Weevils

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Granary and Rice Weevils are considered one of the most devastating stored product pests found in the United States.

Fast Facts

Color Granary weevils are uniformly colored dark brown-black with no spots. Rice weevils are dark brown with four light colored spots on its back.
Size They are about 2.5 – 5 mm in length.
Appearance The adult granary weevil is a shiny, reddish-brown with elongated pits on the thorax, whereas the adult rice weevil is a dull, reddish-brown with a slender, hard-shelled body that appears pitted or scarred with tiny holes. Both weevils in the larval stage are legless, humpbacked, white/creamy white, with a small, tan head. Weevils in the pupa stage have long, slender snouts like the adults.
Granary weevil control and removal - Batzner Pest Control in Wisconsin
Granary Weevil
Rice weevil control and removal - Batzner Pest Control in Wisconsin
Rice Weevil

Diet

Both larvae and adults feed on grain products including rye, barley, buckwheat, beans, stored cotton, cashews, cereals, pasta and birdseed.

Habitat

Most of their life is spent within the grain kernel. Emergence holes of the rice weevil are smaller than those of the granary weevil, and tend to be smooth and round. There is generally no external evidence that the larvae have been eating and growing inside the seed until after about one month when the adult weevil chews through the seed coat and emerges.

Life Cycle

The egg, larva, and pupa stages of weevils occur in the grain kernels and are rarely seen. Females drill a tiny hole in the grain kernel, deposit an egg in the cavity, then plug the hole with a gelatinous secretion. The egg hatches into a young larva which bores toward the center of the kernel, feeds, grows, and pupates there. New adults bore emergence holes from the inside, then leave to mate and begin a new generation. Emergence holes of the granary weevil are fairly large and tend to be more ragged than smooth and round.

Rice Weevil
Female rice weevils lay between 300 and 400 eggs, with the life cycle requiring about 32 days for completion. Two larvae can develop in one wheat kernel.

Granary Weevil
The life cycle is about 30 to 40 days during the summer, and 123 to 148 days during the winter, depending on temperature.

Signs of Infestation

There is generally no external evidence that the larvae have been eating and growing inside the seed until after about one month when the adult weevil chews through the seed coat and emerges.

Containers

Look in unsealed food containers, where the presence of warm grains near the surface may indicate a rice weevil problem.

Holes in grain bags

Holes in stored grains may also signal an infestation of weevils.

Heat

In grain silos, elevators and other storage facilities, infested grains may feel heated near the surface.

Moisture

Grains may be damp to the point that molds and fungi start to appear.

Kernels

Damaged kernels may also indicate a weevil infestation as does the sight of recently emerging adults.

Flying

Rice weevils are excellent fliers, though they may fall to the ground and feign death when startled.

Light

Finding the pests near a source of light may also denote a possible infestation.

Damage

Damage is caused primarily by the larvae but also by the adults. In undisturbed environments with the right conditions, rice weevils can almost completely destroy entire elevators or bins of stored grain. Their ability to fly only exacerbates the problems they cause. The pests develop within the grain itself, leaving behind hollowed-out kernels that can no longer be used.

Prevention & Control

Weevils Prevention

Storage Bins: Keeping storage bins properly sanitized may be the best way to avoid weevils. Removing all old grain and dust before putting in new items can help cut down on potential incursions. Additionally, any spilled grains should be removed immediately.

Cracks: Treat and seal all cracks, crevices and other points of entry.

Insecticide: Approved insecticides may be used but only when handled by a knowledgeable individual like a trained pest control professional.

Rotate food: Rotate product with consistency using old food items before new ones to help reduce the risk of a weevil infestation.

Weevils Control
  • Cupboards or shelves holding infested items should be emptied and thoroughly vacuumed, especially the cracks and corners.
  • All products containing or made of whole grains need to be inspected. Discard infested foods in outdoor trash. Infested decorations (flowers, wreaths, etc.) should also be discarded.
  • Store all dried food, including dried pet foods and birdseed, in a glass or plastic container with a tight lid. This will contain the infestation if one is present.
  • Consume older food products prior to newer purchases of the same food. Products purchased in larger quantities (e.g., from a wholesale food warehouse) are more likely to become an infestation source if these are stored for long periods of time – especially if they are not stored in containers with tight-fitting lids.

As weevils reproduce inside of grains, the cost of trying to eradicate an infestation without professional assistance may end up being as high as the cost of losing the stored product itself.

If a weevil infestation occurs, count on a professional pest management service to take care of the problem knowledgeably and successfully.