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Food-Infesting Weevils and Their Control

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Food-Infesting Weevils and Their Control

Rice Weevil

by Olaf Leillinger

Weevils. Even the name can cause a shudder in anyone who has ever had these ugly, snout-nosed, insects in their flour, rice, or cornmeal.

Often called flour bugs, because that is where they are frequently found, there are actually a number of types of weevil, including the seed weevils, granary/grain weevils, rice weevils, maize weevils, and bean/pea/seed weevils, but the "true" weevils - with the snout nose, are the granary, rice, and maize weevils.

Similar to other pantry pests, granary and rice weevils will infest and feed on whole grains and rice as well as nuts, beans, cereals, seeds, corn, and other such foods.

But unlike beetles that live and feed on foods, these weevils actually live and feed inside the food:

  • The female chews a hole into a seed or grain kernel and deposits an egg inside.
  • The female weevil then seals up the opening, leaving the egg inside.
  • When the egg hatches (inside the grain/seed), the larva feeds on the meat inside until it is fully grown.
  • Once fully grown, the adult weevil eats its way out of the grain/seed.
  • Because the females emit pheromones, male weevils will be waiting outside the hole for her to emerge, and will immediately seek to bond with her to reproduce.

Weevil Identification

  • Weevils are 1/8- to 1/4-inch long.
  • They are most easily distinguished by their long snout.
  • They can live up to 8 months, and may venture far from the food originally infested.

The Rice Weevil

  • Very tiny, this weevil is only about 1/16-inch long.
  • The adult is dull reddish-brown to black, with four reddish-yellow spots on its back.
  • The larvae are soft, white grubs with no legs. Pupae are similar to adults with long snouts, but they are white.
  • The adult rice weevil can fly.
  • The adult can live up to five months, with the female laying up to 400 eggs during her lifetime.

The Maize weevil

  • Long thought to be simply a larger strain of rice weevil, the maize weevil is very similar in looks.
  • It is slightly larger, up to 1/8-inch long.
  • Like the rice weevil, it is dull reddish brown to black with four red-yellow spots on its back - however its coloring is generally darker than that of the rice weevil.
  • The rate of development is slightly slower for the maize weevil than for the rice weevil.
  • Like rice weevil, its larvae are soft, white grubs with no legs. Pupae, too, are similar to adults with long snouts, but they are white.
  • It, too, can fly.

The Granary Weevil

  • The granary weevil is more cylindrical than the rice or maize weevil.
  • It is about 1/5-inch long.
  • Its coloring is similar to the rice and maize weevils - reddish brown to black.
  • At about 1/4 its body length, the granary weevil's long snout extends down from its head.
  • Its larvae (soft, white grubs without legs) and white pupae are similar to those of the rice and maize weevil.
  • This weevil cannot fly, so will be found close to the areas it infests.
  • The adults can live up to eight weeks, during which time the female can lay up to 200 eggs.

Partly because of its long life and partly because of its ability to fly, the rice weevil is considered to be the most destructive, but all three weevils can cause extensive damage to stored foods. When they infest grain that is stored in bins and remains undisturbed, they can completely destroy the commodity.

In the home, the weevils can be brought in on packaged foods or they can come in from outside. Once inside, a population can grow and expand to food items stored nearby if they are not controlled.

Part 2. Control Stored-Food Weevils

References

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