Dermestid Cocoon Beetle
Dermestes cadaverinus Herbst [and other Dermestes spp.]
📖 Description
Dermestid Cocoon Beetle (Dermestes cadaverinus and related Dermestes species) is a serious stored-product pest of silkworm cocoons across the Indian subcontinent and worldwide. Particularly severe in sericultural regions where cocoons are stored for weeks or months before silk reeling. Particularly common in Karnataka (Ramanagara, Chamarajanagar — India’s largest mulberry silk producer), Andhra Pradesh, Tamil Nadu, West Bengal (Murshidabad, Malda — Murshidabad silk), Assam (Kamrup — muga silk), and Jharkhand (Ranchi, Khunti — tasar silk). India produces over 35,000 tonnes of silk annually. The pest is unusual among stored product pests because (a) both adults and larvae feed on dried animal matter — especially the dried pupa inside silkworm cocoons, but also dried insect specimens, dried fish, leather, wool, furs, and stored grain with animal matter contamination, (b) larvae are hairy and produce allergenic hairs that can cause allergic reactions and dermatitis in silk workers handling infested cocoons, (c) a single female lays 100-200 eggs in crevices of stored cocoons or directly on cocoon surface, with larvae developing over 6-8 weeks and pupating inside the last larval skin, (d) the pest is most damaging to cocoons stored in warm humid conditions (above 25°C and 70% RH) — exactly the conditions common in many Indian sericultural stores, (e) the pest can survive for weeks without food (waiting for new cocoon storage), making eradication from storage rooms difficult, and (f) the pest is a common pest of museums worldwide (damages dried insect specimens). IPM with sealed hermetic storage (most effective), strict hygiene, FIFO stock rotation, freezing of incoming cocoons, aluminium phosphide fumigation for long-term storage, diatomaceous earth, monitoring with pheromone traps, and cool dry storage conditions provides effective control. The pest is a particular concern for Indian sericulture because (i) India is the world’s second largest silk producer, (ii) cocoons are typically stored for weeks or months before silk reeling (allowing beetle population buildup), (iii) much Indian sericulture uses traditional storage (open baskets or jute bags — not hermetic) which favours beetle infestation, (iv) India’s warm humid climate favours beetle development year-round in many regions, (v) damaged cocoons cannot be reeled into continuous silk filament and must be downgraded to spun silk at 50% price reduction — directly impacting farmer income, and (vi) many Indian sericultural storage facilities lack proper hygiene and pest management.
⚠️ Symptoms to watch for
- Damage to stored silkworm cocoons: beetles and larvae bore into cocoons and feed on the dried pupa inside, leaving characteristic round exit holes in cocoons, frass accumulation inside cocoons, cocoons become valueless for silk reeling (hole prevents continuous filament reeling), contaminated cocoons with beetle hairs and frass (causes allergic reactions in silk workers), damaged grain storage with animal matter contamination. Economic loss: 5-15% of stored cocoons in neglected storage, up to 40% in severely infested storage; quality downgrade of damaged cocoons from reelable to spun-silk (50% price reduction).
🩹 Treatment
- Inspect stored cocoons every 7-10 days and remove infested cocoons, freeze infested cocoons at -7°C for 4.5 hours (kills all stages), fumigate stored cocoons with aluminium phosphide (Phostoxin) tablets @ 1 tablet per tonne cocoons in sealed stacks (effective — use only by trained operators), fumigate with methyl bromide (largely discontinued — ozone-depleting), use PDB (para-dichlorobenzene) crystals in sealed storage stacks (less effective on Dermestes than on wax moth), keep storage rooms clean and dry, store cocoons in sealed plastic-lined containers, practice first-in-first-out (FIFO) stock rotation.
🌿 Organic treatments
- Freeze infested cocoons at -7°C for 4.5 hours (kills all stages), expose cocoons to bright sunlight in sealed clear plastic bags (heat kills larvae), apply diatomaceous earth (DE) @ 1 kg per tonne cocoons (abrasive to insect cuticle — kills beetles by desiccation, safe to mammals), use neem oil 0.5% spray on storage containers (repels adults), apply Beauveria bassiana spores on storage room floor (entomopathogenic fungus — kills larvae), use essential oil blends (clove, peppermint, eucalyptus) in storage rooms (repels adults), practice strict hygiene (clean storage rooms between batches, remove and burn infested stock), use hermetic storage (sealed plastic-lined bags with low oxygen — kills all stages within 2 weeks).
