Monday, November 21, 2016

The most common grain weevils

Grain insects are widely distributed in all grains, cereal products, and animal feeds, and are very common where grain is stored (silos, warehouses, storage bins, barns, and houses).

Grain weevils are in the family Curculionidae and contain three highly changing pest species: Sitophilous oryzae (L.) rice weevils, S. granarius (L.) granary weevils and S. zeamais Motschulsky (maize weevils).

The rice weevil is the most common. Maize weevils are the less common. Adults are 0.3-0.6 cm in length and have an elongated snout containing the mouth parts that are typical of all weevils. Large numbers of them will appear whenever the stored produced is slightly disturbed. Grain weevils have a worldwide distribution but none thrive in tropical and subtropical regions.

Sitophilus granarius
All weevils have similar habits and inflict the same type of damage on grain. They attack primarily whole grain and seeds and typically do not reproduce on fine products such as flour, but can infest formed cereal products such as pasta. The female chews a hole into a kernel of grain, inserts her ovipositor and deposits an egg at the bottom of the hole.

As the ovipositor is withdrawn, she secreted a mucouslike substance that fills the hole to the surface of the grain and dries into hard plug which protects the egg and later the young larva desiccation.

Adults live a long time and females can lay a large number of eggs over their lifetime. Larvae develop and pupate within the seed and after eclosion adults chew out of the seed. Because larvae pupae and adults can occur inside whole kernels, these species can be more difficult to detect and this contribute to fragment counts in processed grain products.
The most common grain weevils
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