The Origin and Dispersal of the Domesticated Chinese Oak Silkworm, Antheraea pernyi, in China: A Reconstruction Based on Ancient Texts

Sericulture is one of the great inventions of the ancient Chinese. Besides the mulberry silkworm (Bombyx mori), Chinese farmers developed rearing of the Chinese oak silkworm (Antheraea pernyi) about 400 years ago. In this paper, the historic records of the origins and dispersal of the domesticated Chinese oak silkworm in China are summarized. The first document with clearly recorded oak silkworm artificial rearing appeared in 1651, although Chinese oak silkworm was documented in about 270 AD. All of the evidence in the available historic records suggests that the domesticated Chinese oak silkworm originated in central and southern areas of Shandong Province in China around the 16th century, and then was introduced directly and indirectly by human commerce into the present habitations in China after the late 17th century. The results strongly support the hypothesis that only one geographically distinct event occurred in domestication of the modern Chinese oak silkworm.


Introduction
China is an ancient country with a very early agricultural history and the concomitant development of knowledge of entomology took place over a long period of time (Chou 1980;Zou 1981). Sericulture is one of the great inventions of the ancient Chinese. The mulberry silkworm, Bombyx mori Linaeus (Lepidoptera: Bombycidae) was successfully domesticated to produce the raw silk used for weaving by Chinese farmers about 5,200 years ago (Chou 1980;Goldsmith et al. 2004). Many people have heard of the mulberry silkworm, however few know much about the Chinese oak silkworm, Antheraea pernyi Guérin-Méneville (Lepidoptera: Saturniidae) that also originated in China.
The Chinese oak silkworm is one of the most well-known wild silkworms along with the Japanese oak silkworm, A. yamamai Guérin-Méneville, and the Indian oak silkworm, A. mylitta Hübner. The Chinese oak silkworm starts its life as a relatively larger egg that is about 0.01g in weight. Unlike the mulberry silkworm egg that can remain dormant, the Chinese oak silkworm egg soon hatches into the silkworm larva. The larva spins a cocoon in which it pupates and emerges from the cocoon as a moth. The moths mate and the female lays several hundred eggs. In southern China, including Henan and Guizhou Provinces, this cycle occurs once a year, but in northern China including the Liaoning, Jilin, Heilongjiang, and Neimenggu Provinces it can occur twice a year. Antheraea pernyi enters a pupal diapause in the winter. It feeds on the leaves of Quercus and produces a coarse silk. Today it is commercially cultivated mainly in China, India, and Korea for silk production, and is also used as a source of insect food (larva, pupa, moths) for human consumption and for cosmetics in China. About 70,000,000 kg of cocoons (pupae) are produced in China each year, accounting for 90% of world production. The production of cocoons in China's Liaoning Province accounts for 70% of world production. There are currently more than one hundred modern Chinese oak silkworm varieties in China which are divided into four lines based on the larval skin color: yellow, blue, white, and yellow-cyan. This species is also a well-known lepidopteran model system in studies of insect diapause, photoperiod effects, and neuroendocrine regulation (Maida 2000;Chang 2003;Wei 2008) due to its pupal-diapause and large size.
It is well accepted that Chinese oak silkworm was domesticated from its ancestor, a wild type of the Chinese oak silkworm in China (Zhang 1982;Hua 1987). Until now, several wild populations of Chinese oak silkworm have been found in different areas of southern China. A few of the characteristics of the domesticated Chinese oak silkworm have been altered from the wild state. First, the wild type has only a yellow-cyan larval skin color, whereas the domesticated counterpart has the four kinds of skin color mentioned above. Second, the wild type behaves as both univoltine and bivoltine in nature while semidomestic counterparts are exclusively either univoltine or bivoltine. Third, some individuals of wild populations can be kept in pupal-diapause for over two years until the moth emerges out from the cocoon (pupa), whereas no individuals from the domesticated populations can delay the diapause break. These changes presumably were caused by artificial breeding and selection.
About 400 years ago, Chinese farmers had begun to rear Chinese oak silkworm for producing the raw silk as floss. Here Journal of Insect Science | www.insectscience.org 3 successful domestication means that the rearing technology of Chinese oak silkworm, especially including stock selection and reservation, are essentially perfected and stable. Zhang (1982) and Hua (1987) examined the old texts for early records on the origin and radiation of domesticated Chinese oak silkworm in China. Zhang (1991) and Gu (1995) briefly mentioned history of Chinese oak silkworm production. To make it known to wider audience, in this paper we summarize the historic records on the origin and dispersal of domesticated Chinese oak silkworm in China. All these historic records suggest that only one geographically domestication event occurred in producing the modern Chinese oak silkworm. We believe that it is worth doing phylogenetic and geographic analyses to provide new insights into the origin and evolution of the domesticated silkworm species.
The earliest records of the Chinese oak silkworm The first document with clearly recorded oak silkworm is Guang Zhi, a book on ancient agriculture in China, written by Guo Yigong in about 270 AD. The description is as follows: "There has oak silkworm eating the leaves of oak tree, and the cocoon produced by it can be used as floss." The name of the oak silkworm comes from this book. However, this book only mentioned the collecting of the cocoons of Chinese oak silkworm from oak trees to make floss, rather than artificial rearing of oak silkworm.
Another document that records wild silkworms is Gu Jin Zhu, a book that explains many aspects of ancient and contemporary China; it was written by Cui Bao during the Western Jin Dynasty (265-340 AD). In this book he writes, "At the fourth year of Emperor Yongguang during the Han Dynasty (40 BC), there had wild silkworms emerging in Dongmou Mountain of Donglai County (now Mouping County in Shandong Peninsula). The wild silkworms become cocoons. The cocoons gave birth to moths that produced eggs on stone. About 10,000 Dan (135,000 kg) cocoons were collected to make use of raw silk as floss." This document is commonly cited and has gained widespread acceptance. In published papers the wild silkworm discussed in this book was considered to be the Chinese oak silkworm (Zhang 1982;Chen 1994;Gu 1995). It seems, therefore, that the collection of Chinese oak silkworm cocoons from the field to make floss dates back to at least 40 BC. However, no mention of artificial rearing of wild silkworms is made in this book. The silkworms are big, strong, and suitable to grow in the field, however sometimes they will be harmed by drought and by birds. The cocoon it produces is about 6 cm in length with a brown color unlike mulberry silkworm cocoon that is yellow or white. The cocoons like hen egg in size are hanging on the tree." This book, Shan Can Shuo, is the earliest known monograph on artificial rearing of Chinese oak silkworm to date (Yu 1987).
Another document that clearly recorded oak silkworm rearing is Meng Yin, a poem written in 1643-1661 by Zhang Gangsun. He noted, "It is very difficult to raise oak silkworms because it will take a long time to harvest. Silkworm eats the leaves of oak tree and drinks the early morning dew. To care silkworm, the people go to field very early and go home very late. Both ant and sparrow will harm the silkworm. People have to use slingshot to throw the soil-pill for driving away the sparrow every day, even in stormy It is difficult to verify when Chinese oak silkworm was successfully domesticated in Zhucheng of Shandong Province. After 1443, wild silkworms becoming cocoons had not been recorded as a good omen, probably showing that the oak silkworm management was realized sometime later. Zhang (1982) guessed that the rough date of the domesticated oak silkworm was after the midterm Ming Dynasty (around the 16th century).
During the period 1443 -and 1651 AD, there are three documents with records of the oak silkworm that should be considered. In the book Nan Yang Fu Zhi, the Records of Nanyang District in Henan Province, compiled from 1522-1566, it is mentioned that "There are two kinds of silks: mulberry silkworm silk and oak silkworm silk. The oak silkworm silk is produced by Nanshao, Zhenping, and etc., among them Nanshao produces the most oak silkworm silk." Today, farmers use oak trees to raise oak silkworms that live on the trees and produce a coarse silk unlike the soft mulberry silkworm silk. This is the earliest record in Henan Province on oak silkworm rearing. The book Gao Zong Shi Lu noted the letter to the Court written in 1744 by Shuo Se who is the leader of Henan Province. Shuo Se reported, "Recently many people from Shandong Province come here and carry the cocoons of oak silkworm to rear together with local farmers, and they have succeeded in silkworm stock and rearing method."

