Groundnut Seed Beetle (Groundnut Bruchid)
Caryedon serratus
📖 Description
Caryedon serratus — the Groundnut Seed Beetle or Groundnut Bruchid — is one of the most damaging stored-product insect pests of groundnut in India, with economic significance centred on the groundnut-producing belts of Gujarat (Junagadh, Rajkot, Amreli, Jamnagar — India’s largest groundnut-growing state, producing ~40% of national output), Andhra Pradesh (Anantapur, Kurnool, Chittoor), Tamil Nadu (Thoothukudi, Virudhunagar, Ramanathapuram), Karnataka (Raichur, Koppal, Ballari), Maharashtra (Jalgaon, Dhule, Nandurbar), Telangana (Mahbubnagar, Nagarkurnool), and Rajasthan (Bikaner, Nagaur). India is the world’s second-largest groundnut producer (~10 million tonnes from ~5 million ha), with groundnut being a major oilseed crop (~50% of Indian groundnut is crushed for edible oil, the rest consumed as confectionery). The pest is native to Africa but has spread worldwide through the international groundnut trade — it was first reported in India in the 1950s and has since become established as a major stored-groundnut pest in all Indian groundnut-growing states. The pest’s biology makes it particularly damaging: (1) adults do NOT feed — all damage is caused by larvae developing inside groundnut pods and seeds; (2) females lay 50–150 eggs on the surface of groundnut pods — high reproductive potential; (3) larvae bore THROUGH the hard pod shell to reach the seeds inside — protected from contact insecticides; (4) the pest attacks maturing pods in the FIELD, allowing re-infestation of newly harvested crop; (5) tamarind (Tamarindus indica) serves as an alternative wild host — maintaining pest populations between groundnut crops; (6) the pest destroys groundnut SEED viability — affected seeds have zero germination, requiring growers to purchase fresh seed; and (7) high insecticide resistance — the pest has documented resistance to organophosphates and pyrethroids in some Indian populations. The economic impact is severe: heavy infestations can destroy 40–70% of stored groundnut seeds within 4–6 months of storage. With groundnut valued at ₹50–80 per kg (pod) and groundnut seed valued at ₹80–120 per kg, even moderate infestations cause disproportionate economic loss — for a typical Gujarat groundnut grower storing 5 tonnes of groundnut for 6 months (waiting for higher off-season prices), a severe C. serratus infestation can wipe out ₹50,000–100,000 of income. Management is best achieved through IPM combining sun-drying to <8% moisture, hermetic storage bags (PICS bags), godown hygiene, threshold-based fumigation (aluminium phosphide), diatomaceous earth application, regular inspection, FIFO stock rotation, sealed storage containers, shelling before storage (eliminates protected oviposition sites), limited-duration storage, prompt harvest, and destruction of tamarind alternative hosts near godowns. The Indian Institute of Oilseeds Research (ICAR-IIOR, Hyderabad) and the National Research Centre for Groundnut (ICAR-NRCG, Junagadh, now ICAR-Directorate of Groundnut Research) are the primary research institutions for groundnut IPM in India. The pest's relationship with tamarind (Tamarindus indica) is ecologically interesting — tamarind is the original wild host of C. serratus in Africa (where the pest evolved), and the pest has maintained its preference for tamarind even after spreading to groundnut-growing regions worldwide. In India, tamarind trees growing near groundnut godowns serve as persistent reservoirs of C. serratus infestation — destroying these trees is one of the most effective prevention measures, though it conflicts with tamarind's value as a fruit and shade tree.
⚠️ Symptoms to watch for
- Adults emerge from stored groundnut pods, mate, and females lay 50–150 eggs on the surface of groundnut pods. Larvae hatch in 5–7 days and bore THROUGH the pod shell INTO the groundnut seeds — creating a characteristic entry hole surrounded by frass. Larvae feed inside the seed for 25–35 days, consuming the cotyledons and reducing the seed to a hollow shell filled with frass. Adult emergence leaves a characteristic large circular exit hole (3–5 mm) on the pod shell. Heavy infestations can destroy 40–70% of stored groundnut seeds within 4–6 months of storage. The pest is especially damaging to groundnut meant for seed — affected seeds have zero germination, requiring growers to purchase fresh seed. The pest also attacks groundnut in the field before harvest, allowing re-infestation of newly harvested crop. Groundnut oil quality is also affected — infested seeds have higher free fatty acid content, reducing oil shelf life.
