Inorganic insecticides

Inorganic insecticides have a long history of use in household and stored-food pest control: this group includes arsenic, boron, mercury, and sulfur. They are stable compounds and toxic to a broad range of animals. Sulfur is one of the oldest pesticides, and is toxic as a contactor stomach poison to mites, spiders, and scale insects, and as a stomach poison for some caterpillars. Sulfur dusts and sprays are also fungicidal.

Arsenic-based pesticides are stomach poisons and are typically used for insect and rodent control. The most common compounds are lead and calcium arsenate; calcium is the most toxic to insects and mammals. Arsenic trioxide dust is used for termite control. Arsenic compounds have a complex mode of action. They uncouple oxidative phosphorylation (by substitution of the arsenite ion for the phosphorus), which is a major energy-producing process of the cell. The arsenate ion inhibits certain enzymes that contain sulfhydryl groups and both the arsenite and arsenate ions coagulate proteins.

Boron compounds have a long history in household insect control as nonselective insecticides. The mode of action is a stomach poison when a lethal dose is ingested. The target sites may be the mid- and hindgut; in the hindgut borates may disrupt water regulation. Borates are also used as a contact poison because borate dusts absorb insect cuticle wax. Surface applications of boric acid and water dilutions of borates act as antiphagostimulants for insects such as wood-infesting beetles and termites. Boron is toxic to animals and humans, and the tolerable daily intake is 24 mg/day. It is a nonmetallic element that is naturally combined with oxygen and other elements, such as sodium and calcium. Boric acid is a commonly used boron compound. Itis a white crystalline solid with a maximum solubility in water of 6%, and it is nonvolatile with a long residual activity. It is primarily a slow-acting stomach poison, but it is capable of penetrating insect cuticle. Borax is a naturally occurring sodium tetraborate and as an insecticide it is used in powder form or dissolved in water. Water-soluble polyborates, such as disodium octaborate tetrahydrate, are effective in protecting wood from some wood-infesting insects, such as termites, carpenter ants, and beetles.

Amorphous silicon dioxide hydrate (silica gels or silica aerogels) is made from a geological deposit composed of fossilized skeletons of siliceous marine and freshwater animals, particularly diatoms and other algae. These skeletons are made of hydrated amorphous silica and, when crushed, they break up into fine, talc-like fragments. This material has a large specific surface area of 300 m2/g, and individual particles are 0.010.05 /m diameter. Silica gels that have low bulk density and high porosity are called aerogels. The mode of action is based primarily on the ability of this material to adsorb waxes from insect cuticle, which permits excess water loss from the body. Silica may be abrasive to the cuticle, which further increases water loss. Mortality is due to desiccation, which is a result of abrasion and damage to the protective wax layer in the cuticle. Insect movement and other activities gradually decline until death occurs. These compounds are also repellent to some insectspecies. To increase efficacy and reduce the disadvantage of the extremely lightweight of silica aerogels, the dusts are typically formulated with an isoparaffinic petroleum oil (solvent), pyrethrins, and a synergist. Diatomaceous earth is primarily silica; itacts as an abrasive and is slightly sorptive. Ithas only limited ability to adsorb the solid wax from an insect cuticle. Insects vary widely in their response to dust desiccants. Some species have a protective (cement) layer in the cuticle, which is secreted by cells in the epidermis; this appears to provide some protection against dust desiccants. It is well developed in the cuticle of many species of beetles.

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Responses

  • jay orosco
    What is the more of action of arsenic, boron, borates and silica gel?
    2 years ago
  • arnor lightfoot
    Do silica stop water loss in cuticle of insect?
    2 years ago

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