Field Pea Weevil
Bruchus pisorum
📖 Description
The Field Pea Weevil (Bruchus pisorum) is the single most destructive insect pest of field pea (Pisum sativum) worldwide and a major constraint on India’s rabi-season pea crop — the country produces ~600,000 tonnes of garden and field pea annually, concentrated in Uttar Pradesh, Madhya Pradesh, Rajasthan, Bihar, and the Himalayan hill states (Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Sikkim). The pea is the principal winter-season pulse of north India and a critical source of dietary protein in the vegetarian-leaning Indian diet; annual per-capita pulse consumption in India is ~18 kg, of which pea contributes ~1 kg. The weevil’s economic impact is two-fold: (1) direct weight loss and quality damage from larvae feeding inside the seed (each larva consumes 20–30 % of a single pea seed before pupating, and even a single infested seed in a sample downgrades the entire consignment), and (2) germination loss — infested seeds either fail to germinate or produce weak seedlings, directly reducing the next year’s crop stand. The pest’s biology is unusually specialised: the adult female lays eggs on the outside of the pea pod, and the hatching larva bores through the pod wall and into a developing seed, where it completes its entire development protected from any contact insecticide. Once the seed is harvested and stored, the adult emerges from a characteristic circular hole — at which point control is impossible except through fumigation. The species is also monophagous on Pisum: it does not attack other pulses (chickpea, lentil, mungbean, urdbean), making it the only pulse pest that is restricted to a single host genus. India’s seed-production programme for peas (run by the National Seeds Corporation and state seed corporations) maintains strict weevil-free certification standards — seed lots with >1 % infestation are rejected.
⚠️ Symptoms to watch for
- On the pea pod: a small circular bore hole sealed with a brownish plug of frass and plant tissue, often with a yellowish 'sting' mark visible on the pod wall where the female laid her egg. On the harvested seed: a circular emergence hole 2–4 mm diameter with characteristic jagged edges, and a hollowed-out interior containing the larval feeding cavity and frass. Even one infested seed in a sample downgrades the entire consignment; export markets have zero tolerance for live insects. India's pea production (~600,000 tonnes annually, concentrated in UP, MP, Rajasthan, Bihar, and the Himalayan hills) suffers 10–30 % field infestation and additional 5–15 % storage losses.
🩹 Treatment
- Cultural: harvest peas as soon as the pods turn yellow — early harvest catches the larva before it emerges from the seed. Storage fumigation: fumigate harvested seeds with aluminium phosphide at 1 tablet (3 g) per tonne in airtight storage for 7 days — kills all stages including larvae inside the seed. Chemical (field): spray dimethoate 30 EC at 1.5 ml/L at the early-flowering and pod-formation stages to kill adults before they oviposit — this is the only effective field intervention, because once eggs are laid inside the pod the larva is protected from any contact insecticide.
🌿 Organic treatments
- Early harvest (as soon as pods turn yellow — catches the larva before emergence); solarisation of harvested seeds by spreading them in thin layers on a black polythene sheet in direct sun for 4–6 hours (kills eggs and young larvae inside the seed through heat); cold treatment of seeds at -15 °C for 4 days (kills all stages — useful for small seed lots); application of inert dusts (diatomaceous earth at 1 kg/tonne seed — abrades the cuticle of emerging adults); planting resistant/tolerant pea varieties with low lectin content (e.g. 'Laxmi's Progress' lines); crop rotation with non-host crops (cereals, oilseeds) for 2 years.
🧪 Chemical treatments
- Dimethoate 30 EC @ 1.5 ml/L (field spray at flowering and pod-formation — kills adults), Lambda-cyhalothrin 5 EC @ 0.5 ml/L (field spray), Aluminium phosphide 3 g tablets @ 1 tablet/tonne (storage fumigation —kills all stages), Malathion 5 % DP @ 250 g/100 kg seed (storage protectant). Pre-harvest interval 21 days for field sprays; fumigated seed must be ventilated for 48 hours before consumption.
🛡️ Prevention
- Plant certified weevil-free seed — the single most important preventive measure, since the larva is already inside the seed at planting; harvest peas as soon as pods turn yellow — early harvest catches the larva before emergence; fumigate all stored pea seed with aluminium phosphide before storage; crop rotation with non-host crops (cereals, oilseeds) for 2 years to break the lifecycle; plough under crop residues immediately after harvest to bury emerged adults; avoid planting peas adjacent to last year's pea fields; plant early-maturing varieties (e.g. 'Arkel', 'Pusa Pragati') that escape the peak oviposition period.
🪴 Affected plants
- Field pea (Pisum sativum — primary host of economic importance); also on Pisum arvense (field pea), Pisum elatius (wild pea), and (rarely) sweet pea (Lathyrus odoratus) and other Lathyrus species. The pest is monophagous on Pisum — it does not attack other pulses.
🦋 Natural predators
- Egg parasitoids (Triaspis luteipes, Uscana senex — achieving 20–40 % natural parasitism in unsprayed fields), larval parasitoids (Anisopteromalus calandrae — also attacks stored-product beetles), predatory ants, spiders, ground beetles (Carabidae) that prey on adults on the soil surface, and insectivorous birds.
🌱 Host plants
- Pisum sativum (field pea — primary host), Pisum arvense (field pea), Pisum elatius (wild pea), Pisum humile (wild pea), Lathyrus odoratus (sweet pea — rare), Lathyrus sativus (grass pea — rare). Monophagous on Pisum.
🔄 Lifecycle
- Adult overwinters in crop residues, under bark, or in stored pea seed.
- In spring (Feb–March in north India), adults fly to pea fields and feed on pollen and petals before ovipositing.
- Female lays 200–400 small orange-yellow eggs singly on the outside of young pea pods.
- Egg stage 7–14 days.
- Larva bores through the pod wall into a developing seed, where it passes through 4 instars over 30–50 days, feeding entirely on the seed contents.
- Pupation inside the seed; pupal stage 8–14 days.
- Adult emerges from the seed through a circular exit hole either before harvest (in the field) or after harvest (in storage).
- Adult longevity 8–12 months (overwinters).
- One generation per year.
📅 Season
- Adults active during the pea flowering and pod-formation period (February–April in north India; April–June in the Himalayan hills).
- Larval development inside the seed continues through harvest.
- Adults emerge from stored seed from July onwards and overwinter until the next spring.
🔎 Appearance
- Adult is a chunky, dark brown to black weevil (Chrysomelidae: Bruchinae) with characteristic white, black, and grey mottling on the elytra and a small tooth on each hind femur; the head extends into a short broad snout.
- Larva is a small, C-shaped, white, legless grub with a dark brown head capsule, living entirely inside pea seeds.
- Adults are strong fliers and disperse widely between fields during the spring flowering period.
💥 Damage level
- Severe
🔁 Reproduction rate
- Slow
🗺️ Geographic regions
- Cosmopolitan in temperate and subtropical pea-growing regions globally; in India — Uttar Pradesh
- Madhya Pradesh
- Rajasthan
- Bihar
- Jammu & Kashmir
- Himachal Pradesh
- Uttarakhand
- Punjab
- Haryana
- Sikkim
- West Bengal (plains). Native to the Mediterranean region; spread globally via the pea trade.
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