🩹 Treatment
- Fumigate stored groundnut pods with aluminium phosphide (Celphos) at 1 tablet (3 g) per tonne for 72 hours in a sealed godown — kills all stages including eggs inside pods. Apply malathion 5% DP at 250 g per 100 kg of pods — contact insecticide dust. Apply deltamethrin 2.8 EC at 0.5 ml/L as a surface spray on godown walls. Apply spinosad 240 SC at 0.5 ml/L — reduced-risk insecticide. Apply diatomaceous earth at 1 kg per tonne of pods — physical desiccant. Sun-dry groundnut pods to moisture content <8% before storage. Use hermetic storage bags (PICS bags) — oxygen depletion kills all stages.
🌿 Organic treatments
- Hermetic storage bags (PICS bags) — double-layer plastic bags; oxygen depletion kills all stages within 2–4 weeks; OMRI-listed. Diatomaceous earth (SilicoSec) — 1 kg per tonne of pods; physical desiccant; OMRI-listed. Spinosad 240 SC (Natroba) — 0.5 ml/L; OMRI-listed. Neem seed kernel extract (NSKE) 5% — azadirachtin disrupts larval development. Sun-drying — dry pods to <8% moisture for 4–6 hours; kills eggs and larvae. Cold storage at 5–10 °C — kills all stages. Modified atmosphere storage — flush godown with CO2 or N2. Vegetable oil treatment — coat pods with 5–10 ml of edible oil per kg; suffocates eggs and larvae. Sand or ash admixture — mix equal volume of clean dry sand or wood ash; prevents adult oviposition. Store groundnut as SHELLED seeds rather than pods (shelling eliminates protected oviposition sites on pods).
🧪 Chemical treatments
- Aluminium phosphide (Celphos) — 1 tablet (3 g) per tonne; fumigant; kills all stages; 72-hour exposure in sealed godown; RESTRICTED-USE in India. Malathion 5% DP — 250 g per 100 kg of pods; contact organophosphate. Deltamethrin 2.8 EC (Decis) — 0.5 ml/L; surface spray on godown walls. Spinosad 240 SC (Natroba) — 0.5 ml/L; reduced-risk insecticide. Pirimiphos-methyl 50 EC (Actellic) — 8 ml/L; surface spray on godown walls. Cypermethrin 0.5% DP — 100 g per 100 kg of pods; pyrethroid dust. Avoid applying insecticides directly to groundnut meant for human consumption or oil extraction. Rotate IRAC groups to prevent resistance.
🛡️ Prevention
- Sun-dry groundnut pods to moisture content <8% before storage — low moisture inhibits pest development. Inspect all incoming groundnut lots for adult emergence holes — reject infested lots. Use hermetic storage bags (PICS bags) — oxygen-depleted environment kills all stages. Maintain godown hygiene — sweep and clean godowns before loading new crop. Fumigate empty godowns with aluminium phosphide before loading new crop. Apply diatomaceous earth or malathion dust at the time of storage. Inspect stored groundnut monthly; remove infested lots immediately. Store groundnut as SHELLED seeds rather than pods (shelling eliminates protected oviposition sites on pods). Store in sealed plastic or metal containers. Maintain first-in-first-out (FIFO) stock rotation. Avoid storing groundnut for more than 6 months. Use cold storage for high-value groundnut seed. Maintain 100 m isolation between groundnut storage godowns and processing units. Apply threshold-based fumigation (1 adult per kg of pods). Harvest groundnut promptly at maturity — late-harvested groundnut is more likely to be field-infested. Destroy tamarind trees (alternative wild host) near groundnut godowns — these maintain pest populations between groundnut crops.
🪴 Affected plants
- Groundnut (Arachis hypogaea — primary host). Also on tamarind (Tamarindus indica — alternative wild host, gives the species its alternative name 'Tamarind Beetle') and other Caesalpinioideae legumes — Bauhinia species, Cassia species, Caesalpinia species. In India, the pest is most damaging in groundnut-producing belts of Gujarat (Junagadh, Rajkot, Amreli, Jamnagar — India's largest groundnut-growing state), Andhra Pradesh (Anantapur, Kurnool, Chittoor), Tamil Nadu (Thoothukudi, Virudhunagar, Ramanathapuram), Karnataka (Raichur, Koppal, Ballari), Maharashtra (Jalgaon, Dhule, Nandurbar), Telangana (Mahbubnagar, Nagarkurnool), and Rajasthan (Bikaner, Nagaur).
