Key Pests Affecting Tasar Silkworm Host Plants: Identification and Control

Tasar silk – produced by the wild silkworm Antheraea mylitta – depends entirely on healthy foliage from its primary host plants, Terminalia arjuna (Arjun) and Terminalia tomentosa (Asan). These trees are reared outdoors, which means they are constantly exposed to a range of insect pests. When pest pressure goes unchecked, it doesn’t just damage the trees – it directly reduces the quantity and quality of silk produced. Three pests stand out as the most economically significant threats to tasar silkworm host plants: the leaf gall insect (Trioza fletcheri minor), the May-June beetle (Anomala blanchardi), and the stem borer (Sphenoptera konbierensis). Understanding how each one damages the host plant – and how to manage it – is critical for anyone involved in tasar sericulture.

Why pest management in tasar host plants matters 🔗

Unlike mulberry sericulture, where rearing happens in controlled indoor conditions, tasar silkworms are reared outdoors on plantation trees. This exposure to outdoor conditions makes both the silkworms and their food plants vulnerable to a wide complex of insect pests throughout the rearing season. Damage to the host plant reduces the availability of leaves – the silkworm’s only food source – and directly affects cocoon yield, cocoon weight, and silk quality. A decrease in available foliage hurts silkworm development and survival, ultimately leading to fewer and smaller cocoons and lower silk production.

The leaf gall insect: Trioza fletcheri minor 🔗

Trioza fletcheri minor (Hemiptera: Psyllidae) is considered the most important gall-forming pest of tasar host plants. It attacks both T. arjuna and T. tomentosa and is capable of causing 40-50% crop loss during the peak infestation period of August-September.

Identification and damage symptoms 🔗

The insect first appears on fresh tender leaves in March and remains active until mid-November or the onset of leaf fall, with population peaks between July and September. The pest lays eggs on the leaf surface, and once the nymphs hatch, they begin feeding on the leaf tissue. This feeding stimulates the plant to form galls – abnormal tissue growths that develop on both the upper and lower surfaces of leaves. The galls start out greenish but gradually turn brown as they mature. As more nymphal instars develop inside the gall, it enlarges, and the surrounding leaf tissue becomes distorted and unusable.

The damage goes deeper than just the visible deformities. Research published in peer-reviewed sericulture journals found that gall-infested leaves show a significant decrease in photosynthesis rate, transpiration rate, and stomatal conductance compared to healthy leaves. Oxidative stress markers – including lipid peroxidation and hydrogen peroxide production – are also significantly elevated in infested leaves. The result is nutritionally degraded foliage that is unsuitable for silkworm rearing.

Management of the leaf gall insect 🔗

Control is most effective when started early in the season, before population levels build up. A combination of mechanical and chemical methods is recommended:

• Mechanical control: Clip and collect gall-infested leaves – especially tender leaves bearing eggs and mature leaves with developing nymphs – and burn them to prevent the pest from spreading. During the winter months (December-February), old leaves harbouring diapausing nymphs should also be collected and destroyed.
• Chemical control: Systemic insecticides such as Dicrotophos have been studied for their efficacy against T. fletcheri minor. Monocrotophos and similar systemic compounds have also shown effectiveness when applied as foliar sprays during the early infestation period. Spraying should coincide with the appearance of the pest in March-April, before gall formation begins in earnest.
• Biological control: The parasitoid wasp Trechnites aligarhensis has been recorded as a natural enemy of T. fletcheri minor on Terminalia species, offering a potential avenue for future biocontrol strategies.

The May-June beetle: Anomala blanchardi 🔗

The May-June beetle is a well-documented defoliating pest of tasar food plants, with its name derived from its peak activity period. It belongs to the family Scarabaeidae and is one of several coleopteran pests that attack T. arjuna and T. tomentosa plantations during the rearing season.

Identification and damage symptoms 🔗

Adult beetles are active from April through August, with peak infestation recorded in June and August. The adults are the primary damaging stage – they feed directly on the leaf tissue, skeletonizing or completely consuming leaves and causing significant defoliation of host plant canopies. When beetle populations are high, entire branches can be stripped of foliage in a short period.

The grub (larval) stage lives in the soil and feeds on roots and organic matter, which can weaken young plants over time. Repeated defoliation by adults, combined with root damage from grubs, reduces the overall vigour of the plantation and makes trees more susceptible to secondary pest attack.

Management of the May-June beetle 🔗

An integrated approach combining cultural, mechanical, and chemical methods gives the best results:

• Cultural control: Deep ploughing of the soil twice a year – in November-December and again in March-April – exposes grubs and pupae to natural predators and desiccation. This is an important pre-emptive step before the beetle season begins.
• Mechanical control: Collecting and destroying different developmental stages – eggs, grubs, pupae, and adults – during morning and evening hours, twice a week from May to July, is recommended for reducing populations. Adults are easier to collect when temperatures are cooler.
• Soil and foliar applications: Soil application of neem cake (approximately 60 kg per acre in two split doses before the monsoon onset) followed by foliar application of Azadirachtin at 15 ppm has proven effective as a biopesticide approach for managing beetle populations while minimising harm to the silkworms.

