Key Pests Affecting Tasar Silkworms and Their Management

Tasar silk – the coarse, golden-brown wild silk prized for its natural texture – is produced by Antheraea mylitta, a forest silkworm reared outdoors on trees like Terminalia arjuna, Terminalia tomentosa, and Shorea robusta. Unlike mulberry silkworm rearing, which happens in controlled indoor environments, tasar silkworm rearing takes place in open forest settings – and that exposure comes at a cost. Research has shown that pests and predators in these outdoor settings are responsible for more than 40% of losses to the tasar silk industry, directly and indirectly. Among the many threats tasar silkworms face, a specific group of insect pests – parasitoid flies and predatory insects – consistently cause the most damage. Understanding these pests and the methods used to manage them is essential for any serious sericulturist.

The Uzi fly: the most damaging parasitoid of tasar silkworms 🔗

Of all the insect pests that attack tasar silkworms, the Uzi fly (Blepharipa zebina Walker, family Tachinidae) is the most destructive. According to published research, this fly alone can be responsible for up to 40% crop loss in tasar silk production – making it the single biggest biological threat to the industry.

How the Uzi fly attacks 🔗

Blepharipa zebina is a larval endoparasitoid, meaning its young develop inside the living body of the silkworm larva. The female fly deposits eggs directly onto the outer skin (integument) of the larval host, particularly on the dorsal and dorso-lateral sides. Once the eggs hatch, first-instar maggots bore through the silkworm’s cuticle, leaving a characteristic black scar on entry. Inside the larval body, the maggots pass through three instars over 20-25 days, feeding on the fat tissues and internal organs of the host. Mature maggots eventually exit through the larva or pupa, making a small pore at the distal end of the cocoon before pupating in the rearing field or grainage.

The physiological damage is severe. Studies on host-parasitoid interaction have found that B. zebina parasitization causes 100% mortality of A. mylitta during either the larval or pre-pupal stage, with 76-99% of maggots successfully emerging from the host. Even lower-level infestations cause significant harm: cocoon shell weight decreases by 27-63.5% in parasitized groups, and larvae infested with higher maggot loads completely fail to spin cocoons. The fly is known to deposit up to 50 eggs on a single host in natural conditions, compounding the damage dramatically.

Peak infestation period 🔗

Both the Uzi fly and the Ichneumon fly (discussed below) are most active between September and January. Data from the Central Silk Board of India indicates that peak infestation of both parasitoids is concentrated in December and January, coinciding with key rearing seasons. This seasonality helps farmers time their management interventions more precisely.

IPM measures for Uzi fly control 🔗

An integrated pest management (IPM) approach is recommended for B. zebina, combining mechanical, cultural, chemical, and biological strategies:

• Mechanical removal: Uzi fly-infested and dead silkworm larvae should be collected and destroyed promptly. Maggots and pupae found in rearing fields or grainage houses must also be collected and disposed of.
• Early harvest: Flimsy and fly-infested cocoons should be harvested early and stifled or sun-dried to prevent adult fly emergence.
• Sticky traps: Lassa-adhesive sticky traps are used to catch and kill adult Uzi flies in and around rearing areas.
• Chemical control: A 2% bleaching powder solution acts as an ovicide and should be sprayed on the silkworm body to kill Uzi fly eggs glued to the integument. This spray schedule is typically applied once on the 3rd day of the 4th instar, and on the 3rd, 5th, and 7th days of the 5th instar (with an additional spray on the 9th day if larval duration is prolonged).
• Biological control: Parasitoids of the Uzi fly itself – such as Trichomalopsis apanteloctena and Pediobius spp. (Hymenoptera) – have been studied and deployed as biocontrol agents. Research published in Integrated Pest Management Reviews highlights that fitting fly-proof wire mesh screens to windows, ventilators, and doors, and securing nylon nets to individual rearing trays, are among the most eco-friendly and economically viable cultural exclusion methods available.

The Ichneumon fly: a pupal parasitoid 🔗

While the Uzi fly targets larvae, the Ichneumon fly – more accurately the Yellow fly (Xanthopimpla pedator Fabricius, family Ichneumonidae) – attacks at the pupal stage. It is a major pupal endoparasitoid of A. mylitta and a serious threat to seed production and next-generation silkworm availability.

How X. pedator parasitizes the pupa 🔗

Research on the oviposition and feeding behavior of X. pedator describes how gravid females locate the immobile pupal host using vibrational sounding – essentially a form of echolocation on solid substrate – to detect the pupa within the cocoon. The female then pierces the cocoon wall using its long, specialized ovipositor and deposits a single egg into the prepupa or mature pupa of A. mylitta. A single egg develops into one offspring per host. The emerging larva proceeds to consume the entire internal body content of the pupa over a development period of 20-22 days, resulting in a dead or seedless cocoon. The adult parasitoid eventually exits by rupturing the peduncle end of the cocoon – a distinguishing feature that helps identify parasitized cocoons in the field, since the exit hole of the Ichneumon fly appears at the peduncle side, while the Uzi fly’s exit hole appears on the opposite end.

Research has also found that X. pedator shows a preference for male cocoons of A. mylitta – a study from Uttarakhand reported that 85.59% of infested pupae were male – though the precise reasons for this sex-specific parasitism remain an area of ongoing investigation. Pupal mortality from this pest is significantly higher during the second rearing season than the first.