🧪 Chemical treatments
- Aluminium phosphide (Phostoxin) tablets @ 1 tablet per tonne cocoons in sealed stacks (most effective — use only by trained operators, lethal to humans if mishandled), PDB (para-dichlorobenzene) crystals @ 50 g per cubic metre of storage space (effective against adults and larvae), deltamethrin 0.05% spray on storage room walls and floor (kills adults — do not apply to cocoons), malathion 0.5% dust on storage room floor (limited use — resistance common). NEVER apply insecticides directly to cocoons destined for silk reeling — residues contaminate silk.
🛡️ Prevention
- Store cocoons in sealed plastic-lined containers or hermetic storage bags (excludes beetles), practice first-in-first-out (FIFO) stock rotation (do not store old cocoons with new), keep storage rooms clean and dry (beetles thrive in humid dirty storage), inspect incoming cocoons for beetle damage before storing, freeze all incoming cocoons at -7°C for 4.5 hours before storage (kills any hitchhiking beetles), fumigate empty storage rooms with aluminium phosphide before filling, install insect-proof mesh on storage room windows and doors, store cocoons in cool dry conditions (below 25°C and 60% RH — slows beetle development), use diatomaceous earth (DE) in storage containers (kills beetles by desiccation), monitor with pheromone traps (Dermestes pheromone available commercially — early warning of infestation), do not store cocoons near grain stores or dried fish (cross-infestation risk), burn infested stock immediately, practice strict hygiene between batches.
🪴 Affected plants
- Stored silkworm cocoons (Bombyx mori — mulberry; Antheraea assamensis — muga; Antheraea mylitta — tasar; Philosamia ricini — eri); dried insect specimens in museums; stored grain with animal matter; dried fish; leather; wool; furs. Not a plant pest — a stored product pest of dried animal matter, especially silkworm cocoons in sericulture.
🦋 Natural predators
- Spiders (capture adults in storage rooms), predatory bugs (Xylocoris spp. — limited efficacy), parasitic wasps (Bracon hebetor — limited efficacy on Dermestes larvae), mites (Pyemotes tritici — parasitises larvae, limited use). No commercial biological control agents are widely used in sericultural storage.
🌱 Host plants
- Stored silkworm cocoons (Bombyx mori, Antheraea assamensis, Antheraea mylitta, Philosamia ricini); dried insect specimens; stored grain with animal matter; dried fish; leather; wool; furs. Not a plant pest.
🔄 Lifecycle
- Adult female lays 100-200 eggs in crevices of stored cocoons or directly on cocoon surface.
- Egg incubation 4-6 days.
- Larva passes through 6-8 instars over 35-60 days (depending on temperature and food quality); larvae bore into cocoons and feed on dried pupae.
- Mature larva pupates inside the last larval skin in a protected crevice.
- Pupal stage 7-14 days.
- Adult lifespan 30-60 days (continues to feed and lay eggs).
- Total life cycle 6-10 weeks at 25-30°C; 4-6 overlapping generations per year in tropical India.
- Adults can survive 4-6 weeks without food; larvae can survive 8-12 weeks without food.
📅 Season
- Year-round in tropical India; peaks Jun-Nov (warm humid monsoon and post-monsoon conditions most favourable for beetle reproduction, and cocoon storage is most common during this period after the main rearing season)
🔎 Appearance
- Adult is a medium-sized, oval, dark brown to black beetle (family Dermestidae) with distinctive white and dark patterned elytra; underside covered with fine white hairs; clubbed antennae fit into a groove on the underside.
- Larvae are hairy, brown, segmented grubs with two upward-curving spines (urogomphi) at the tail end — distinct from other stored product beetle larvae by the hairy body and urogomphi.
- Pupae are inside the last larval skin.
- Adults and larvae feed on dried silkworm cocoons, dried insect specimens, stored grain, and other dried animal products.
💥 Damage level
- Moderate
🔁 Reproduction rate
- Fast
🗺️ Geographic regions
- Indian Subcontinent
- South Asia
- Southeast Asia
- Cosmopolitan Worldwide
Have an Insect to Identify?
Upload or take a photo of an insect on your plant and our AI will identify it and recommend treatments.
📷 Diagnose from Image