From Shandong to Liaoning
The book, Gao Zong Shi Lu, noted in a letter to the Court written in June 1762 by the provincial government, "There have lots of oak trees on the mountains in Jinzhou, Fuzhou, Xiongyue, and Gaiping areas, all of them belonging to Fengtian Province (now Liaoning Province). These oak trees can be used to raise oak silkworm for cocoon and then to weave the pongee. Now many refugees from Shandong Province come here to put up shanty for residing and raise oak silkworm for a living. They raise silkworms twice a year. After harvest, they produce pongee for a living." The book, Ta  Province, 1994).

Conclusions and Remarks
According to these historic records mentioned above, it is very clear that A. pernyi was first successfully domesticated in the central and southern areas of Shandong Province in China around the 16th century, and then introduced directly and indirectly by human commerce from central and southern areas of Shandong Province in China into the present habitations distributed over more than half of China after the late 17th century. Figure 1 shows the schematic diagram of origin and dispersal of the domesticated Chinese oak silkworm. The results support the hypothesis that only one geographically domestication event have occurred in the development of the modern Chinese oak silkworm. This is a testable hypothesis for which molecular fingerprinting techniques may be useful, as with the monarch butterfly (Zalucki and Clarke 2004). Preliminary data based on RAPD and ISSR markers carried out in our lab, and with collaborators, suggested the presence of high genetic variation (more than 90% of polymorphism bands) in A. pernyi (Liu et al. 2002Li et al. 2007). This indicates that the phylogenetic and geographic study of A. pernyi can be carried out to further test this hypothesis. Journal of Insect Science | www.insectscience.org 9 A better understanding of origin and evolution of domesticated species will help to improve domesticated organisms and open opportunities for new domestications. Genetic evidence has revealed many details, not available through historic records, about the origin and early history of domesticated species, including the domesticated silkworm (Pan et al. 2008) and many ungulate domesticated meat animals, e.g. sheep, cattle, pig, horse, goat, dog, donkey, water buffalo, and yaks (Guo et al. 2006 and the references). The domestication place and date of these domesticated species remain unclear; however, the domestication place and date of Chinese oak silkworm are clear. Therefore, we believe that phylogenetic and geographic studies of A. pernyi are worth doing to provide new insights into origin and evolution this domesticated species, and we welcome the collaborators to join us in this phylogenetic and geographic study of A. pernyi.
The Chinese literature from before 1900 mentioned in this paper is not listed in the references. English titles of papers and books that are only available in Chinese are approximate translations from the original Chinese title by the authors of the paper.