Stored Product Pest

Bean Weevil

Acanthoscelides obtectus

Moderate Risk

Biology

A stout 3–4 mm olive-brown seed beetle clothed in mottled greyish hairs, with a short broad snout and short elytra that leave the tip of the abdomen exposed. Females lay eggs loosely among dry beans and a generation completes in about a month indoors.

Behaviour

Larvae bore into dry beans and develop entirely inside the seed, cutting a thin circular window before the adult pushes out through a neat round exit hole. Unlike field-only seed beetles it breeds continuously in storage, so a single infested bag can build for months.

Habits

Attacks kidney, navy, pinto and other Phaseolus beans in pantries, seed stores and warehouses. Infestations usually enter with beans already carrying eggs from the field. Warm rooms and long-held bags of dried beans are the conducive conditions.

Control methods

1Discard beans with round exit holes or powdery residue
2Freeze dried beans at -18°C for one week before storing
3Store beans in airtight glass or rigid plastic containers
4Buy in quantities that will be used within a few months
5Clean shelf cracks and vacuum spilled beans
6Keep seed stock separate from food stock
7Inspect new deliveries before shelving

Tailored to Bean Weevil

IPM Procedure Checklist

View full procedure

Step 1

Inspection

Inspect grain, spices, pet food and dry goods for larvae and webbing
Deploy pheromone monitors near storage and shelving
Check spillage in seams, cracks and shelf liners

Step 2

Identification

Confirm Bean Weevil (Acanthoscelides obtectus) — not a look-alike
Note life stage and risk level: Moderate
Capture clear photos and samples for the record

Step 3

Action Thresholds

Trigger action when monitor counts trend up
Re-evaluate weekly during active season
Document trigger criteria in the IPM plan

Step 4

Prevention

Rotate stock FIFO; reject damaged packaging at receiving
Store products in airtight containers
Maintain low humidity and clean storage surfaces

Step 5

Control Methods

Discard beans with round exit holes or powdery residue
Freeze dried beans at -18°C for one week before storing
Store beans in airtight glass or rigid plastic containers
Buy in quantities that will be used within a few months

Step 6

Monitoring & Evaluation

Service monitors on schedule and trend captures
Re-inspect for Bean Weevil activity at follow-up
Adjust tactics based on data; report findings to client