Structure, Life Cycle and Economic Importance of Weevil/ Beetle


This  blog post provides readers with the following objectives. The reader will be able to:
o    Describe the external features and life cycle of the weevil.


Weevil/ Beetle

Phylum: Arthropoda
Class: Insecta

Order: Coleoptera

Habitat of Weevil

Weevils are often found in grain products, such as wheat, bean, rice, barley and corn.

The weevils form a large family of beetles.

Structure of Weevil

The weevil has a hard exoskeleton which is dark brown in color. It has three body division; the head, thorax and abdomen.

It has chewing mouthparts with well developed mandibles. The mouthparts are elongated and prolonged into a snout called rostrum. The main function of the rostrum is to bore holes in grains, where the female lays their eggs.

It has a pair of jointed bent or elbowed antennae, attached to the mid-length of the rostrum. The antennae end in knob called scape. 

The thorax is divided into the prothorax, mesothorax and metathorax. Each segment bears a pair of thick jointed walking legs. 

Weevil has two pair of wings. The forewings are hardened and leathery or thickened to form elytra (wing covers). These wings meet in a straight line down the middle of the back. The hind wings are membranous, and are used for flying. When the beetles are not flying, the hind wings are folded under the elytra.

Labelled structure of weevil

Larva of Weevil

Life Cycle of Weevil

Beetle develops by complete metamorphosis. That is, it has 4 developmental stages: egg, larvae, pupae and adult.

The female uses strong mandibles to chew a hole into a grain after which she deposits a single egg within the hole.

Weevil eggs hatch into soft, pale white or yellow, legless larvae called grubs, which eat the grain material surrounding them.

It pupates within the grain and emerges 2–4 days after hatching. During the pupal stage, it undergoes extreme changes that lead to the development of the adult.

When adult weevils are threatened or disturbed, they pull their legs close to the body and feign death.

Economic Importance of Weevil

1.   Destroy large quantity of grains during storage if not protected.

2.  Render grains useless both as seed and food.

3.  Presence in grains reduce economic value of the grains.

4.  Contaminate stored grains or seed with dead body remains or feces.

5.  Application of pesticides or insecticide in its control is expensive.

6.  Reduced the food content of the grains.

Control of Weevil

1.   Grains can be stored in container with tight lid.

2. Weevils can be controlled by using pesticides or spraying with DDT.

3.  Introducing organisms that are predators of the weevils.

4.   Early harvest of crop from fields.

5.  Grains like maize should be dry thoroughly under sunlight or by smoking


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