🦋 Natural predators
- Anisopteromalus calandrae (pteromalid pupal parasitoid — also attacks stored-product pests; under evaluation by NBAIR Bangalore). Dinarmus basalis (pteromalid larval-pupal parasitoid — under evaluation). Lariophagus distinguendus (pteromalid larval parasitoid — attacks larvae inside groundnut pods). Theocolax elegans (pteromalid larval parasitoid). Predatory bugs (Xylocoris flavipes — anthocorid predator of eggs and larvae). Predatory mites (Cheyletus eruditus — predator of eggs). Parasitic nematodes (Steinernema carpocapsae — infects larvae inside pods). Entomopathogenic fungi (Beauveria bassiana, Metarhizium anisopliae — effective against adults). Natural enemies are most effective in unsprayed godowns. ICAR-NRCG Junagadh has evaluated several indigenous parasitoids for biocontrol of C. serratus in stored groundnut.
🌱 Host plants
- Groundnut (Arachis hypogaea — primary host). Tamarind (Tamarindus indica — original wild host in Africa; alternative host in India). Other Caesalpinioideae legumes — Bauhinia species, Cassia species, Caesalpinia species, Piliostigma species. The pest has strong preference for groundnut over alternative hosts when groundnut is available — but tamarind trees near groundnut godowns serve as persistent reservoirs of infestation.
🔄 Lifecycle
- Egg → Larva (4 instars, inside groundnut pod and seed) → Pupa (inside groundnut pod) → Adult.
- Females lay 50–150 eggs on the surface of groundnut pods.
- Eggs hatch in 5–7 days.
- Larvae bore THROUGH the pod shell INTO the seeds, feeding on the cotyledons for 25–35 days, moulting 4 times; each larva destroys 1–2 seeds.
- Mature larva pupates inside the hollowed-out pod; pupation lasts 8–12 days.
- New adults emerge by breaking through a characteristic large circular exit hole (3–5 mm) on the pod shell.
- Adults live 12–20 days (no functional mouthparts — do not feed); females begin oviposition within 24–48 hours of emergence.
- Total cycle 40–55 days at 30 °C; 4–6 overlapping generations per year in storage.
- Pest survives cold winter (December–February in north India) as diapausing larvae inside groundnut pods — diapause is triggered by low temperature and short photoperiod.
- Field infestation occurs during September–November (kharif groundnut harvest — adults emerging from storage infest maturing pods in the field) and April–May (rabi/summer groundnut harvest).
📅 Season
- Year-round activity in storage (controlled environment) — peak populations during April–June (warm pre-monsoon period — godown temperature 35–42 °C, ideal for rapid reproduction) and October–November (post-monsoon warm period — newly harvested kharif groundnut crop enters storage).
- Lower activity December–February (cool winter — godown temperature below 20 °C slows reproduction; pest survives as diapausing larvae inside groundnut pods).
- Field infestation occurs during September–November (kharif groundnut harvest) and April–May (rabi/summer groundnut harvest) — adults emerging from storage infest maturing pods in the field.
🔎 Appearance
- Medium-sized, robust, brownish chrysomelid beetle 5–7 mm long — larger than other bruchid pests of pulses.
- Body is oval, reddish-brown with characteristic greyish pubescence (fine hairs) covering the elytra and pronotum.
- The hind femora are strongly thickened and toothed — each femur has a series of 6–8 sharp teeth on the inner edge, used in male-male combat.
- Antennae are pectinate (comb-like) in males, serrate (saw-like) in females.
- The species name 'serratus' refers to the serrate female antennae.
- Larvae are white, legless, C-shaped grubs reaching 6–8 mm, with a small brown head capsule — they develop inside groundnut pods and seeds.
- Pupae are white, 5–6 mm, found inside the groundnut pod.
- Eggs are oval, yellowish, 0.8 mm, laid on the surface of groundnut pods.
💥 Damage level
- Severe
🔁 Reproduction rate
- Moderate
🗺️ Geographic regions
- Indian Subcontinent
- cosmopolitan. In India: All major groundnut-producing states — Gujarat (Junagadh
- Rajkot
- Amreli
- Jamnagar
- Bhavnagar)
- Andhra Pradesh (Anantapur
- Kurnool
- Chittoor
- Kadapa)
- Tamil Nadu (Thoothukudi
- Virudhunagar
- Ramanathapuram
- Sivaganga)
- Karnataka (Raichur
- Koppal
- Ballari
- Chitradurga)
- Maharashtra (Jalgaon
- Dhule
- Nandurbar
- Aurangabad)
- Telangana (Mahbubnagar
- Nagarkurnool)
- Rajasthan (Bikaner
- Nagaur
- Jaisalmer)
- Odisha (Bolangir
- Kalahandi). Pest is cosmopolitan — particularly damaging in tropical and subtropical groundnut-growing regions worldwide; native to Africa where it evolved on tamarind (Tamarindus indica).
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