Managing Major Pests in Eri Silkworm Host Plants

Eri silkworm (Samia ricini) farming is a cornerstone of non-mulberry sericulture across northeastern India, and its success depends entirely on the health of its host plants – especially castor (Ricinus communis). According to the Government of Assam’s Handloom Textiles & Sericulture Department, castor is the primary food plant of the eri silkworm, making its protection from pests a direct priority for silk yield and quality. When pest populations go unchecked on castor and other host plants, the consequences ripple through the entire eri rearing cycle – from leaf availability to cocoon weight. Three pests in particular – the Hairy Caterpillar, the Semi-looper, and Thrips – are responsible for the most significant foliage damage in eri silkworm plantations.

Why eri silkworm host plants are pest-prone 🔗

The eri silkworm is polyphagous in nature and can feed on over 30 species of host plants, though castor remains the most preferred and commercially important. Castor’s broad, nutrient-rich leaves are highly attractive to a wide range of insect pests. The plant’s relatively large leaf surface area provides ample space for colonisation, egg-laying, and larval feeding. Because eri sericulture depends on a steady, high-quality supply of these leaves, even moderate pest pressure can disrupt rearing schedules and reduce silk output. Recognising the three major pest threats – and knowing how to respond – is essential for every eri farmer.

Hairy caterpillar (Euproctis lunata) 🔗

The Hairy Caterpillar, Euproctis lunata, is one of the most damaging defoliators of castor. First described by Francis Walker in 1855, this moth belongs to the family Erebidae and is widely distributed across India, Pakistan, Sri Lanka, and Thailand. Its common name comes from the dense covering of barbed hairs that protect the larvae from predators – and make them a hazard to handle directly.

Identification and damage 🔗

The larvae are easily identified by their hairy, grayish-brown bodies with tufted hairs arranged along the length. Studies on the biology of E. lunata show that the pest completes six larval instars, with full-grown larvae reaching about 35 mm in length. Eggs are laid in clusters on the undersides of leaves and covered with light brown hairs; incubation lasts five to ten days. Young larvae begin by scraping the leaf surface in groups, while older caterpillars consume entire leaves – leaving behind only the main veins and midribs. Research shows that infestations peak during September and October, with yields significantly reduced when two or more larvae are present per plant. Complete defoliation weakens host plants and removes the leaf supply needed for active silkworm rearing batches.

Management of hairy caterpillar 🔗

Early-stage management is most effective. Mechanical removal – hand-picking egg masses and young gregarious larvae from infested branches – is a practical first step, though workers must use protective gloves due to the irritating larval hairs. The Tamil Nadu Agricultural University recommends spraying neem seed kernel extract (NSKE) at 5%, or applying chlorpyrifos at 2.5 ml per litre or quinolphos at 2 ml per litre of water to control early-stage larvae. Light traps can be used to monitor and trap adult moths during outbreak periods. Sanitation – removal of fallen leaves and crop debris – also helps eliminate pupae that overwinter in plant litter.

Semi-looper (Achaea janata) 🔗

The castor semi-looper, Achaea janata, is another serious defoliator of eri silkworm host plants. This erebid moth is widely distributed across tropical and subtropical regions, and is considered a significant pest of castor across the Indian subcontinent. The pest gets its common name from the way its larvae move – arching the body into a distinctive looping shape as they crawl, owing to the absence of some abdominal prolegs.

Identification and damage 🔗

The larvae are typically green or brown with longitudinal lines running along the body, growing to 5-6 cm when fully mature. Females lay pale green, hemispherical eggs on the undersides of leaves. Seasonal outbreaks are most common from July to September, with the entire life cycle from egg to adult completed in about 48 to 50 days – allowing multiple generations to build up rapidly in a single season. During population outbreaks, larvae feed gregariously and strip foliage quickly, leaving only midribs and veins intact on affected plants. The damage reduces the photosynthetic capacity of castor and in severe cases causes young plants to wilt entirely.

Management of semi-looper 🔗

Control strategies for A. janata combine mechanical, biological, and chemical methods. Hand-picking of late-instar larvae and the use of pheromone traps and light traps are effective for adult management. For biological control, the egg parasitoid Trichogramma evanescens is known to destroy eggs, while Microplitis maculipennis parasitises caterpillars. Neem seed kernel extract sprays are specifically recommended to destroy eggs on the plant surface. For chemical control, sprays of quinalphos, chlorpyrifos, or carbaryl can be applied when populations cross economic threshold levels. Studies have also confirmed the efficacy of Bacillus thuringiensis (Bt) formulations against the castor semi-looper, making it a viable option within integrated pest management (IPM) programmes.

