesized and secreted from galleae located at both sides of adult moth mouth. Cocoonase is serine proteinase and functions at slightly alkaline pH such as pH 8.0. Cocoonase digests sericin only and does not digest fibroin.

　For enzymatic degumming, alkalase is now routinely used, which removes sericin from cocoon filaments and silk fabrics at alkaline pH. Its use may be derived from knowledge of cocoonase. Fibroinase hydrolyzes sericin as well as fibroin. It could be utilized as new degumming enzyme. Degumming by fibroinase may add slightly different feature and texture of cocoon filaments and silk fabrics.

Fibroinase absolute activity of Eri silkworm silk glands

(5)　―Gene technology of wild silkmoths―

　Several interesting reports have been made on the gene technology of wild silkmoth. In Antheraea pernyi , the structure of the polyhedrin gene of nuclear polyhedrosis virus was analyzed, with the result that an expression vector which can produce a foreign protein. Also, an insect baculovirus vector expression system using Autographa californica nuclear polyhedrosis virus and Bombyx mori nuclear polyhedrosis virus was constructed to express foreign gene (Wang, 2001). This research field is rapidly expanding in both basic and applied research, not only for silkmoths but the biological areas of all insects.

Interferon production

(6)　―Cocoon production efficiency of transgenic, domesticated silkworms with Antheraea yamamai fibroin gene

　Our previous study demonstrated the introduction of a fibroin gene of normal domesticated silkworm into Nd-s domesticated silkworm mutant (that had an abnormally small posterior silk gland (PSG) and secreted only sericin) to produce transgenic domesticated silkworm and observed its PSG and lumen (Akai et al., 2006). As a result of fibroin gene introduction into the Nd-s mutant, a clear functional recovery of fibroin secretion and fibroin synthesis in the PSG cells were observed.

　In the present study, PiggyBac transposon was used to introduce a fibrion gene (Ayfib) of Antheraea yamamai into a normal domesticated silkworm to produce transgenic (TG) silkworms. The TG silkworms were observed for posterior silk gland cell activity and fibroin morphology. The TG silkworms did not have uniform cocoon filament and their fibroin contents were only about 11% of that of a control. The TG silkworm had poorly developed PSG and unclear cytoplasmic infolding in the PSG cells. Moreover, ER, Golgi complex, and fibroin globules were poorly developed and few in the TG silkworms. Thus, the transgenic silkworms produced by this method were clearly shown to have low protein synthesis activities.

　Based on the present and previous results, some clue to discern control mechanisms of fibroin gene expression in silk-spinning insect silk glands will be obtained. Wild silkmoth silk glands and wild silkmoth fibroin gene and sericin gene provide us indispensable biological and molecular tools to study biological features of wild silkmoths and offer opportunity for new technology development.

Silk glands of transgenic silkworms

Cross section of central part of posterior silk gland

(7)　―Silk powder from wild silkmoths―

　Fibroin of A. pernyi was hydrolyzed under phosphoric acid solution, and water-soluble peptide powder was produced at lower than usual cost (Wang et al., 2001). About the same time, Eri silk powder was also successful by a similar method. Various types of wild silk powder are now being researched and developed by several physical methods without using chemical treatment, because of increasing demand for wild silk powder from various industries.

(8)　―Coloring materials from wild silkmoth cocoons and utilization of Cricula trifenestrata―

　Some wild silkmoths produce variously colored cocoons and filaments, such as A. yamamai and Rhodinia fugax which produce green, ecorace of Samia cynthia with reddish brown, and Muga silk which is called "golden raw silk", and the golden Cricula cocoon. These naturally colored materials from the cocoons are now being biochemically analyzed (Yamada & Kato).

　Utilization of the natural color cocoon and filament produces unique and highly valued silk textiles, such as Tensan(A. yamamai ) silk and Muga (A. assama ) silk. Cricula golden cocoon is perhaps the most unique case. In Yogyakarta, Cricula is the only pest that is harmful in orchards and roadside trees. There had previously been no idea of utilizing these moths, but now the area is growing a nursery silk industry of Cricula.

Cocooning of Cricula trifenestrata larvae and earrings made by the cocoons

Muga raw silk from Assam, India

(9)　―Huge cocoon nest and social silkmoth, Anaphe―

　Mature larvae of Anaphe collaborate to make a huge silk nest which is composed of a common silk shell and numerous individual cocoons (Akai et al., 1999). A special stimulating vapor released from the nest causes the skin to itch when touched by the human hand. By degumming, however, we no longer feel this sensation which means that the stimulating chemical is contained in the sericin of the cocoon filaments. Each silk filament is extremely flat in cross section and compact, without any fine porous structure. A new method of degummming for Anaphe cocoon filament has been developed.

　Recently, thiaminase was first detected in Anaphe larvae, pupae and moths, in a fairly large quantity. To date, this is the only such case among all insect species.

Huge cocoon nests of Anaphe including numerous matured larvae inside

(10)　―Functions of wild silks―

　The role of the cocoon shell and cocoon nest must be to protect the moths from a severe environment, for instance, high and low temperatures and prevailing humidities, as well as various natural enemies. Therefore, the cocoons themselves must have protective functions against the environment.

　From UV reducing experiments, it was concluded that wild silk materials are vastly superior in UV absorption and ability to UV transmission and also superior in reducing UV (Akai et al., 1999). Other simple tests examined the anti-fungal function of certain silk materials using Japanese mochi (pure rice cake with no other ingredients). These tests indicated that wild silk materials apparently do have property inhibiting fungal proliferation.

　Nutritional studies of wild silk powders are now suggesing new functions for these wild silk materials: the control of cholesterol in blood, resistance to large intestinal cancer, and an anti-oxidation function.

Ability of UV transmission

Anti-fungal activity of dry powder of silk from different insect species

　The above topics are only a few of the many interesting findings recorded during the long period since the Society was established in 1988. We have many basic and applied problems of wild silkmoths and silks to resolve or make progress on in the near future. Wild silkmoth research is thus not yet very advanced, and has many unresolved aspects. However, we strongly feel that resolution of the problems of wild silkmoths and silks can and will undoubtedly be developed by our society.