Year-Round Muga Silkworm Rearing for High-Quality Silk Production

Muga silk – often called the golden silk of India – is one of the rarest and most prized textiles in the world. It is produced by Antheraea assamensis, a semi-domesticated silkworm endemic to Assam and parts of Northeast India. Unlike mulberry silk that is reared indoors on controlled farms, Muga rearing happens largely outdoors on living trees, making it deeply tied to the landscape and seasons of its home region. For farmers and students of sericulture alike, understanding the complete rearing cycle – from plantation preparation to cocoon harvest – is essential for consistent, high-quality silk production throughout the year.

The multivoltine nature of Muga silkworms 🔗

A key advantage of Muga culture is the silkworm’s multivoltine nature, meaning it can produce multiple generations in a year. According to the Central Silk Board of India, farmers raise 5 to 6 crops annually. These include two main commercial crops – Jethua (May-June) and Katia (October-November) – two pre-seed crops (Jarua in December-January and Aherua in June-July) and two seed crops (Chotua in February-March and Bhodia in July-August). The commercial crops are conducted when climatic conditions are most favorable, while pre-seed and seed crops often face greater risks from adverse weather, disease, and pest pressure.

The Jethua spring crop (April-May) is particularly prized, as it yields the produce most suitable for commercial silk. Indian Culture portal notes that while cocoons are generated multiple times a year, the Jethua season is the primary commercial crop season for Muga farmers.

Host plants: Som and Soalu 🔗

Muga silkworms feed primarily on two host plants: Som (Persea bombycina) and Soalu (Litsea polyantha). The choice between them often depends on geography – Som is more common in upper Assam and is associated with reeling-quality cocoons, while Soalu is prevalent in lower Assam and is more suited for seed cocoon production. Secondary food plants such as Mezankari (Litsaea citrata), Dighalati (Litsaea salicifolia), and Bogori (Ziziphus jujube) can supplement feeding when primary plants are scarce.

Research published in the Annals of Forest Research confirms that Som consistently delivers superior performance for larval weight, cocoon weight, shell weight, and the effective rate of rearing (ERR). Combined Som-Soalu sequences during early and late instars are also shown to produce strong results, giving farmers some flexibility in plantation management.

Preparing the plantation 🔗

Site selection and plantation management are non-negotiable first steps. The Directorate of Sericulture, Assam recommends selecting well-drained, elevated land in a shady location for nursery preparation. The soil should be dug or ploughed to a depth of 30 cm and enriched with farmyard manure (FYM) before transplanting seedlings. For rearing preparation specifically, plants are pruned to 6 feet height – 4 months prior to rearing for early-stage larvae and 5 months prior for late-stage larvae – and fertilized with N:P:K at the ratio of 44:62:17 g per plant after pruning.

Before each rearing cycle, the plot must be disinfected. A bleaching powder and slaked lime mixture (1:9) is dusted at 200 g/m² at least twice at 3-4 day intervals, starting 8-10 days before brushing (placing newly hatched worms on trees). Four days before brushing, 0.01% sodium hypochlorite solution is sprayed on the foliage of the chawki rearing plot, twice at 24-hour intervals, to reduce pathogen load on leaves.

Egg handling and early-stage rearing 🔗

Only microscopically examined, disease-free eggs (disease-free layings or DFLs) should be selected for rearing. Eggs are incubated at 26 ± 1°C and 85 ± 5% relative humidity. Only worms that are 1-3 days old after hatching are considered suitable for brushing onto plants – older or irregular hatchlings are excluded to maintain uniformity and reduce disease risk.

The standard practice is to brush 2-3 DFLs per plant, with the carrying capacity of the individual plant assessed visually. Worms should ideally reach the 4th instar on the same tree without needing to be transferred. During brushing, timing also matters: the Central Silk Board advises brushing newly hatched worms between 5 and 7 AM – on the shaded side of the plant during summer, and toward the sun during winter. Nylon nets are used over the chawki (early instar) plants to protect young larvae from pests and predators while maintaining adequate ventilation inside the canopy.

Indoor chawki rearing: managing monsoon risks 🔗

The early larval stages (instars I and II) are the most vulnerable point in the entire rearing cycle. Studies have shown that in an average season, over 50% larval loss can occur, with the majority of this loss concentrated in the 2nd and 3rd instars due to abiotic stress – including heavy rainfall, hailstorms, and fluctuating humidity during the monsoon period.

Indoor chawki rearing was developed specifically to address this problem. In this method, early-instar worms (up to the 2nd or 3rd instar) are reared indoors on cut Som or Soalu twigs placed in wet sand or water-filled bottles, then transferred to outdoor trees once they are stronger. Research consistently shows that this hybrid approach – indoor chawki rearing followed by outdoor late-age rearing – produces significantly higher survival rates, cocoon weight, and effective rate of rearing compared to either fully indoor or fully outdoor methods. The comparative rearing study published by Agricultural Science Group found that rearing up to the 2nd instar indoors before moving worms outside yielded better cocoon and shell weights across all seasons tested.

Chawki rearing has now been formally introduced into Muga culture as a standard technique, especially during adverse seasons. The concept is considered effective for improving overall production outcomes, particularly for pre-seed and seed crops that often coincide with difficult weather windows.

