Pulse beetles (bruchids)

Callosobruchus maculatus and Callosobruchus chinensis Callosobruchus maculatus (Fabricius, 1775); Callosobruchus chinensis (Linnaeus, 1758) · formerly or also: Bruchus maculatus, Chinese bruchid (C. chinensis)

cowpea weevil (Callosobruchus maculatus) · English, Worldwide
दाल का घुन (dal ka ghun) · Hindi, North India
bruche du niébé · French, West Africa

Pulse beetles are small beetles whose grubs develop inside stored seeds of cowpea, chickpea, mung bean, black gram, pigeon pea, lentil and other pulses. Each infested seed ends up with a round exit hole, loses weight and often cannot germinate. Infestation starts in the field on ripening pods and multiplies quickly in storage, so unprotected cowpea can be destroyed within a few months. Airtight (hermetic) storage is one of the simplest and most effective controls.

Female pulse beetle (Callosobruchus maculatus) on a stored seed. Photo: limbatus, CC BY 2.0, via Wikimedia Commons.

Type: Insect · Insect (seed beetle; the grubs develop inside seeds)
Classification: Animalia › Insecta › Coleoptera › Chrysomelidae (subfamily Bruchinae)
Main crops: Cowpea, Chickpea, Mung bean, Black gram, Pigeon pea, Lentil, Adzuki bean, Stored grain
Found in: Africa, South and East Asia, Americas and Europe, Oceania
Chemical groups: IRAC 24A, IRAC 3A (mode-of-action groups, not products)
Last reviewed: 2026-10-20

Pulse beetles scientific name, order and family

The scientific name of pulse beetles is Callosobruchus maculatus and Callosobruchus chinensis Callosobruchus maculatus (Fabricius, 1775); Callosobruchus chinensis (Linnaeus, 1758), in the order Coleoptera, family Chrysomelidae (subfamily Bruchinae).

Older or alternative scientific names: Bruchus maculatus, Chinese bruchid (C. chinensis).

Where it occurs

Found worldwide in tropical and subtropical regions and in stores of imported pulses elsewhere; both species have spread with the trade in pulses.

Region	Status
Africa	Widespread; C. maculatus major in cowpea
South and East Asia	Both species widespread
Americas and Europe	Present in stores
Oceania	Present

Symptoms and identification of pulse beetles

White eggs of Callosobruchus maculatus glued to cowpea and adzuki bean seeds. Photo: limbatus, CC BY 2.0, via Wikimedia Commons.

The organism

Adults are about 2-4 mm long, reddish-brown to dark, with short wing covers that leave the tip of the abdomen exposed; C. maculatus has two large dark patches on the wing covers. Adults live only about one to two weeks and do not need to feed. Eggs are tiny, white and glued onto the seed surface, where they look like white specks.

Signs in the crop, stage by stage

Crop stage	What you see
Field (mature pods)	Eggs on dry pods and seeds; infestation carried unseen into storage.
Storage	White eggs glued to seeds; round 'windows' in the seed coat where adults are about to emerge; round exit holes; live beetles running on the surface of stored grain.
Severe infestation	Seeds riddled with holes, powdery and light; warm, damp grain; loss of germination and food value.

Life cycle of pulse beetles

Life cycle of Pulse beetles (bruchids) — diagram drawn by Laisha from the stages below. Durations depend on temperature.

Females glue eggs singly onto seeds. The grub bores straight into the seed and feeds and pupates inside. The adult cuts a round window and emerges, mates and lays eggs within a day or two, so populations multiply rapidly in storage.

Stage	Duration	Notes
Egg (glued to seed)	About 4-6 days	White specks.
Larva (inside seed)	About 2-3 weeks	Hidden from contact treatments.
Pupa (inside seed)	About 5-7 days	Under a thin window.
Adult	About 1-2 weeks	Females lay 50-100 eggs.

Temperature

One generation takes about three to five weeks at 25-30 °C and high humidity; development slows greatly in cool, dry storage.

Generations

Many generations per year in warm stores.

Conditions that favour it

Warm, humid storage; seed stored in open sacks or baskets; mixing new and old stocks; late harvest that allows field infestation; and dirty stores with old infested seed.

Economic threshold level (ETL)

There is no field threshold; any infestation in stored seed grows quickly, so management is preventive from harvest onward.

Damage and yield loss from pulse beetles

Unprotected cowpea can lose much or all of its value within three to six months of storage; infested seed loses weight, nutritional value, germination and market price.

