Effective Pest Control for Muga Silkworms

Muga silkworms (Antheraea assamensis Helfer) are the source of India’s prized golden silk, found almost exclusively in Assam and the surrounding northeastern states. Unlike mulberry silkworms reared indoors, muga silkworms are semi-domesticated and raised outdoors on som (Persea bombycina) and soalu (Litsea polyantha) trees throughout six crop cycles a year. This open-air rearing system, while natural, exposes the silkworms to a continuous threat from insect pests. Pest damage during preseed and seed crop cycles can be especially severe, making effective pest management one of the most critical factors in maintaining the quality and quantity of muga silk output.

Why pest pressure is a persistent challenge in muga rearing 🔗

Because muga silkworms are reared outdoors year-round, they are constantly exposed to natural predators and parasitoids. Research conducted at the Central Silk Board’s Muga Silkworm Seed Organization in Narayanpur, Assam identified at least nine insect pest species belonging to six families – including Tachinidae, Braconidae, Formicidae, Pentatomidae, Vespidae, and Mantidae – infesting the silkworm under field conditions. Pest losses are heaviest during the preseed crops (Aherua and Jarua) and seed crops (Chotua and Bhodia), compared to the main commercial crops (Jethua and Kotia). Controlling these pests is complicated further by the fact that conventional chemical insecticides cannot be used in muga rearing because they are toxic to the silkworms themselves, making non-chemical and integrated strategies the only viable path.

Major pests of muga silkworms 🔗

Uzi fly (Exorista sorbillans) 🔗

The uzi fly is the single most damaging pest in muga sericulture. Among all pests, the uzi fly is an economically significant endo-larval parasitoid responsible for a 15% to 20% yield loss. It is a dipteran endoparasitoid belonging to the family Tachinidae. The adult female lays eggs directly at the intersegmental region of 4th and 5th instar larvae. Once the eggs hatch, the maggots burrow into the larval body and feed on the internal tissues and fat bodies. The silkworm larvae parasitized at early stages are killed before they can spin, while those parasitized at later stages spin weak, pierced cocoons that are unfit for reeling, drastically reducing their market value. Attack by uzi fly is most severe during the Jarua (December-January) and Chotua (February-March) crop seasons.

Ants (Oecophylla smaragdina) 🔗

The red weaver ant, Oecophylla smaragdina, is among the most persistent and widespread predators of muga silkworms. A field survey across Jorhat and Lakhimpur districts of Assam found 100% ant infestation during muga silkworm rearing, with Oecophylla smaragdina emerging as the most frequently observed and predacious species, particularly targeting early larval instars. Peak predation was recorded during the Aherua (June-July) crop cycle, with estimated losses ranging between 1% and 25%. These ants build nests directly in the host trees where silkworms feed, constructing leaf shelters and establishing foraging trails that lead directly to the larvae. Workers communicate through chemical signals to recruit more colony members when a food source – such as a cluster of young larvae or egg batches – is located. Weaver ants are highly territorial and workers aggressively defend their territories, making them difficult to displace once established on a rearing tree.

Apanteles parasitoids (Apanteles glomeratus) 🔗

Apanteles glomeratus, a braconid wasp, is a formidable internal parasitoid of muga silkworm larvae. Primary insect pests of muga silkworm include Apanteles glomeratus (Braconid fly) alongside the uzi fly, ants, and wasps. Female Apanteles wasps use a needle-like ovipositor to inject eggs directly into the body of the silkworm larva. The larvae that hatch inside feed on the host’s tissues, initially allowing the host to continue feeding and developing. Over time, however, the parasitized larva shows signs of stunted growth, reduced appetite, and abnormal behaviour. When the internal parasitic larvae are ready to pupate, they exit the host’s body – killing it in the process – and spin tiny yellow cocoons on the outside. A single silkworm may be parasitized by multiple Apanteles larvae simultaneously, leading to high mortality rates within a rearing batch.

Wasps (Vespa orientalis and related species) 🔗

Wasps are active predators of muga silkworm larvae and present a particularly acute threat during the summer and monsoon crop cycles. The wasp Vespa orientalis causes around 20% damage during the Aherua (May-June) and Bhodia (August-September) crop seasons. These wasps directly attack larvae, dismember them, and carry pieces back to their nests to feed their own brood. Because they are fast-moving and can repeatedly return to the same rearing trees, their impact can be rapid and severe over a short period. Other predatory insects that threaten silkworms include stink bugs, praying mantis (Hierodula bipapilla), and reduviid bugs (Sycanus collaris).

Other minor predators 🔗

Beyond the major pests, muga silkworms are also targeted by a range of minor insect predators. Stink bugs (family Pentatomidae) pierce the larval body and suck out body fluids, causing localised damage to larvae. Praying mantises are opportunistic predators that capture and consume silkworm larvae whenever they are within reach on host plant branches. Earwigs and dermestid beetles have also been observed attacking silkworms in the rearing environment, though with less frequency and intensity than the primary pest species.

