Mungbean Bruchid (Adzuki Bean Weevil)
Callosobruchus chinensis
📖 Description
Callosobruchus chinensis — the Mungbean Bruchid or Adzuki Bean Weevil — is one of the most damaging stored-product insect pests of mungbean and adzuki bean in India, with economic significance centred on the pulse-producing belts of Rajasthan (Bikaner, Jodhpur, Nagaur), Madhya Pradesh (Indore, Ujjain), Maharashtra (Latur, Akola), Uttar Pradesh (Kanpur, Jalaun), Karnataka (Gulbarga, Bidar), and Andhra Pradesh (Kurnool, Anantapur). India is the world’s largest mungbean producer (~3 million tonnes from ~4 million ha) and the world’s largest pulse producer overall (~25 million tonnes); mungbean is a critical summer (spring) pulse crop providing dietary protein to India’s vegetarian population. The pest is native to Asia (likely China — the species name ‘chinensis’ refers to China, where it was first described) but has spread worldwide through the international pulse trade — it has been a major stored-pulse pest in India since ancient times (described in Sanskrit texts from ~500 BCE as ‘kalaya krimi’ — the pulse worm). The pest’s biology makes it particularly damaging: (1) adults do NOT feed — all damage is caused by larvae developing inside individual pulse seeds; (2) females lay 60–120 eggs glued to the surface of pulses — high reproductive potential; (3) larvae are concealed INSIDE individual seeds — protected from contact insecticides; (4) the species has a shorter lifecycle than C. maculatus (28–32 days vs 35–40 days at 30 °C), allowing more rapid population build-up at moderate temperatures; (5) the pest attacks maturing pods in the FIELD, allowing re-infestation of newly harvested crop — distinguishing it from C. maculatus which is essentially storage-only; and (6) high insecticide resistance — the pest has documented resistance to organophosphates, pyrethroids, and even aluminium phosphide fumigation in some Indian populations. The economic impact is severe: heavy infestations can destroy 40–70% of stored mungbean and adzuki bean seeds within 4–6 months of storage. With mungbean valued at ₹80–150 per kg, even moderate infestations cause disproportionate economic loss — for a typical Indian pulse grower storing 1 tonne of mungbean for 6 months (waiting for higher off-season prices), a severe C. chinensis infestation can wipe out ₹15,000–30,000 of income. Management is best achieved through IPM combining sun-drying to <10% moisture, hermetic storage bags (PICS bags), godown hygiene, threshold-based fumigation (aluminium phosphide), diatomaceous earth application, regular inspection, FIFO stock rotation, sealed storage containers, and limited-duration storage. The species often co-occurs with C. maculatus in the same pulse lot — competition between the two species has been extensively studied as a model system in community ecology. The competitive outcome depends on temperature: C. chinensis dominates at moderate temperatures (25–30 °C) due to its shorter lifecycle and higher reproductive rate, while C. maculatus dominates at higher temperatures (32–35 °C) due to its higher thermal tolerance. This temperature-dependent competition has been documented in Indian pulse godowns — C. chinensis is more common in winter-stored pulses (December–February) while C. maculatus dominates in summer-stored pulses (April–June).
⚠️ Symptoms to watch for
- Adults emerge from stored pulses, mate, and females lay 60–120 eggs glued to the surface of pulses. Larvae hatch in 4–5 days and immediately bore INTO the pulse seed — creating a characteristic 'window' (a thin layer of seed coat over the larval entry hole). Larvae feed inside the seed for 15–20 days, consuming the cotyledons and reducing the seed to a hollow shell filled with frass. Adult emergence leaves a characteristic circular exit hole (1.5–2.5 mm) on the seed surface. Heavy infestations can destroy 40–70% of stored mungbean and adzuki bean seeds within 4–6 months of storage. The species is especially damaging to mungbean — a high-value pulse valued at ₹80–150 per kg — and can render entire lots unfit for human consumption due to frass, insect fragments, and uric acid contamination. The pest also attacks maturing pods in the field, allowing re-infestation of newly harvested crop.
🩹 Treatment
- Fumigate stored pulses with aluminium phosphide (Celphos) at 1 tablet (3 g) per tonne of pulses for 72 hours in a sealed godown — kills all stages including eggs inside seeds. Apply malathion 5% DP at 250 g per 100 kg of pulses — contact insecticide dust. Apply deltamethrin 2.8 EC at 0.5 ml/L as a surface spray on godown walls and floors. Apply spinosad 240 SC at 0.5 ml/L — reduced-risk insecticide. Apply diatomaceous earth (SilicoSec) at 1 kg per tonne of pulses — physical desiccant. Sun-dry pulses to moisture content <10% 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 pulses; 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 pulses to <10% 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 pulses with 5–10 ml of edible oil (groundnut, coconut, mustard) per kg; suffocates eggs and larvae. Sand or ash admixture — mix equal volume of clean dry sand or wood ash; prevents adult oviposition.
🧪 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 pulses; contact organophosphate; restricted in some states due to pest resistance. 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 pulses; pyrethroid dust. Avoid applying insecticides directly to pulses meant for human consumption. Rotate IRAC groups to prevent resistance.
🛡️ Prevention
- Sun-dry pulses to moisture content <10% before storage. Inspect all incoming pulse 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 pulses monthly; remove infested lots immediately. Store pulses in sealed plastic or metal containers (not jute bags). Maintain first-in-first-out (FIFO) stock rotation. Avoid storing pulses for more than 6 months. Use cold storage for high-value pulse seed. Maintain 100 m isolation between pulse storage godowns and processing units. Apply threshold-based fumigation (1 adult per kg of pulses).
