Best Practices for Late Age Silkworm Rearing Methods

The third, fourth, and fifth instar larvae – collectively called late age silkworms – are the most demanding phase of the entire rearing cycle. These worms consume roughly 85% of their total food requirement during the fifth instar alone, and about half of all the labour input in a rearing cycle is concentrated in the final seven days. Getting the rearing method right during this phase isn’t just a matter of convenience – it directly determines cocoon quality and your overall yield. Sericulturists across India and beyond use three main approaches: tray rearing, shelf (rack) rearing, and floor rearing. Each has a distinct set of trade-offs around space, labour, cost, and hygiene.

Why the rearing method matters in late age 🔗

Late age silkworms grow rapidly and need significantly more space, better ventilation, and higher quantities of fresh mulberry leaf or shoot with every passing day. Maintaining a temperature of 23-25°C and a relative humidity of 65-70% is considered optimal for this stage, as higher humidity combined with high temperature creates conditions favorable to pathogen outbreaks. Beyond environment, the physical setup – how worms are housed and fed – shapes how well these conditions can actually be maintained. The choice of method also affects how much labour, capital, and floor space a farmer needs to commit.

The three methods of late age rearing are selected based on space availability, economic condition of the farmer, and availability of labour. Understanding what each method involves helps farmers match it to their specific situation.

Tray rearing 🔗

Tray rearing is the most widely practiced method among small-scale and marginal farmers in India, particularly in Karnataka and West Bengal. Silkworms are reared in bamboo or wooden trays arranged one above the other in tiers on rearing stands, which can hold 10 to 12 tiers. The compact, vertical arrangement makes this method practical for farmers who operate out of rearing-cum-dwelling houses where floor space is limited.

How it works 🔗

Feeding is done 3-4 times every day, and cleaning of the rearing bed – removing old leaves and litter – is carried out daily using nylon nets of mesh size 2″ × 2″. Newspapers are commonly spread in the trays to absorb excess moisture from leaves and faecal pellets. The larvae are fed chopped mulberry leaves, and the bed area is expanded at each instar to match the growing worms.

Advantages and limitations 🔗

The biggest strength of tray rearing is precision. It offers close control over feeding quantities, larval density, and early detection of disease. Conventional round bamboo trays are light and easy to handle individually, which makes monitoring straightforward. However, the method is labour-intensive – daily bed cleaning, frequent leaf plucking, and the physical handling of many trays throughout the day add up. This makes it less economical when scaled up. Frequent tray handling also risks stressing the worms if not done carefully. Still, for farmers with limited space and smaller batches, tray rearing remains a practical and widely trusted option.

Shelf (rack) rearing 🔗

Shelf rearing – also called rack rearing – takes the same vertical-tier concept as tray rearing but replaces the chopped-leaf feeding method with whole mulberry shoots placed directly on the racks. This one shift in feeding strategy dramatically changes the workload. Shoot rearing saves labour by up to 70% compared to leaf feeding when measured on an hour-to-hour basis, and reduces leaf consumption by 15-20%.

Setup and structure 🔗

A standard rearing rack of 1.2 m × 11 m is sufficient to rear 50 disease-free layings (dfls). The shelves are arranged in a three-tier system with 50 cm of space between tiers, and a 15 cm border is provided on all sides of each shelf to prevent larvae from migrating. Rack stands are fabricated from wood or steel, with rearing seats made from wire mesh or bamboo mat. The recommended total rack height of 6-7 feet ensures adequate headroom for feeding and monitoring, while keeping the bottom tier at least one foot above the ground.

Feeding and bed cleaning 🔗

Big shoots harvested from the field are fed directly to the worms. The top and bottom ends of the shoots are placed alternately across the bed width to ensure even distribution of leaf quality. This is a key detail – older leaves towards the base and tender leaves at the tip are mixed so all worms get a balanced feed. Third instar larvae are transferred to the shoots immediately after moulting.

Bed cleaning in shelf rearing is considerably less frequent than in tray rearing. Cleaning is done once during the second day of the fifth instar using either a rope method or a net method. In the net method, a 1.5 cm² size net is spread across the bed; after two or three feedings, larvae migrate upward through the net onto fresh shoots, and the old bed beneath is cleaned and disinfected. This system keeps silkworms away from litter, significantly reducing the risk of secondary contamination.

