Pest Control in Muga Silkworm Host Plants: Key Strategies

Muga silk – prized for its natural golden sheen and exceptional durability – is produced by the semi-domesticated Antheraea assamensis silkworm, found primarily in Assam and parts of northeastern India. The silkworm depends almost entirely on two host plants: som (Persea bombycina) and soalu (Litsea polyantha). The health of these plants directly determines the quality and quantity of silk produced. Yet these plants face relentless attacks from a set of specific pests – each capable of causing serious damage if left unchecked. Understanding what these pests are, how they damage host plants, and how to manage them is central to sustaining a productive muga sericulture system.

Why host plant health is critical in muga sericulture
Major pests of muga silkworm host plants
Amphutukani – Cricula trifenestrata
Aphids – Aphis craccivora
Stem borers – Zeuzera multistrigata
Pest management strategies
Managing Amphutukani (Cricula trifenestrata)
Managing aphids (Aphis craccivora)
Managing stem borers (Zeuzera multistrigata)
General preventive and sanitation practices

Why host plant health is critical in muga sericulture

Research on muga host plant management consistently points out that the occurrence of pests in host plants deteriorates leaf quality, which in turn directly affects silkworm health and the quantity of raw silk produced. Since muga silkworms are reared outdoors on living trees – not in controlled facilities – their food source is permanently exposed to the natural environment and, with it, a range of insect pests. Protecting som and soalu from pest damage is therefore not just a plant health concern; it is the foundation of the entire muga silk production chain.

Major pests of muga silkworm host plants

Three pests are of primary concern in muga host plant management: a competing defoliating caterpillar, a sap-sucking aphid, and a stem-boring moth. Each attacks the plant in a different way and requires a different control response.

Amphutukani – Cricula trifenestrata

Amphutukani (locally called Amphutukoni muga) is the common name for Cricula trifenestrata Helfer, a wild saturniid silkmoth whose larvae are among the most destructive pests of muga host plants. According to research published in the Bulletin of the National Research Centre, this insect depletes the foliage of host plants, directly affecting the Effective Rearing Rate (ERR) of the muga silkworm. The problem is compounded by the fact that Cricula feeds on the very same plants – including Persea bombycina – that muga silkworms depend on, making it a direct competitor for food.

The larval feeding pattern is particularly damaging. Studies on its life history and population growth show that the caterpillar’s last instar stage alone accounts for consuming 69-72% of its total food intake, with the final three instars together consuming 95-97% of total intake. In severe infestations, caterpillars devour the entire leaf blade except the midrib, giving the plant a characteristic broom-like appearance. This destruction reduces the available foliage for muga silkworms during commercial rearing seasons.

Cricula trifenestrata is a gregarious feeder – larvae move together and can strip branches rapidly. It is also documented as a migratory pest, moving from one location to another as food availability changes, which makes infestations harder to predict and control. The pest completes 4-5 life cycles per year under natural conditions, meaning pressure on host plants persists across multiple muga rearing seasons.

Aphids – Aphis craccivora

Aphids (Aphis craccivora Koch) are soft-bodied, sap-sucking insects that attack the tender leaves and young shoots of som plants. They are small – typically 1.4-2.2 mm – but form dense colonies on growing points of plants. According to CABI’s invasive species profile, young colonies typically concentrate on growing points and are often tended by ants, which protect them from natural enemies in exchange for honeydew secretions.

Field studies on aphid infestation of som plants reveal that peak populations occur between the second week of September and the first week of October, with average populations reaching nearly 25 aphids per leaf during this period. A secondary spike also occurs in January-February. The feeding damage manifests as curling and puckering of young leaves, yellowing, wilting, and stunted shoot growth. Beyond direct feeding damage, the honeydew secretions from aphids attract saprophytic fungi, which can lead to widespread fungal infestation and stem rotting – extending the damage well beyond what the insects themselves cause. Since the leaves of som are the primary food source for muga silkworms, any reduction in leaf quality or availability translates directly into poor cocoon production.

Stem borers – Zeuzera multistrigata

The carpenter moth, Zeuzera multistrigata Moore (Lepidoptera: Cossidae), commonly called the stem borer, poses a structurally different and particularly serious threat to muga host plants. As reviewed in the Indian Journal of Pure and Applied Biosciences, stem borers bore into the stems and trunks of som and soalu plants, feeding on internal tissues – particularly the xylem and phloem – that transport water and nutrients throughout the plant. As the internal tunnels expand, the structural integrity of the main trunk weakens, and in severe infestations, the tree dies.