The stem borer: Sphenoptera konbierensis 🔗

Sphenoptera konbierensis is a flat-headed borer belonging to the family Buprestidae. It is among the most destructive pests of Terminalia plantations because its damage is internal and often goes undetected until the plant is severely compromised. Flat-headed stem-boring buprestids of this type have been reported to injure 22-40% of Terminalia plantations, depending on field location and management practices.

Identification and damage symptoms 🔗

Adult beetles lay eggs in clusters within bark crevices of young arjuna stems. After hatching, the larvae bore into the stem and begin feeding on the vascular tissue. Young larvae create galleries along the longitudinal axis of the stem, while older larvae tunnel in transverse directions, causing partial or complete girdling of the stem. Externally, infested plants show spiral ridges or cankers on the bark, gum exudation, and cracking. The compacted sawdust-like frass inside the tunnels is another diagnostic sign.

As the larva matures and penetrates deeper into the stem tissue, it significantly impedes the transfer of water and nutrients throughout the plant. This leads to early defoliation, wilting, and – in severe or repeated infestations – plant death. Dead or dying host plants mean no food source for the silkworm, with direct consequences for cocoon production in that season and beyond.

The monoculture nature of tasar plantations and the continuous use of the same trees for silkworm rearing weakens plant vigour over time, making them increasingly attractive to borers. Young and weakened plants are at the highest risk.

Management of the stem borer 🔗

• Timely insecticide application: Insecticidal sprays applied during autumn, targeted at the mid-trunk region of affected 4-8-year-old trees, are recommended as the primary chemical control measure. The autumn season coincides with adult activity and egg-laying, making it the most effective intervention window – before larvae enter the stem.
• Mechanical removal: Injecting kerosene or chlorpyrifos solution directly into the borer holes and sealing them with mud has been used to kill larvae already inside the stem. Cutting and destroying heavily infested plant portions prevents the pest from completing its life cycle and spreading to neighbouring plants.
• Monitoring for early detection: Regularly inspect the bark of young trees for gum exudation, frass deposits, and surface cankers. Early detection – before larvae penetrate deep – significantly improves the chance of saving the plant.

An integrated approach to host plant protection 🔗

None of these pests operates in isolation, and a tasar plantation facing one pest is often more vulnerable to others. The co-occurrence of leaf gall, flat-headed borer, and bark-eating caterpillar on the same plants has been documented, particularly in plantations already weakened by termite damage. This points to the value of a consistent, season-specific pest management calendar rather than reactive spot treatments.

Effective management of tasar host plant pests generally follows this pattern: cultural practices (ploughing, field sanitation) to reduce pest build-up before the season; mechanical methods (collection and destruction of infested plant parts) during active infestation; and timely chemical or biopesticide applications at pest population peaks. The Central Silk Board’s tasar research stations have developed field-level guidance documents that provide region-specific schedules for these interventions, and these should be consulted for location-specific recommendations.

With tasar silk being an important livelihood crop for tribal and forest-dwelling communities across Jharkhand, Chhattisgarh, and Odisha, keeping host plant health at the centre of crop protection planning is not just agronomically important – it is economically essential for the farmers who depend on it.

What do you think? Given that tasar silkworms are reared outdoors with limited ability to control the environment, how feasible is it to implement a strict mechanical pest removal schedule in forest-based plantations? And with increasing concerns about pesticide residues affecting silk quality and ecosystem health, should greater investment go into scaling up biological control options like parasitoid wasps for pests like Trioza fletcheri minor?

References

1. https://cabiagbio.biomedcentral.com/articles/10.1186/s43170-023-00204-z
2. https://www.researchgate.net/publication/274003353_Gall-induced_stress_in_the_leaves_of_Terminalia_arjuna_food_plant_of_tropical_tasar_silkworm_Antheraea_mylitta
3. https://www.wisdomlib.org/science/journal/world-journal-of-pharmaceutical-research/d/doc1369557.html
4. https://www.researchgate.net/figure/Leaf-gall-due-to-infestation-of-T-f-minor-on-T-arjuna-A-Newly-produced-leaf-was-free_fig2_359405730
5. https://www.plantarchives.org/SI%20VSOG/4.pdf
6. https://www.ijcmas.com/abstractview.php?ID=11451&vol=8-1-2019&SNo=67
7. https://link.springer.com/article/10.1186/s43170-023-00204-z
8. https://www.entomoljournal.com/archives/?year=2018&vol=6&issue=6&ArticleId=4612