Late-age rearing and predator management 🔗

Once larvae reach the 4th and 5th instars (late-age), they are reared entirely outdoors on standing Som or Soalu trees. At this stage, worms eat heavily and grow rapidly. Managing the rearing plot becomes more about protection and monitoring than controlling the environment.

The main threats during late-age rearing are predators and parasitoids. The Farmer’s Guide to Muga Silkworm Rearing identifies the Uzi fly as a major pest, particularly in winter months (November to February), causing heavy losses during cocoon harvest by parasitizing 4th and 5th instar larvae. Wasps (Vespa orientalis) are active from April to September and target late instars directly. Ants and the parasitoid Apanteles glomeratus also pose significant risks during summer crops. Chemical control is strongly discouraged because pesticides harm the silkworms themselves.

Practical measures against predators include:

• Wrapping tree trunks with oil-coated polythene sheets to block predators from climbing up and to prevent worms from crawling down.
• Minimizing unnecessary handling of worms to avoid stress and injury.
• Using disinfected chaloni (bamboo sieves) when transferring worms to fresh trees, transferring only healthy and uniformly developed larvae.
• Spraying 0.01% sodium hypochlorite solution twice in each instar to reduce bacterial and viral disease outbreaks.

Overcrowding on both the chaloni and the new plant must be avoided, as dense populations accelerate disease spread and reduce foliage availability per larva.

Spinning and cocoon harvesting 🔗

When larvae are ready to spin, they are moved to indoor mounting structures. Indian Culture describes the traditional mounting device as a jali, constructed from dry leaves of azar or singari. The Central Silk Board recommends bamboo box-type mounts with a capacity of approximately 1,500 worms per mount. These mounts are kept in a semi-dark, well-aerated, and rodent-proof room to ensure proper cocooning and reduce post-spinning losses.

Harvesting is timed precisely. Cocoons should be harvested only after complete pupation – on the 7th day in summer and the 10th day in winter, as per the Central Silk Board guidelines. Harvesting too early risks damaging the pupa; waiting too long risks the moth emerging and breaking the silk filament.

Sorting and grading cocoons 🔗

After harvesting, cocoons are sorted into categories: good-quality cocoons, flimsy cocoons, and Uzi-fly-infested cocoons. Good cocoons are further divided based on their end use. Seed cocoons – the best-quality cocoons selected from what is called the bharpok stock on the peak day of harvest – are kept for breeding. They are placed in bamboo cages, allowed to produce moths, and the mating pairs lay eggs to continue the rearing cycle. This seed cocoon selection is one of the most critical quality-control steps in the entire system, as the genetic quality of seeds directly affects the productivity of subsequent crops.

Cocoons destined for silk production go through boiling in alkaline solution to soften the sericin (natural gum) and make the fibre reel-able. Traditional reeling is done using a wooden apparatus called a bhir or bhowri, producing a yarn with fewer twists and therefore a more lustrous finish. It takes approximately 1,000 cocoons to produce just 125 grams of silk – a yield that underscores just how labour-intensive and precise every stage of this process must be.

Challenges and the path forward 🔗

Despite the sophistication of traditional practices, Muga sericulture faces mounting pressures. Deforestation of Som and Soalu trees, unpredictable rainfall linked to climate change, rising pest and disease incidence, and the decline of younger skilled rearers all threaten the industry’s future. The Muga silkworm is also extremely sensitive to pollution, which further restricts where and how it can be reared.

On the scientific front, research into hybridization between wild and cultivated Muga populations is promising. Studies have shown that wild Muga silkworms produce heavier cocoons and exhibit greater disease resistance, particularly to protozoan infections – suggesting that targeted breeding programs could yield more resilient, productive strains. The Journal of Experimental Agriculture International notes that breeding programs combining wild and semi-domesticated populations could enhance cocoon yield, silk quality, and disease resistance simultaneously.

Muga silk received its Geographical Indication (GI) tag in 2007, and the Central Silk Board of India has been authorized to certify authentic Muga products. This recognition has helped protect the product’s identity in domestic and international markets – though challenges around counterfeiting and market access persist.

What do you think? Given that indoor chawki rearing consistently improves survival and cocoon quality, what barriers might prevent small-scale farmers from widely adopting it? And with Muga silk being tied so closely to specific tree species and regional climates, how do you think the industry should respond to the long-term threat of deforestation and habitat loss?

References

1. https://en.wikipedia.org/wiki/Muga_silk
2. https://silks.csb.gov.in/baksa/rearing-of-muga-silkworm/
3. https://indianculture.gov.in/stories/muga-silk
4. https://kilchu.com/blogs/projects-at-kilchu/muga-silk-of-assam-the-golden-treasure-of-india
5. https://www.researchgate.net/publication/371305300
6. https://sericulture.assam.gov.in/portlet-innerpage/cultivation-of-som-and-soalu
7. https://silks.csb.gov.in/majuli/rearing-of-muga-silkworm/
8. https://www.agriscigroup.us/Agricultural-Science-Food-Technology/IJASFT-1-106.php
9. https://www.researchgate.net/publication/391878904
10. https://silks.csb.gov.in/keonjhar/rearing-of-muga-silkworm/
11. https://journaljeai.com/index.php/JEAI/article/view/2117