The evolution of knowledge in sericultural research as observed through a science mapping approach

General methodology and description of the software tools used

We followed four main steps to carry out the bibliometric analysis:

1. Datasets from different sources were extracted;

2. The data was cleaned up;

3. A particular analysis of the data was carried out, depending on the software tool used;

4. Lastly, the results were analyzed and discussed.

SciMAT²⁰ and the Bibliometrix²¹ R package (version 3.3.3) were used as tools for data analysis in this study. Both are used widely for bibliometric analysis studies. SciMAT is widely used for management and organization^22,23, virtual and remote labs²⁴, knowledge-based systems²⁵, marketing, and^26,27 in the field of social work. Bibliometrix is commonly used in businesses, healthcare, and public administration^28,29.

SciMAT is based on the science mapping analysis approach presented in 20, and allows us to carry out science mapping studies within a longitudinal framework^30,31. The SciMAT approach establishes four steps for analysis²⁰:

1. Detection of substructures, especially clusters of words, by means of co-word analysis over specific time periods

2. Generation of cluster diagrams based on results of the first step.

3. Generation and interpretation of evolution diagrams based on clusters and periods. This reveals the general evolution of the research field.

4. Analysis of the different time periods, clusters, and subject areas that have evolved using the various measures of density and centrality generated by the tool.

A strategic diagram represents the themes of the research field. Classification into four groups is achieved using the method proposed in 32 and 33 for equivalence index, normalized for a co-word network of keyword co-occurrence. The Simple Centres algorithm is based on 34 and the values of cluster centrality and density rank are based on 32. Based on centrality and density, the clusters can be classified into four groups:

1) motor

2) basic and transversal

3) emerging or declining

4) highly developed and isolated.

An analysis of the evolution of research themes was also undertaken to detect the general areas of evolution, based on a map.

Bibliometrix is an R package (version 1.8) that comes with options to import bibliographic data from SCOPUS databases. The user can perform a science mapping analysis and build data matrices for co-citation, coupling, scientific collaboration analysis, and co-word analysis.

Datasets and search methodology

This study made use of two of the most important databases for scientific literature, i.e. the core collections of Scopus and Web of Science (Web of Science).

The analysis was performed using SciMAT version 1.1.03, configured with the following parameters: Unit of analysis, Words (authorRole=true, sourceRole=true, addedRole=true); Kind of network, Co-occurrence; Normalization measure, Association strength; Cluster algorithm, Simple Centres (Max cluster size: 7, Min cluster size: 3); Evolution measure, Association strength; Overlapping measure, Association strength.

Some 1,883 records were obtained by Scopus and a further 312 by Web of Science, related to journal articles, notes, books, book chapters, reviews, and conferences. Following the deletion of duplicated records, the total of 2,195 was reduced to a final 1,930 records to be analyzed. On preliminary analysis, 91% of these were found to be for journals, with others totalling just 9%. We adopted a generalized definition of “Sericulture” which includes several different types of work on the silkworm (B. mori), mulberry (Morus spp), silk, and its industry. Some meaningless keywords that were too general, such as study or paper, were removed.

Using Bibliometrix as an R package does not require any special configuration. However, some steps based on R commands are needed:

1. Upload to R the download file in a character vector.

2. Convert the object to a data frame.

3. Apply the “biblioAnalysis” function that returns an object of class “bibliometrix”.

4. Apply the “biblioNetwork” function with the “collaboration” parameter for the “analysis” and the “countries” parameter for the “network” variable. This creates a collaboration network that is then plotted.

Data extraction

Figure 1 shows the amount of articles published on sericulture over time, from 1892 to 2016 (plus seven documents from 2017), for Scopus and Web of Science. The information covers a 124 year period, but 93% of records were from 1990 onwards. According to these results, it could be inferred that sericulture is an increasing area of research. Of the 1,930 records found, 531 were from the years 1892 to 2000, and 1,399 from the years 2001 to 2016.

Figure 1. Documents on sericulture published over time, as found in Scopus and Web of Science.

The most representative and influential journals that published on sericulture were mostly concentrated in Japan and India, except for Biomacromolecules, which is owned by the American Chemical Society.

The Journal of Sericultural Science of Japan and Japanese Journal of Human Geography are also listed, but to date these journals are not found in internationally indexed databases (Table 1).

Ten authors published 21.7% of the total research articles found, touching on various topics such as mulberry cropping, silkworm rearing, silk thread collection for the textile industry, and development of sericulture in different countries (Table 2). These ten authors have an affiliation from institutions located in India.

The country with the largest research output was India, with 1,242 records, much higher than the next two, Japan with 185 and China with 182. These three countries published 81.9% of the sericulture records found, and the ten most active countries produced 90% of the research (Figure 2).

Figure 2. The top 10 most active countries in sericulture research, between 1892 and 2016.