What makes this pest especially difficult to manage is that the larvae complete most of their life cycle inside the tunnel, hidden from view. Research from the Central Silk Board’s Muga Eri Silkworm Seed Organisation describes the adult moth as having a distinctive black head and antennae, with a thorax bearing three pairs of blue-white spots. The female lays eggs underneath bark or around tunnel entrances; upon hatching, larvae immediately begin feeding on phloem tissue before boring deeper into the wood. Because the larvae migrate between trees during their development, even a small population can cause significant plantation damage.

External signs of infestation include small circular bore holes in the bark – approximately 0.6-0.9 cm in diameter – accompanied by sawdust-like frass around entry points. Affected plants may show wilting, yellowing, or stunted growth even when growing conditions appear otherwise favourable. Field surveys on Zeuzera multistrigata across different host species confirm that heavily attacked trees show declining health and vigor, with many eventually suffering broken stems.

Pest management strategies

Controlling these three pests requires an integrated approach combining chemical, mechanical, and preventive measures. Critically, because muga silkworms are reared directly on the same plants, any chemical treatment must be carefully timed to prevent harm to the silkworms themselves.

Managing Amphutukani (Cricula trifenestrata)

Both chemical and mechanical methods are used against Cricula. According to the Central Silk Board’s muga food plant production guidelines, spraying 0.05% Phosphomidon effectively controls the pest. Mechanical control is equally important: hand-collecting and destroying caterpillars and egg masses from infested branches reduces populations significantly. Cocoons of Cricula found on the host plants should be collected and burnt to prevent further multiplication. Since both Cricula and the muga silkworm are saturniid insects, care must be taken to avoid applying insecticides when muga silkworms are actively feeding on the plants.

Managing aphids (Aphis craccivora)

For aphid control, established pest management protocols for muga food plants recommend spraying systemic insecticides such as Rogor, Ekalux, or Anthio at a 5% solution using a low-volume sprayer applied to the foliage. However, treated plants must not be used for muga silkworm feeding for the specified post-spray waiting period. An important alternative is the use of bio-pesticides. Research comparing synthetic and botanical treatments on aphid-infested som plants found that while imidacloprid provided over 80% aphid suppression, the botanical insecticide azadirachtin and extracts of Polygonum hydropiper also achieved meaningful control (over 60% suppression) without the risks that synthetic insecticides pose to the muga silkworm. Since som leaves are the direct food source for the silkworm, bio-pesticides that have little or no hazardous effect on the silkworm are strongly preferred where feasible. Physically removing and destroying curled leaves harbouring aphid colonies also helps reduce spread.

Managing stem borers (Zeuzera multistrigata)

Stem borers are the hardest of the three pests to control because they are largely hidden inside plant tissue once established. The Central Silk Board’s production guidelines recommend a targeted fumigation method: plugging the larval entry holes with cotton balls soaked in a 1.5% Nuvan solution, followed by plastering the hole with mud to seal in the fumes. This delivers the insecticide directly to the larvae inside the tunnel. Conventional contact insecticides sprayed on the bark surface are generally ineffective once borers are inside the stem. Additional fumigant chemicals such as chloroform or benzene applied via cotton wool plugging have also been reported as effective. Early intervention before larvae bore deep is important: spraying insecticides on bark surfaces when adult moths are laying eggs – typically identified through monitoring – can reduce larval establishment. Mechanically removing and burning severely infested branches helps limit the spread of the infestation across the plantation.

General preventive and sanitation practices

Across all three pests, field sanitation plays a foundational role. Regular removal and destruction of infested leaves, egg masses, and branches eliminates pest breeding sites and reduces the overall pest load in the plantation. Monitoring the plantation consistently – especially during peak infestation periods for each pest – allows farmers to act before populations reach damaging levels. For stem borers, checking bark surfaces for bore holes and frass accumulation, and tapping suspected areas to detect hollow sounds, helps detect infestations early. Maintaining healthy, well-nourished plants also improves their natural resistance to pest damage. And since muga silkworm rearing is conducted outdoors on the same plants, every pest management decision must account for silkworm safety – treated trees must always observe an adequate waiting period before being used for rearing again.

What do you think? Given that muga silkworms feed on the same plants targeted for pest control, how should farmers balance the need for effective chemical treatment with the safety of the silkworms? And with bio-pesticides showing promising results against aphids on som plants, could expanding their use across all three pest types become a practical strategy for muga sericulture farmers?

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Table of Contents

Why host plant health is critical in muga sericulture 🔗

Major pests of muga silkworm host plants 🔗

Amphutukani – Cricula trifenestrata 🔗

Aphids – Aphis craccivora 🔗

Stem borers – Zeuzera multistrigata 🔗

Pest management strategies 🔗

Managing Amphutukani (Cricula trifenestrata) 🔗

Managing aphids (Aphis craccivora) 🔗

Managing stem borers (Zeuzera multistrigata) 🔗

General preventive and sanitation practices 🔗