Thrips (Astrothrips parvilimbus) 🔗

Unlike the defoliating caterpillars above, Astrothrips parvilimbus is a piercing-sucking pest that damages castor and other eri host plants by extracting sap and cellular contents directly from leaf tissue. While individual thrips are small – typically just 1 to 2 mm long – infestations can cause widespread and cumulative leaf damage that significantly affects leaf quality for silkworm rearing.

Identification and damage 🔗

Thrips are slender, dark-coloured insects that are difficult to see with the naked eye but leave distinctive signs of their feeding. Affected leaves develop a silvery or bronze discolouration, caused by the collapse of chlorophyll-containing cells at feeding sites. Closer inspection reveals tiny white or pale feeding punctures that merge into larger damaged patches over time. Heavily infested leaves may curl, distort, or drop prematurely, reducing both the quantity and quality of foliage available for eri silkworms. Because thrips tend to shelter in leaf folds and new growth, populations can build up quickly before the damage is noticed.

Management of thrips 🔗

For thrips management in eri host plant gardens, a combination of cultural and chemical measures is recommended. Maintaining proper plant spacing improves air circulation and reduces the humid microenvironments where thrips thrive. Removing and destroying heavily infested leaves early limits the spread of populations within a planting. For chemical control, systemic insecticides – those absorbed by the plant and delivered through the sap – provide longer-lasting protection than contact sprays alone, since thrips often hide in protected plant tissue. Neem-based formulations, particularly neem oil and azadirachtin-based products, are effective and environmentally safer options. Azadirachtin at 5% w/w neem extract concentrate applied at the recommended rate is used against early instar larvae of sucking and chewing pests on castor, and the same approach is applicable for thrips management on eri host plants.

Integrated and eco-friendly management strategies 🔗

Given that eri silkworm farming is closely tied to the leaves harvested from these host plants, it is important that pest management does not leave residues that could harm the silkworms themselves. This is why neem-based treatments have become a preferred approach in eri sericulture. Neem seed kernel extract sprays are widely recommended because they act as antifeedants, disrupt insect development, and are biodegradable – breaking down relatively quickly without accumulating in the plant tissue. Research has confirmed that neem acts as a feeding deterrent against both Achaea janata and hairy caterpillars, reducing damage without the residue risks of synthetic chemicals.

Beyond direct pest control, a few broader practices make a significant difference. Regular field monitoring – especially during the peak infestation months of July to October – allows for early detection and timely action before populations build to damaging levels. Collecting and destroying egg masses before hatching prevents the gregarious early instars from establishing. Maintaining field hygiene by clearing fallen leaves and plant debris removes overwintering sites for multiple pests simultaneously. Where possible, crop rotation with non-host plants for one or two seasons can help break the pest cycle in persistently infested areas. For chemical sprays, rotating between insecticide classes prevents the development of resistant pest populations over successive seasons.

The Central Muga Eri Research and Training Institute (CMERTI), under India’s Central Silk Board, provides technical guidance on eri host plant cultivation and management, and is a valuable resource for farmers looking to maintain pest-free plantations in line with current recommendations for ericulture.

What do you think? With eri sericulture farmers needing both effective pest control and residue-free leaves for their silkworms, how should they decide when to use chemical sprays versus neem-based treatments? And as pest pressure on castor increases in changing climatic conditions, could promoting alternative eri host plants like kesseru or cassava help reduce the overall pest burden on ericulture operations?

References

1. https://hts.assam.gov.in/portlet-innerpage/host-plants-of-eri-silkworm
2. https://www.researchgate.net/publication/374157120_Breeding_in_Host_Plants_of_Eri_Silkworm_for_Rearing_Suitability
3. https://en.wikipedia.org/wiki/Euproctis_lunata
4. https://www.indianjournals.com/article/ijfs-6-3-024
5. https://www.sciencedirect.com/science/article/abs/pii/0261219488900816
6. https://agritech.tnau.ac.in/crop_protection/castor/crop_prot_crop_insect_oil_castor_5.html
7. https://en.wikipedia.org/wiki/Achaea_janata
8. https://farmonaut.com/precision-farming/castor-semilooper-larvae-identifying-and-managing-this-destructive-pest-in-your-crop-fields/
9. https://www.studyandscore.com/studymaterial-detail/pest-of-oil-seed-achaea-janata-distribution-life-cycle-nature-of-damage-and-control-measures
10. https://www.iaszoology.com/achaea-janata/
11. https://eurekamag.com/research/002/302/002302740.php
12. https://www.slideshare.net/slideshow/castor-ipm-integrated-pest-management-by-manish-jindal/270685022
13. https://cmerti.res.in/faq/