Thirty-one countries gave meaningful contributions to sericulture from all over the globe. By continent, Asia is represented by 14 countries, Europe by 9, America by 5, Africa by 2, and Oceania by one. There are isolated publications from 19 countries, including Brazil, Italy, Turkey, Iran, Spain, and Colombia (Figure 3). Other nations with a minimal number of records found in Web of Science include Croatia, Indonesia, Madagascar, Nepal, Pakistan, Paraguay, Romania and Russia.

Figure 3. Collaboration between countries, from 1892 to 2016.

Once the download references were uploaded in SciMat, a total of 2,518 keywords were extracted. Table 3 presents the top ten keywords identified. These keywords represent topics related to the concepts presented in Figure 4. This figure is based on the conceptual relationship between the keywords extracted, presented in clusters.

Figure 4. Relationship between the topics surrounding sericultural research mentioned in publications between 1892 and 2016.

Evolution and expansion of topics related to sericulture

Publications were divided into five consecutive time periods: 1892–2000; 2001–2005; 2006–2010; 2011–2013; 2014–2016. These time periods had 531, 461, 532, 225, and 181 publications, respectively (Figure 5) and we found 557, 844, 1,120, 853 and 852 keywords, respectively (Figure 6). It is important to note that the first time period covers 109 years, the largest amount of research was published in the 1990s (68%).

Figure 5. Documents published on sericulture from1892 to 2016 (1892–2000, 2001–2005, 2006–2010, 2011–2013 and 2014–2016).

Figure 6.

Keywords overlapping in the map of publications on sericulture: (a) 1892–2000, (b) 2001–2005, (c) 2006–2010, (d) 2011–2013 and (e) 2014–2016.

For the 1892–2000 time period 557 keywords were found. Between 2001–2005, 261 keywords did not reappear, 296 keywords migrated and 548 new keywords were mentioned. Between 2006–2010, 401 keywords did not reappear, 443 keywords migrated and 677 new keywords were mentioned. Then, between 2011–2013, 684 keywords did not reappear, 436 keywords migrated and 417 new keywords were mentioned. Finally, between 2014–2016, 499 keywords did not reappear, 354 keywords migrated and 498 new keywords were mentioned.

The number of keywords added in each of the four later time periods (64.9%, 60.5%, 48.8% and 58.5%, respectively) shows the vitality and expansion of the research field. Meanwhile, unchanged keywords between 38.9 and 53.1% (53.1%, 52.5%, 38.9% and 41.5%, respectively) point to the existence of certain base research topics (Figure 6).

The conceptual evolution of sericultural research (Figure 7) is represented by green, red and blue colours, denoting mulberry cultivation, worm breeding, and silk, respectively. There are no gaps in the evolution of most of the topics. Seven topics (Protein, Larva BM, Silk, Silkworm, Genetic, India) have been present in the field across the five time periods analysed and may thus be considered classic themes.

Figure 7. Conceptual evolution map separated into time periods.

Shows the most important elements and their development. (a) Per0:1892–2000, (b) Per1:2001–2005, (c) Per2:2006–2010, (d) Per3:2011–2013 and (e) Per4:2014–2016.

The topics (mulberry cultivation, worm breeding, and silk) exhibit a positive pattern of development because of the increasing number of subtopics within them. For instance, in the case of Fiber, it diversifies into Sericin, Genetic, and Stress in the second period (Per2). Similarly, Cocoon (Per2) comes from BM larvae (Per1) and diversifies into Preservation, India, Parasite, and Economic-Conditions. Some topics sustain the number of topics from previous periods and diversify into the next; this is the case for Microscopy (Per1) that comes from the initial period (Per0) of Cocoon and Protein and changes to Fiber and Stress in the following period (Per2) (Figure 7).

Research themes

To analyze the most prominent themes in the field of sericulture research for each time period, a strategic diagram is provided (Figure 8). In each diagram, sphere size is proportional to the number of records associated with each research theme.

Figure 8.

Research themes at different time periods according to the strategic diagrams (a) 1892–2000, (b) 2001–2005, (c) 2006–2010, (d) 2011–2013 and (e) 2014–2016.

Evolution of keywords related to sericulture over the last five years (2012–2016)

The evolution of keywords in the last 5 years is depicted in Figure 9 and Figure 10. The relationships between research themes are presented in Figure 11.

Figure 9. Documents published on sericulture in the last five years (2012–2016).

Figure 10.

Keywords overlapping map of sericulture publications in the last five years: (a) 2012, (b) 2013, (c) 2014, (d) 2015 and (e) 2016.

Figure 11. Relationship between the topics surrounding sericultural research in the last five years (2012 to 2016).

2012 begins with 405 keywords. In 2013, 224 keywords did not reappear, 181 keywords migrated and 278 new keywords were mentioned. In 2014, 279 keywords did not reappear, 180 keywords migrated and 299 new keywords were mentioned. In 2015, 301 keywords did not reappear, 178 keywords migrated and 238 new keywords were mentioned. Finally in 2016, 296 keywords did not reappear, 120 keywords migrated and 177 new keywords were mentioned. The addition of more than half the number of keywords in each period (60.5%, 62.4%, 57.2%, and 59.6%, respectively) and the fact that less than 45% of keywords remained the same (44.7%, 39.2%, 37.2%, and 28.8%, respectively) shows the vitality and expansion of this research field in the last five years (Figure 10).