🪴 Affected plants
- Mungbean (Vigna radiata — primary host, gives the species its common name 'Mungbean Bruchid'). Also on adzuki bean (Vigna angularis — gives the alternative name 'Adzuki Bean Weevil'), black gram (Vigna mungo), cowpea (Vigna unguiculata), chickpea (Cicer arietinum), pigeonpea (Cajanus cajan), lentil (Lens culinaris), pea (Pisum sativum), and other pulses. In India, the pest is most damaging in pulse-producing belts of Rajasthan (Bikaner, Jodhpur, Nagaur), Madhya Pradesh (Indore, Ujjain), Maharashtra (Latur, Akola), Uttar Pradesh (Kanpur, Jalaun), Karnataka (Gulbarga, Bidar), and Andhra Pradesh (Kurnool, Anantapur). The species often co-occurs with C. maculatus in the same pulse lot — competition between the two species usually results in C. chinensis dominance at lower temperatures and C. maculatus dominance at higher temperatures.
🦋 Natural predators
- Anisopteromalus calandrae (pteromalid pupal parasitoid — also attacks stored-product pests; under evaluation by NBAIR Bangalore). Dinarmus basalis (pteromalid larval-pupal parasitoid — the most important natural enemy; under evaluation by IIPR Kanpur). Lariophagus distinguendus (pteromalid larval parasitoid — attacks larvae inside pulse seeds). 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 seeds). Entomopathogenic fungi (Beauveria bassiana, Metarhizium anisopliae — effective against adults). Natural enemies are most effective in unsprayed godowns.
🌱 Host plants
- Mungbean (Vigna radiata — primary host). Adzuki bean (Vigna angularis), black gram (Vigna mungo), cowpea (Vigna unguiculata), moth bean (Vigna aconitifolia). Chickpea (Cicer arietinum), pigeonpea (Cajanus cajan), lentil (Lens culinaris), pea (Pisum sativum). Soybean (Glycine max — generally resistant).
🔄 Lifecycle
- Egg → Larva (4 instars, inside pulse seed) → Pupa (inside pulse seed) → Adult.
- Females lay 60–120 eggs singly or in small clusters, glued to the surface of pulses.
- Eggs hatch in 4–5 days.
- Larvae bore INTO the pulse seed, feeding on the cotyledons for 15–20 days, moulting 4 times; each larva destroys one pulse seed.
- Mature larva pupates inside the hollowed-out seed; pupation lasts 5–8 days.
- New adults emerge by breaking through a characteristic 'window' on the seed surface.
- Adults live 5–10 days (no functional mouthparts — do not feed); females begin oviposition within 24 hours of emergence.
- Total cycle 24–32 days at 30 °C; 6–10 overlapping generations per year in storage.
- Pest survives cold winter (December–February in north India) as diapausing larvae inside pulse seeds — diapause is triggered by low temperature and short photoperiod.
- Field infestation occurs during March–April (rabi pulse harvest) and September–October (kharif pulse harvest) — adults emerging from previous year's storage infest maturing pods in the field.
📅 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 pulse crop enters storage).
- Lower activity December–February (cool winter — godown temperature below 20 °C slows reproduction; pest survives as diapausing larvae inside pulse seeds).
- Field infestation occurs during March–April (rabi pulse harvest — adults emerging from storage infest maturing pods in the field) and September–October (kharif pulse harvest).
🔎 Appearance
- Small, robust, reddish-brown chrysomelid beetle 2.5–3.0 mm long — slightly smaller than the related C.
- maculatus.
- Body is oval, reddish-brown with characteristic dark brown to black markings on the elytra — the pattern includes two pairs of dark spots on each elytron, giving a '4-spotted' appearance.
- Antennae are pectinate (comb-like) in males, serrate (saw-like) in females.
- Legs are reddish-brown with strongly toothed hind femora.
- The species is morphologically distinguished from C.
- maculatus by smaller size, more reddish coloration, and the specific elytral pattern.
- Larvae are white, legless, C-shaped grubs reaching 3.5–4.5 mm, with a small brown head capsule — they develop entirely INSIDE individual pulses.
- Pupae are white, 2.5–3.5 mm, found inside the pulse seed.
- Eggs are oval, yellowish, 0.5 mm, glued singly or in small clusters to the surface of pulses.
💥 Damage level
- Severe
🔁 Reproduction rate
- Fast
🗺️ Geographic regions
- Indian Subcontinent
- cosmopolitan. In India: All major pulse-producing states — Rajasthan (Bikaner
- Jodhpur
- Nagaur)
- Madhya Pradesh (Indore
- Ujjain
- Vidisha)
- Maharashtra (Latur
- Osmanabad
- Akola)
- Uttar Pradesh (Kanpur
- Jalaun
- Banda)
- Karnataka (Gulbarga
- Bidar
- Bijapur)
- Andhra Pradesh (Kurnool
- Anantapur
- Prakasam)
- Tamil Nadu (Dharmapuri
- Krishnagiri)
- Gujarat (Banaskantha
- Mehsana)
- Punjab (Bathinda
- Ferozepur)
- Haryana (Hisar
- Sirsa)
- Bihar (Patna
- Nalanda). Pest is cosmopolitan — particularly damaging in Asian pulse-growing and pulse-storing regions.
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