Ensuring Optimal Mulberry Leaf Quality and Quantity for Late Age Silkworms

In sericulture, the difference between a mediocre cocoon harvest and an exceptional one often comes down to one variable: the quality and quantity of mulberry leaves fed to silkworms during their final growth stages. Late age silkworms – those in the fourth and fifth instars – are the most demanding feeders in the entire rearing cycle. According to the FAO, the quality and quantity of mulberry leaf produced per unit area have a direct bearing on cocoon harvest. Getting this right is not optional – it is the foundation of profitable silk production.

Why leaf quality matters most in the late age period 🔗

Silkworms pass through five larval stages, called instars, before spinning their cocoons. The first three instars are relatively low-demand phases. It is in the fourth and fifth instars – collectively referred to as the late age period – that nutritional requirements shift dramatically. Research published in the Journal of Insect Science confirms that the feed utilization study for bivoltine silkworms is most critical during the fifth instar, where environmental and nutritional conditions exert the greatest influence on silk output. During the fourth instar, silkworms consume approximately 14% of their total lifetime leaf intake. That figure jumps to 80% during the fifth instar, meaning these two stages together account for around 94% of all leaves a silkworm will ever eat. This lopsided feeding pattern has a direct implication: any shortfall or compromise in leaf quality during this window cannot be compensated for later.

The nutritional role of mulberry leaf goes beyond simply filling the silkworm’s gut. A study in PLOS ONE confirmed that the weight of fifth instar silkworm larvae increases progressively from day one to day seven, and that the ratio of silk gland weight to body weight – a direct indicator of cocoon shell quality – is significantly influenced by the nutritional composition of leaves fed during this stage. In simpler terms, the leaf determines the silk.

The ideal leaf: why shoot age is the key criterion 🔗

Not all mulberry leaves are nutritionally equivalent. The single most reliable indicator of leaf suitability for late age silkworms is the age of the shoot from which they are harvested. Leaves from shoots that are 55 to 65 days old represent the optimal window. At this age, leaves have developed the right balance of moisture, protein, and carbohydrates that late age silkworms need for rapid growth, silk gland development, and cocoon spinning.

Leaves at this stage typically measure 8 to 12 centimetres in length, have well-developed but still pliable veins, and retain the structural integrity that silkworms need to grasp and consume them efficiently. A compositional study of Morus alba leaves published in PubMed found that moisture in fresh mulberry leaves ranges from 71 to 76%, while crude protein spans 4.72 to 9.96% on a fresh weight basis – values that shift significantly with leaf maturity and position on the branch.

What to avoid: over-mature and overly tender leaves 🔗

Leaves from shoots older than 70 days become tough and fibrous. Their moisture content drops, crude protein declines, and fibre levels increase – all of which reduce digestibility and slow silkworm growth. Over-mature leaves also tend to accumulate tannins and other compounds that can inhibit feeding and development. Industry data on mulberry leaf composition shows that lower, hardened leaves have notably reduced soluble sugar content compared to middle and upper leaves – a direct drop in the carbohydrate energy available to silkworms during their most energy-intensive phase.

On the opposite end, leaves from shoots younger than 45 days are too tender. They contain excessive moisture and insufficient protein density. When fed to late age silkworms, these leaves result in poor growth rates, watery frass, and compromised cocoon quality. The silkworms consume large volumes but obtain inadequate nutrition – an inefficient and costly outcome.

Leaf position on the branch also matters 🔗

Within a single shoot, leaf position is a practical proxy for quality. Upper leaves (tender, high moisture, high protein) are best reserved for young age or chawki rearing. For late age silkworms, middle-position leaves are ideal – they carry higher dry matter and carbohydrate content, which supports the energy demands of silk gland development. FAO documentation on mulberry utilisation confirms that for silkworm feeding, individual leaf picking and shoot harvesting methods are adapted based on the feed requirements of specific larval stages. Basal leaves, which are hardened and low in both moisture and protein, should generally be avoided for silkworm feeding altogether.

Quantifying the leaf requirement: planning ahead is essential 🔗

Late age silkworm rearing demands significant advance planning because the volume of leaves required escalates sharply from the fourth to the fifth instar. For every 100 silkworms entering the fourth instar, approximately 15 to 20 kilograms of fresh mulberry leaves are required. When those same silkworms move into the fifth instar, the requirement climbs to 80 to 100 kilograms. Research from the Department of Entomology, College of Agriculture, Parbhani confirms the high leaf demand during this phase in their experiments on late age silkworm development and leaf requirements.