Management strategies for muga silkworm pests 🔗

Because chemical pesticides are ruled out in muga rearing due to their direct toxicity to silkworms, management relies on manual, cultural, biological, and integrated approaches. Each pest requires a tailored strategy.

Manual and mechanical control 🔗

Manual methods are among the most practical first-line interventions in field conditions. Covering silkworms with nylon nets during peak uzi fly infestation periods (December to March) ensures 80-90% control. Fly eggs visible on the integument of late-stage larvae can be carefully removed using forceps during transfer operations. Uzi-infested worms should be mounted separately on jali (mountage) to prevent spread, and uzi maggots that emerge from the cocoons within three days of spinning should be collected and destroyed. For cocoon protection, stifling (killing the pupa inside) within two to three days of spinning helps eliminate any maggots still inside. Wasp traps placed around the rearing trees can help reduce the local wasp population during high-activity periods.

Cultural control 🔗

Cultural practices aim to reduce pest populations and create a less favourable environment for them. Ploughing or digging the soil in rearing plots exposes uzi fly maggots and pupae to natural predators and direct sunlight, reducing infestation levels. Avoiding continuous rearing from December to April limits the build-up of uzi fly populations in the rearing area. Keeping the rearing environment clean and free from weeds, debris, and decaying organic matter reduces nesting opportunities for ants and wasps. Ant colonies on host trees can be disrupted by applying sticky substances (such as grease bands) around the base of tree trunks and on branches, physically blocking their access routes to the silkworms. Harvesting cocoons promptly and not leaving them exposed on the trees also reduces predation risk from wasps.

Biological control 🔗

Biological control – using natural enemies of the pests – offers an environmentally sound alternative in muga sericulture. The inundative release of the pupal parasitoid Nesolynx thymus Girault (Hymenoptera: Eulophidae), a hyperparasitoid of the uzi fly, has been recommended to reduce uzi fly populations in muga rearing fields. This method targets the pest specifically without any risk to the silkworms themselves. Research into further biological agents that target Apanteles and wasp populations is ongoing. Importantly, biopesticides such as Bacillus thuringiensis are prohibited in northeastern sericulture areas because they are highly toxic to silkworms, reinforcing the need for strictly silkworm-safe biocontrol strategies.

Integrated pest management (IPM) 🔗

Integrated pest management combines the strengths of manual, cultural, and biological methods into a coordinated, season-aware approach. The key is timing – different pests peak at different crop seasons, and effective IPM schedules control interventions to match these periods. For instance, nylon nets and uzi fly monitoring are prioritised from December to March, while ant control and wasp trapping are intensified during the Aherua and Bhodia cycles. Research highlights that preseed crops (Aherua and Jarua) and seed crops (Chotua and Bhodia) experience significantly higher losses compared to commercial crops, making these cycles the priority windows for intensive IPM intervention. Monitoring pest populations at weekly intervals during each crop cycle allows rearers to respond quickly before infestations reach damaging thresholds. The Central Silk Board continues to work with farmers in Assam to develop and refine IPM protocols suited to local agro-climatic conditions.

The way forward for muga pest management 🔗

The outdoor nature of muga rearing makes zero pest pressure an unrealistic goal – the challenge is to keep pest damage below economically significant thresholds using safe, sustainable methods. Future research must focus on environmentally sound pest management strategies that are compatible with the needs and limitations of muga farmers, particularly smallholders whose livelihoods depend on each crop cycle. Improving access to biological control agents like Nesolynx thymus, training rearers in early pest detection, and developing pest-resistant som and soalu plantations are among the most promising directions. Given that muga silk production has declined due to a combination of pest and disease pressure, climate variability, and ecological constraints, strengthening pest management at the farm level is inseparable from the broader goal of sustaining this culturally and economically vital industry.

What do you think? Given that chemical pesticides cannot be used without harming the silkworms themselves, do you think biological control methods like releasing Nesolynx thymus are scalable enough for smallholder muga farmers in Assam? And considering the 100% rate of ant infestation reported across surveyed rearing sites, how much of the current crop loss do you think could realistically be reduced through better farm-level practices alone?

References

1. https://www.eje.cz/artkey/eje-201302-0026_Muga_silkworm_Antheraea_assamensis_Lepidoptera_Saturniidae_-_an_overview_of_distribution_biology_and_breeding.php
2. https://www.walshmedicalmedia.com/open-access/insect-pests-of-muga-silkworm-anthereae-assamensis-lepidoptera-saturniidae.pdf
3. https://jazindia.com/index.php/jaz/article/view/3114
4. https://journalijpss.com/index.php/IJPSS/article/view/4905
5. https://en.wikipedia.org/wiki/Oecophylla_smaragdina
6. https://journaljeai.com/index.php/JEAI/article/view/2355
7. https://www.atshq.org/what-do-silkworms-eat/
8. https://www.researchgate.net/figure/The-muga-silkworm-Antheraea-assamensis-Helfer-undomesticated-silk-producing-insect-in_fig1_313228470
9. https://www.researchgate.net/publication/287071810_Muga_silkworm_antheraea_assamensis_Lepidoptera_Saturniidae_-_An_overview_of_distribution_biology_and_breeding