The conceptual evolution of the field of sericulture research in the last five years (Figure 12), in which the theoretical evolution since 1892–2016 is represented by three colours exhibits cohesion; furthermore, there are no gaps in the evolution of the majority of thematic areas. Protein is the thematic area that is present across the five analyzed time periods, and is thus considered an established topic in sericultural research.

Figure 12. Conceptual evolution map for the last five years.

Shows the most important elements and their development. (a) Per0:2012, (b) Per1:2013, (c) Per2:2014, (d) Per3:2015 and (e) Per4:2016.

In the last five years, topics such as SILKWORM, Bombyx mori (Supplementary Figure S1a), MULBERRY (Supplementary Figure S1b) and SILK are mentioned. Even though in one or two time periods (in the case of Silkworm, for example) they are not found as nodes that are evidenced in the clusters, these topics have been permanent and predominant. In the case of SILK, it finishes up as a motor topic. With ECONOMIC-CONDITIONS, there are not enough registers in 2012 and 2013 for it to appear as a node, but it does appear in the Cocoon and Mulberry clusters (Supplementary Figure S2); over the last three years, there is no evidence of work on this topic. For DEVELOPING, in 2012, 2013, 2014 and 2016 there are not enough registers for it to appear as a node, but it appears in the Cocoon, Larva BM, Agriculture, and Silk clusters (Supplementary Figure S3).

COCOON (Supplementary Figure S4), INDIA (Supplementary Figure S5a) and BREEDS BM (Supplementary Figure S5b) are topics that appear in a diversity of clusters: for example COCOON appears in both Silkworm and Silk, BREEDS BM appears in Silkworm and Larva BM, and INDIA appears with Mulberry. With GENETIC, there is no evidence of nodes at any time period, but it is found within the Drug, Larva BM, Animals, Bombyx mori, and Physiology clusters (Supplementary Figure S6).

Research themes in the last five years

To analyze the most prominent themes in the field of sericulture in the last five years, a strategic diagram is provided (Figure 13).

Figure 13.

Sericulture research themes in the last five years according to the strategic diagrams (a) 2012, (b) 2013, (c) 2014, (d) 2015 and (e) 2016.

Distribution of records in Scopus and Web of Science

Three general time periods were identified for publications:

(1) Pre-1990s. Only 104 publications found, possibly because over that period publishing in annexed databases wasn’t common, and the priority was other kinds of documents such as technical reports from the centres dedicated to sericulture research and journals with no annexed databases;

(2) 1990s. Publications on sericulture begin to increase and specialized journals are created;

(3) Post-2000s. More than 76% of publications are from this time period, with strong growth in 2003, 2004, 2007, 2008 and 2009.

The publication dynamics in sericulture appear to be related to the history of fibres. Ever since the appearance of synthetic fibres (early XX century)¹⁶, the market has evolved thanks to the cost, ease of production, greater uniformity,¹⁷, such that they tended to push natural fibers out of the marker. However, in the last few years, natural fibres have been viewed as a sustainable option, 100% biodegradable, environmentally friendly, this has caused their use to diversify and increase¹⁸.

Core sericulture journals

The journals that have published the most on the topic of sericulture have a low impact factor that can be attributed to their specialization. The appearance and indexing of specialized journals such as Silk and India Journal of Sericulture in the 1990s lead to an increase in publication output. The total number of journals that have published sericulture related topics is 528. The top 10 journals account for 62.4% of the total contributions (1,206).

Most productive authors

Publications in the last 20 years have been led by authors from India. Notably, the Central Sericultural Research and Training Institute, founded in 1961 and directed by the Ministry of Textiles of the Government of India, is actively developing the silk industry in the country, and its researchers represent the most productive authors. From the total number of authors (3,058), ten have published 21.7% of the research output (420 documents) and 83.5% (2,555) have published one or more documents.

Most productive countries

The importance of India in the production of sericulture documents worldwide may lie in the investment the country makes in developing the silk industry, including silk centres, research institutes, specialized journals, and organized events. Publications with collaborations are evident; Japan has the most publications in collaboration with authors from other nations with 12 country links, followed by China with 10 and India with 6 links. This might suggest that collaborative work is missing between countries with an established research output and those looking at sericulture as an option for diversification and economic development, as is the case with Colombia and Brazil in South America¹⁹.

Evolution of topics related to sericulture

Generally, the keywords found were not linked just to one area of sericulture (mulberry cultivation, worm breeding, silk), showing that sericulture is multidisciplinary. It is worth mentioning that this research has shown that sericulture is dynamic and has faced new challenges created by environmental needs and scientific progress, as shown by keywords such as molecular, transgenic, genomic, sequence, and phylogenetic.