Weevil

The weevil is primarily a pest of the seed, with one seed supporting up to five larvae, although occasionally it may be found in the fruit flesh.
Background
Weevils are insects that feed on grains and other plant material. Like other insects, the life cycle of the weevil starts with an egg that is laid inside a grain or seed. When the larva hatches from the egg, it begins to feed on the material stored within the grain. After its pupal stage, the adult form of the insect emerges from the grain and begins the cycle again by mating and laying eggs. Weevils are considered to be serious agricultural pests because of the damage that they can cause to stored grain and seeds. A single female can lay up to 300 eggs at a time, depositing each individual egg into its own grain. Weevils can also be household pests, showing up in flour and cereals.

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The survival of an adult weevil is dependent, in part, on its exoskeleton or cuticle. The cuticle is composed of a mix of chitin and proteins that are organized into three layers, the epicuticle, the exocuticle, and the endocuticle. The cuticle goes through a hardening process known as sclerotization and melanization that requires the presence of the compound dihydroxyphenylalanine (DOPA). DOPA is synthesized from the amino acid tyrosine, which in turn, is synthesized from the amino acid phenylalanine. Phenylalanine is an essential amino acid.

The midgut of a weevil contains small pouches called caeca that function to increase the surface area of the gut, enhancing digestion and absorption of nutrients. At the tip of each caeca is a bacteriome, a specialized organ made up of cells called bacteriocytes, which protect endosymbiotic bacteria from exposure to the host’s immune system. Bacteriocytes not only house the endosymbionts in their cytoplasm, but they also provide nutrients required to support bacterial growth. In turn, gut endosymbionts are thought to aid in the digestion of grain and plant material consumed by the weevil. Bacteriomes containing endosymbionts are also found in reproductive tissues of the female weevil. While the bacteriomes associated with eggs and ovaries are present throughout the life of the weevil, those associated with the caeca are lost soon after the weevil completes its final adult metamorphosis.
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CONTROL METHODS FOR WEEVIL

Cultural Control

If the infestation is limited to 1 row or area, it may be advised to destroy that area, or to go out when they are most active (during the night), and pick the weevils off of the plants. You can also use sticky barriers to stop the beetles from travelling to new areas if the problem is in your garden. For preventative measures, substitute host plants for non-host plants the next time you decide to plant in that area.

Plant rotation can keep their population in check. Also, keep your gardens and fields weed-free and cultivate in the fall and winter. It is important to note that having satisfactory control is dependent on using an integrated management system that includes the use of cultural and chemical methods.

Chemical Control

Insecticides mixed with azadirachtin or pyrethrin can often provide sufficient control. Sometimes spot treatments are needed. The economic threshold to begin treatment is when at least 5 percent of young plants have been killed or wounded. When treating tobacco plants, use insecticides such as acephate, lambda-cyhalothrin, or lambda-cyhalothrin plus chloratraniliprole. Additionally, foliar insecticides that are put on your vegetable crops will also control the vegetable weevil. Be sure to carefully read the label for cautions and proper application.
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