Why it works well for medium-scale operations 🔗

Shelf rearing also results in better cocoon characters and effective rate of rearing (ERR), better preservation of leaf quality on the bed, and more organic matter production – up to 18 tonnes per hectare per year. Because silkworm handling is minimised, contamination and disease spread are reduced. The main drawback is that shelf rearing needs about 30% more floor area than tray rearing, and bed refusals from shoot feeding are not useful as cattle feed.

Floor rearing 🔗

Floor rearing is the most traditional of the three methods and is practised extensively in Kashmir and some parts of China. It involves rearing directly on the floor of the rearing house using mulberry shoots or branches, without any tray or rack infrastructure.

How it is set up 🔗

A rearing bed of 5 feet in width and as long as the rearing room is prepared on either side of the floor on old newspapers. Before the newspaper is spread, a thin layer of lime is dusted on the floor to prevent ant attack. Feeding follows the shoot feeding method used in shelf rearing, and no bed cleaning is required during the rearing cycle. The silkworms feed and grow naturally on the spread shoots without being disturbed by routine cleaning.

Hygiene and economics 🔗

Floor rearing stands out on two fronts: cost and cleanliness. Since no rearing racks are used, the method is highly economical and hygienic. The newspaper layer absorbs excess moisture and can be replaced as needed, removing waste and preventing the build-up of pathogens. There is no investment in stands, trays, or racks, making it accessible to farmers with minimal capital. The relatively wide bed spread also means worms have ample room and better natural airflow compared to the tightly stacked trays of the tray rearing method.

The limitation is space. Floor rearing requires the most floor area of the three methods – the entire usable floor of the rearing house is occupied by rearing beds on both sides, leaving only a narrow central passage. For farmers with large, purpose-built rearing rooms, this is manageable. For those rearing in shared spaces, it may not always be feasible.

Comparing the three methods 🔗

Each method serves a different type of farmer and operational scale. Tray rearing is best suited for small-scale or marginal farmers operating in limited space who want close control over their batches. Shelf rearing works well for medium-scale rearers who can invest in rack infrastructure and have a reliable shoot supply, since the labour savings are substantial over repeated rearing cycles. Floor rearing is ideal where space is available, capital is limited, and a simple, low-maintenance system is preferred.

It is also worth noting that the Central Sericultural Research and Training Institute (CSR&TI) has developed and promoted shoot rearing as a standard practice for late age worms because of its combined advantages in labour saving, leaf efficiency, and cocoon quality – benefits that apply to both shelf and floor rearing when shoots are used as the feeding method.

Some experienced farmers combine methods across rearing cycles – using tray rearing for smaller premium batches and floor or shelf rearing for bulk production. The environmental conditions of a region also play a role: in high-humidity areas, shelf or floor rearing’s better air circulation can be an important factor in keeping diseases under control.

Key environmental requirements across all methods 🔗

Regardless of which rearing method is chosen, certain environmental standards apply universally to late age rearing. Temperature should be maintained between 23-28°C, and relative humidity kept in the 65-70% range for superior cocoon quality. Bed disinfectants such as TNAU Seridust, Resham Jyothi, or Vijetha are applied at recommended quantities after each moult, with a total application of 4 kg per 100 dfls across all moults. Good ventilation, avoidance of direct strong light, and strict hygiene at entry points of the rearing house are non-negotiable practices regardless of the method in use.

What do you think? Given the trade-offs between labour, space, and cost in each method, which approach do you think would be most sustainable for small-scale sericulture farmers in regions with high humidity and limited land – and how might climate variability affect that choice in the long run?

References

1. https://agritech.tnau.ac.in/sericulture/seri_silkworm4_lateage%20rearing.html
2. https://wikifarmer.com/library/en/article/silkworm-management-housing-and-nutrition
3. https://egyankosh.ac.in/bitstream/123456789/9169/1/Unit-3.pdf
4. https://nif.org.in/innovation/silk_worm_rearing_tray/255
5. https://feedsfree.com/silkworm-rearing-house/
6. https://silks.csb.gov.in/biswanath/rearing-of-mulberry-silkworm/