Mesta Shoot Webber
Crocidosema sp.
📖 Description
The Mesta Shoot Webber is a tortricid moth pest of mesta (Hibiscus cannabinus, also known as kenaf) — one of India’s most important bast-fibre crops after cotton and jute. Mesta is grown on over 80,000 hectares in India, primarily in Andhra Pradesh, Odisha, West Bengal, Bihar, and Assam, and is valued for its drought tolerance and ability to produce fibre on marginal soils where jute cannot be grown. The shoot webber is one of the most consistent lepidopteran pests of the crop, though it has historically received less research attention than the more visible mesta hairy caterpillar (Spilosoma obliqua). The female moth lays eggs on the tender apical leaves; the emerging larva webs the leaves together with silk and feeds inside the shelter, protected from natural enemies and insecticide sprays. The webbing behaviour makes the pest disproportionately difficult to control with contact insecticides — high-volume sprays with a sticker are needed to penetrate the silk. Damage is most severe when infestation occurs during the first 60 days after sowing, when the main stem is elongating rapidly and apical meristem damage stunts the entire plant. IPM packages developed by CRIJAF (Central Research Institute for Jute and Allied Fibres) Barrackpore emphasise weekly shoot pruning, Btk applications, and balanced nutrition as the core management tactics. The pest has 5–6 overlapping generations per year in India’s mesta belt, with peak activity during the warm humid monsoon and post-monsoon periods when the crop is at peak vegetative growth.
⚠️ Symptoms to watch for
- Webbed apical leaves with frass and excreta inside the web
- chewed leaf margins around the web
- wilting and drying of the apical shoot beyond the webbing point
- stunting of the main stem and reduced fibre yield.
- In mesta crops in Andhra Pradesh (Srikakulam, Vizianagaram, Visakhapatnam), Odisha (Koraput, Rayagada, Gajapati), West Bengal, and Bihar, heavy infestation can reduce fibre yield by 15–25 % through stunting of the main stem.
🩹 Treatment
- Cultural: hand-pick and destroy webbed shoots in small fields
- prune off infested shoot tips and burn them.
- Mechanical: install light traps at 2/ha to monitor adult activity.
- Biological: spray Bacillus thuringiensis var. kurstaki (Btk) at 1 g/L on tender shoot growth at 15-day intervals
- release Trichogramma chilonis at 50,000/ha for egg parasitism.
- Chemical: spray quinalphos 25 EC @ 1.5 ml/L or chlorpyrifos 20 EC @ 2 ml/L directed at the apical shoot, ensuring the spray penetrates the webbing.
🌿 Organic treatments
- Spray neem oil (Azadirachta indica) at 3 % emulsion on tender shoot growth at 15-day intervals
- apply Beauveria bassiana at 5 g/L on the webbed shoots
- install light traps at 2/ha for adult monitoring
- hand-pick and destroy webbed shoots weekly.
🧪 Chemical treatments
- Quinalphos 25 EC @ 1.5 ml/L, Chlorpyrifos 20 EC @ 2 ml/L, Lambda-cyhalothrin 5 EC @ 0.5 ml/L, Emamectin benzoate 5 SG @ 0.4 g/L.
- Use a high-volume spray with a sticker to penetrate the silk webbing.
- Pre-harvest interval 21 days
- mesta is harvested 120–150 days after sowing so residues are typically below MRL by harvest.
🛡️ Prevention
- Prune and destroy infested shoots weekly during the period of tender growth (July–October)
- avoid excessive nitrogen fertilisation that promotes continuous tender flushes
- adopt early sowing (May–June) so the crop passes the vulnerable seedling stage before peak adult activity
- remove wild Malvaceae hosts around field margins
- install light traps at 2/ha to monitor adult emergence and time sprays precisely.
🪴 Affected plants
- Mesta (Hibiscus cannabinus, Hibiscus sabdariffa var. altissima) — primary host
- also reported on roselle (Hibiscus sabdariffa) and occasionally on okra (Abelmoschus esculentus) and other Malvaceae.
🦋 Natural predators
- Trichogramma chilonis (egg parasitoid — 20–30 % field parasitism in unsprayed fields)
- Apanteles spp. (larval braconid parasitoids)
- predatory pentatomid bugs (Eocanthecona furcellata)
- lacewing larvae (Chrysoperla zastrowi)
- spiders (Thomisidae, Salticidae)
- and predatory ants.
🌱 Host plants
- Hibiscus cannabinus (mesta/kenaf — primary)
- Hibiscus sabdariffa var. altissima (roselle fibre type)
- Hibiscus sabdariffa (roselle — minor)
- Abelmoschus esculentus (okra — rare).
🔄 Lifecycle
- Adult female lays 80–200 eggs singly or in small clusters on tender apical leaves.
- Egg stage 4–6 days.
- Larva passes through five instars over 15–22 days, webbing leaves and feeding inside.
- Pupation occurs inside the webbed leaves or in soil; pupal stage 8–12 days.
- Adult longevity 7–14 days.
- Total lifecycle 30–45 days.
- Five to six overlapping generations per year.
📅 Season
- Active June–November across the Indian mesta belt; peak infestation August–October during the monsoon and post-monsoon periods when the crop is at peak vegetative growth.
- Population crashes during the cool dry winter.
🔎 Appearance
- Adult is a small brownish-grey tortricid moth with a characteristic dark oblique band across each forewing and a paler patch near the wing tip; at rest, the wings are held roof-like over the body giving a bell-shaped outline.
- Larva is a small greenish-brown caterpillar with a dark head capsule and sparse pale setae; the larva webs together the apical leaves of the mesta shoot with silk, forming a shelter inside which it feeds.
- Pupa is dark brown, 6–8 mm long, found inside the webbed leaves.
💥 Damage level
- Moderate
🔁 Reproduction rate
- Medium
🗺️ Geographic regions
- Indian Subcontinent (Andhra Pradesh, Odisha, West Bengal, Bihar, Assam)
- South Asia
- parts of Southeast Asia.
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