Monitoring

Check samples of stored seed every few weeks for white eggs, round windows and exit holes.
Look for live beetles on the surface of the store and in sacks.
Inspect seed at harvest for eggs from field infestation.

How to control pulse beetles (integrated management)

Control works best as a sequence: prevent, monitor, then act only when a threshold or a risk forecast says so, using the least disruptive option that works.

Cultural control

Harvest promptly when pods are dry and thresh and dry seeds well before storage.
Clean stores, sacks and containers, and never mix new seed with old infested stocks.
Store seed in airtight (hermetic) containers, such as triple-layer hermetic bags, sealed drums or well-sealed pots, which kill insects by lack of oxygen.

Mechanical and physical control

Sun-heating (solarising) seed in a thin layer under clear plastic kills eggs and grubs; mixing seed with fine ash, sand or a small amount of vegetable oil protects small household stocks.

Biological control

Parasitic wasps such as Dinarmus basalis and Anisopteromalus calandrae attack bruchid grubs inside seeds and can reduce populations in stores.

Host resistance

Some cowpea and mung bean varieties have seeds that resist bruchids; resistance is partial.

Chemical control of pulse beetles — by mode-of-action group only

Laisha names chemical options only by their resistance-committee mode-of-action group (IRAC for insects, mites and nematodes, FRAC for fungi, oomycetes and bacteria, HRAC for weeds), never by active ingredient or product. What is registered differs by country and changes over time; the label and your local plant-protection authority decide what may be used, on which crop, at what rate and with what pre-harvest interval.

Fumigation and grain protectants are used in commercial stores and must be applied only by trained people because of health risks; hermetic storage avoids chemicals altogether. What is registered differs by country and changes over time; follow the label and your local plant-protection authority.

Scheme	Group	Mode of action	Notes
IRAC	24A	Mitochondrial complex IV electron transport inhibitors (phosphides), fumigation	Highly toxic; trained applicators only; resistance reported.
IRAC	3A	Sodium channel modulators (pyrethroids), grain protectant	Where registered for stored pulses.

Resistance management

Fumigate only in gas-tight conditions for the full exposure time to avoid selecting resistance, and use hermetic storage and hygiene wherever possible.

Look-alikes and how to tell them apart

Bean weevil (Acanthoscelides obtectus) — Greyish bruchid mainly in stored common beans, with several larvae per seed.
Larger grain borer — Cylindrical beetle that bores into stored maize and cassava, producing much dust.
Rice weevil and maize weevil — Weevils with a long snout, attacking cereal grains rather than pulses.

Host range

Stored seeds of cowpea, chickpea, mung bean, black gram, pigeon pea, lentil, adzuki bean and other pulses; C. chinensis has a somewhat wider range and also attacks peas and beans.

What is still uncertain

Field infestation levels at harvest vary greatly and are rarely measured.
Resistance to fumigants in bruchids is less documented than in cereal pests.

Grow guides for its host crops

How to grow the crop well is the first line of defence. Laisha's free grow guides cover each crop from sowing to harvest:

How to grow Cowpea How to grow Chickpea How to grow Mung bean How to grow Black gram How to grow Pigeon pea How to grow Lentil How to grow Adzuki bean

Not sure this is what you are seeing?Ask Laisha: describe the symptoms or send a photo, and get a reasoned first read with what to check next — for your crop, your stage and your region.Ask Laisha

Sources

Callosobruchus maculatus (cowpea weevil) datasheet — CABI Compendium. https://doi.org/10.1079/cabicompendium.10987
Callosobruchus chinensis (Chinese bruchid) datasheet — CABI Compendium. https://doi.org/10.1079/cabicompendium.10986
Life history parameters of the parasitoid wasp Anisopteromalus calandrae parasitising Callosobruchus — Journal of Stored Products Research (Elsevier). https://doi.org/10.1016/j.jspr.2024.102539
Evaluation of hermetic storage bags for the management of pulse beetle, Callosobruchus maculatus, in chickpea — The Journal of Research ANGRAU. https://doi.org/10.58537/jorangrau.2023.51.4.02
Profitability of hermetic Purdue Improved Crop Storage (PICS) bags for African common bean producers — Gates Open Research. https://doi.org/10.21955/gatesopenres.1115521.1

Written by Laisha from the sources above, in its own words. This page is general reference, not a prescription: confirm identification locally and follow the label and your plant-protection authority.