Management of the Ichneumon fly 🔗

The management approach for X. pedator is primarily mechanical and cultural, as chemical control is not practical without harming the silkworms themselves:

• Nylon net protection: Rearing tasar silkworms under nylon net enclosures (mesh size 2 mm), especially during the late larval stages through cocoon formation, physically excludes the Yellow fly from accessing the pupae.
• Sticky traps: Adult Yellow flies (both males and females) can be trapped manually using gummy sticks during the active rearing period.
• Destruction of infested cocoons: Cocoons containing developing embryos of the parasitoid should be identified and destroyed. Adult Yellow flies that emerge inside grainage houses should be killed by piercing the anterior end of preserved cocoons.
• Sorting and stifling: Thorough sorting of infested cocoons immediately after harvest, followed by stifling, helps contain the spread of the pest to subsequent rearing cycles.

Predatory insects: stink bugs, praying mantis, and wasps 🔗

Beyond parasitoid flies, tasar silkworms face direct predation from several insect species that physically attack and consume the larvae. Because tasar rearing is conducted outdoors on forest trees, physical exclusion is not always feasible for all predators, and identification and timely intervention become critical.

Stink bug (Eocanthecona furcellata) 🔗

The stink bug Eocanthecona furcellata (family Pentatomidae) is a significant predatory pest in tasar sericulture. It is an active predator that attacks both silkworm larvae and cocoons. Research documenting parasites and predators of A. mylitta in central India identifies it as a major larval predator, noting that infested larvae show characteristic damage from the bug’s piercing mouthparts. Control measures include manual collection and destruction of the bugs and their egg masses from the rearing field, and the use of nylon nets to physically limit their access to early-instar larvae during the chawki (young larva) rearing stage.

Praying mantis (Hierodula bipapilla) 🔗

The praying mantis Hierodula bipapilla is active across all three tasar rearing seasons and preys on silkworm larvae at multiple developmental stages. It is identified by its raptorial forelegs – modified for seizing prey – and its triangular head on an elongated thorax. Field studies in central India have observed that both nymphs and adults of H. bipapilla preferably feed on early-instar larvae of A. mylitta, though third and fourth instar larvae and even fifth instar larvae are sometimes targeted. The female deposits her egg mass (called an ootheca) directly on the host plants, meaning entire generations of this predator are effectively stationed in the rearing area. Control involves mechanical removal of oothecae from host plants before they hatch, and manually removing individual mantis nymphs and adults from the rearing trees.

Wasps (Vespa orientalis and Polistes spp.) 🔗

Wasps are among the most aggressive and mobile predators of tasar silkworms. Vespa orientalis (the common wasp) and several Polistes species – particularly P. olivaceus, P. stigma, and P. strigosus – are recognized as serious threats. Reports from major tasar-growing regions in Jharkhand, West Bengal, and Odisha highlight that predatory wasps have become an increasingly significant concern in recent years. Wasps paralyze early-instar silkworm larvae by stinging them, then carry the paralyzed larvae back to their nests as food. Polistes species are social insects that construct paper nests from wood fibers near the rearing area, and their colonies include workers, drones, and egg-laying queens – making them persistent, colony-level threats. They are also attracted to plants that emit frass odors or show herbivore-induced damage, which effectively draws them toward actively feeding silkworm larvae.

Management of wasps involves locating and destroying nests near rearing areas, using protective nylon nets during vulnerable larval stages, and manually removing individual wasps during rearing operations.

General protective measures and integrated management 🔗

Across all these pests, a few general practices form the backbone of effective tasar pest management:

• Nylon net enclosures (mesh size 2 mm) are the most universally recommended physical barrier for protecting silkworms from both parasitoid flies and predatory insects, particularly during the vulnerable chawki rearing phase and the late larval stage through cocoon formation.
• Regular field monitoring during peak pest periods (September-January) allows early detection and timely intervention before infestations become severe.
• Hygienic rearing practices – including prompt removal of dead or diseased larvae, disinfection of rearing areas, and proper disposal of infested cocoons – reduce pest populations in subsequent rearing cycles.
• Biological control using naturally occurring parasitoids of the Uzi fly (such as Trichomalopsis apanteloctena) offers a sustainable supplement to chemical approaches, particularly given that direct chemical pesticide application risks harming the silkworms themselves.

The outdoor nature of tasar silkworm rearing will always leave these insects exposed to a complex web of natural enemies. The key is not to eliminate that exposure entirely – which is largely impossible – but to reduce pest pressure at the most critical points in the silkworm’s life cycle through a combination of physical exclusion, timely mechanical removal, targeted chemical treatment, and biological control.

What do you think? Given that tasar silkworms must be reared outdoors and cannot be fully shielded from natural enemies, which pest management strategy – physical exclusion, biological control, or chemical treatment – do you think should be prioritized for maximum crop protection? And with peak Uzi fly and Ichneumon fly infestations concentrated in December and January, how should rearing schedules be adjusted to reduce the risk of crop loss during these high-pressure months?

References

1. https://link.springer.com/chapter/10.1007/978-1-4615-1377-3_22
2. https://www.sciencedirect.com/science/article/abs/pii/S0022201104001612
3. https://silks.csb.gov.in/mahoba/diseases-and-pests-of-silkworms/
4. https://link.springer.com/article/10.1023/A:1012982030848
5. https://www.sciencedirect.com/science/article/abs/pii/S1226861516302321
6. https://koreascience.or.kr/article/JAKO201304164263243.page
7. https://www.researchgate.net/publication/310773553_Parasites-PredatorsTheir_Occurrence_and_Invasive_Impact_on_the_Tropical_Tasar_Silkworm_Antheraea_mylitta_Drury_in_the_Zone_of_Central_India
8. https://www.researchgate.net/publication/346785204_AVIAN_PESTS_OF_TASAR_SILKWORM_ANTHERAEA_MYLITTA_DRURY_SATURNIIDAE_LEPIDOPTERA_FROM_INDIA