Deodar Weevil
Dyscerus clathratus
📖 Description
Dyscerus clathratus is the most important stem-boring pest of deodar cedar in the Himalayan forestry belt. Deodar cedar is India’s most valuable timber species — Indian deodar forests cover approximately 207,000 ha in Himachal Pradesh, Uttarakhand, and J&K, producing timber worth ₹500–800 crore annually. The species is also culturally significant — deodar wood is used in temple construction throughout the Himalayan region, including the famous Kedarnath and Tungnath temples. The weevil is a particular problem in young plantations (5–15 years old) established after logging of mature deodar forests; monoculture plantations on degraded sites are most susceptible. Outbreaks were reported from the Kullu and Shimla forest divisions of Himachal Pradesh in 2018–2020, with 35 % mortality in some 8-year-old plantations. The weevil has a 2-year lifecycle — adults emerge in April–May, feed on young shoots, and oviposit in bark crevices; larvae feed under the bark for 18–20 months before pupating. Semivoltine.
⚠️ Symptoms to watch for
- Adults feed on the bark of young shoots causing dieback; larvae bore under the bark of the main stem and large branches, producing characteristic frass-filled galleries that girdle and kill young trees; entry holes (3–5 mm diameter) with frass accumulations are visible at the base of wilted shoots; severely attacked young plantations (5–15 years old) can suffer 30–50 % mortality; surviving trees show reduced growth and become susceptible to secondary fungal infections.
🩹 Treatment
- Prune and burn all infested shoots and branches 10 cm below the lowest borehole — do this weekly during the active season (April–October). Spray lambda-cyhalothrin 5 EC at 0.5 ml/L or chlorpyriphos 20 EC at 2 ml/L on the stem and main branches of young trees at 30-day intervals during the active season. Apply carbofuran 3 G at 20 g per tree around the root zone of young trees in April-May.
🌿 Organic treatments
- Prune and burn infested shoots weekly. Apply Beauveria bassiana at 5 g/L as a stem spray at 30-day intervals. Apply Metarhizium anisopliae at 5 g/L as a soil drench around the root zone. Use neem oil (1 % Azadirachtin) at 5 ml/L as a stem spray. Release predatory birds (woodpeckers) by maintaining snags and dead wood in plantations — woodpeckers can remove 40–60 % of larvae from infested trees.
🧪 Chemical treatments
- Lambda-cyhalothrin 5 EC (0.5 ml/L), chlorpyriphos 20 EC (2 ml/L), or carbofuran 3 G (20 g/tree as soil application). Apply as stem spray or soil drench at 30-day intervals during the active season (April–October).
🛡️ Prevention
- Plant deodar at recommended spacing (3 m × 3 m for timber plantations) to ensure vigorous growth — stressed trees are more susceptible. Avoid planting deodar on sites with poor drainage. Maintain species diversity — mixed conifer-broadleaf plantations are less susceptible than monocultures. Inspect plantations monthly during the active season and remove infested trees promptly. Use nursery stock from certified disease-free sources.
🪴 Affected plants
- Deodar cedar (Cedrus deodara) is the primary host; also recorded on Himalayan blue pine (Pinus wallichiana), chir pine (Pinus roxburghii), spruce (Picea smithiana), fir (Abies pindrow), and occasionally Himalayan yew (Taxus wallichiana) in mixed conifer forests.
🦋 Natural predators
- Woodpeckers (Dendrocopos auriceps — brown-fronted woodpecker, Picus canus — grey-headed woodpecker) remove 40–60 % of larvae from infested trees in natural forests. Parasitoid wasps (Eurytoma spp., Eupelmus spp.) and predatory beetles (Cleridae) attack larvae under bark. Entomopathogenic fungi (Beauveria bassiana, Metarhizium anisopliae) provide natural regulation in moist forests.
🌱 Host plants
- Cedrus deodara (deodar cedar — primary host), Pinus wallichiana (Himalayan blue pine), Pinus roxburghii (chir pine), Picea smithiana (spruce), Abies pindrow (fir), Taxus wallichiana (Himalayan yew).
🔄 Lifecycle
- Egg (10–15 days, laid in bark crevices) → Larva (18–20 months, under bark, girdling) → Pupa (15–25 days, in bark chamber) → Adult (60–90 days, April–June emergence).
- Semivoltine — one generation every 2 years.
📅 Season
- Adult emergence and flight: April–June (post-winter).
- Oviposition: May–July.
- Larval feeding: continuous for 18–20 months.
- Pupation: March–April of the second year.
🔎 Appearance
- Adult is a large, robust, dark brown-black weevil with a thick, slightly curved rostrum (snout) about half the body length; the elytra are covered with fine greyish scales giving a mottled appearance and have longitudinal rows of deep punctures; femora are toothed and reddish-brown.
- Larvae are creamy-white, legless grubs with a brown head capsule, found feeding under bark; mature larvae reach 15 mm.
💥 Damage level
- Severe
🔁 Reproduction rate
- Slow
🗺️ Geographic regions
- Himalayan conifer belt of India (Himachal Pradesh — Kullu
- Shimla
- Mandi
- Chamba; Uttarakhand — Garhwal
- Kumaon; J&K — Kashmir
- Jammu). Also reported from Pakistan (Azad Kashmir)
- Nepal
- and Afghanistan.
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