Scaling up, it takes roughly one tonne of mulberry leaves to rear a single case of eggs and produce 25 to 30 kilograms of high-quality cocoons. This figure underscores why accurate leaf yield assessment and rearing schedule coordination are non-negotiable in commercial sericulture operations. Maintaining a feeding chart that tracks daily consumption against silkworm batch size and development stage helps sericulturists anticipate shortfalls before they occur.

Feeding frequency and distribution 🔗

Providing the right leaf at the right time in the right amount is the practical challenge of late age rearing. The IGNOU sericulture training module specifies that the ideal time to harvest mulberry leaves or shoots is during morning hours, when leaves hold maximum moisture and nutritional content. Leaves should be transported in bamboo baskets covered with gunny cloth, and if transport exceeds 30 minutes, the covering should be kept damp to reduce moisture loss.

Late age silkworms should be fed every 3 to 4 hours during active feeding periods, with larger quantities offered during peak feeding times. Rather than depositing leaves in a single pile, spreading them evenly across rearing trays ensures all silkworms have equal access and reduces competition stress. Leaves stored prior to feeding should be kept in a cool, well-ventilated room at high humidity, and should be used within 24 to 48 hours of harvest. Any leaves showing yellowing, browning, sliminess, or off-odours must be discarded immediately.

Adjusting leaf selection by season 🔗

Seasonal variation affects mulberry leaf quality significantly, and sericulturists must adapt their selection criteria accordingly. The Journal of Insect Science study on seasonal variation in silkworm food consumption found that leaf intake by bivoltine silkworms was lowest in summer and highest in winter, reflecting how temperature and humidity influence both leaf quality and silkworm physiology. Specifically, higher rearing temperatures in summer reduce feeding duration in the fifth instar, which adversely affects larval weight and silk output.

During spring, moderate temperatures and good humidity produce leaves with excellent moisture and balanced nutrition – the most favorable season for late age rearing. Summer accelerates leaf maturation, so harvesting frequency must increase to prevent leaves from becoming over-mature before they are used. The monsoon season introduces fungal risks and can dilute nutritional content through excess moisture; leaves should be selected from well-drained plantation areas and lightly dried before feeding. Winter leaves, while produced in smaller quantities, tend to have concentrated nutrients but can be tougher in texture – slight wilting before feeding can improve palatability without significant nutritional loss.

Staggering mulberry pruning schedules 🔗

One of the most effective long-term strategies is to stagger mulberry pruning and planting schedules so that shoots of the right age (55 to 65 days) are always ready when a silkworm batch enters the fourth instar. Rotating harvest zones across the plantation – rather than stripping a single area repeatedly – allows each section to regenerate while another is in use. This approach also prevents soil depletion and maintains consistent leaf quality across seasons. FAO’s mulberry cultivation guidelines for India recommend individual leaf harvesting as the standard practice under irrigated conditions, with pruning timed to align leaf maturity cycles with planned rearing schedules.

The direct link between leaf quality and cocoon quality 🔗

Every aspect of cocoon quality – shell weight, shell ratio, filament length, and raw silk reelability – traces back to what the silkworm ate during the fourth and fifth instars. A recent study in the Archives of Current Research International on mulberry leaf biomass and protein content confirmed that mulberry leaf protein and moisture are primary determinants of silkworm growth, cocoon yield, and raw silk quality. The silk proteins fibroin and sericin, which form the cocoon shell, are built almost entirely from amino acids derived from mulberry leaf protein. A leaf deficit – whether in quantity or quality – during the fifth instar directly translates to a lighter, thinner cocoon with less reelable silk.

This is why sericulturists who invest in proper mulberry garden management, timely harvesting, and disciplined feeding schedules consistently outperform those who treat leaf supply as an afterthought. The rearing house is only as productive as the garden that feeds it.

What do you think? Given that 80% of leaf consumption happens in just the fifth instar, how would you redesign your mulberry plantation layout to ensure a consistent supply of 55-65-day-old shoots at exactly the right time? And do you think seasonal adjustment of leaf maturity criteria is given enough attention in standard sericulture training programs?

References

1. https://www.fao.org/4/x9895e/x9895e04.htm
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC3596942/
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC10585384/
4. https://pubmed.ncbi.nlm.nih.gov/17135021/
5. https://www.pandasilk.com/quality-of-mulberry-leaves/
6. https://www.fao.org/4/x9895e/x9895e0t.htm
7. https://www.researchgate.net/publication/385320536_Evaluate_the_requirement_of_mulberry_leaf_for_the_development_of_late_age_silkworm_and_nutrient_status_of_seri-waste
8. https://egyankosh.ac.in/bitstream/123456789/9169/1/Unit-3.pdf
9. https://journalacri.com/index.php/ACRI/article/view/1815