Botanical Insecticides

These are pesticides derived or extracted from plants or plant parts. For control of ornamental insects and mites, pyrethrins, rotenone and neem (azadiractins) products are currently registered.

Pyrethrins

Pyrethrins are six related compounds extracted from dried flowers of the pyrethrum daisy, Chrysanthemum cinerariaefolium. When the ground up flower itself is used, the product is called a pyrethrum. Most products use pyrethrins combined with man-made synergists, usually PBO or MGK 264. These synergistic compounds increase the killing power of pyrethrins. Natural pyrethrum and pyrethrins are highly irritating to insect nervous systems and they cause quick "knockdown. " However, many insects are able to break down the pyrethrins before death occurs and soon recover. The synergists help stop this break down.

Mammalian Toxicity: Pyrethrins are low in mammalian toxicity, with the oral LD50 between 1,200 and 1,500. However, cats are highly susceptible to poisoning from pyrethrins. When ingested, pyrethrins are usually broken down by stomach acids before absorption can occur. Pyrethrins are general irritants and repeated contact may cause skin irritation or allergic reactions.

Uses: Pyrethrins are contact poisons with extremely short residual activity. Exposure to sunlight, air and moisture will degrade them within hours. Pyrethrins are generally mixed with a synergist and rotenone to provide better action against a wider variety of pests.

Rotenone

Rotenone is an alkaloid toxin extracted from the roots of two tropical legumes, Lonchocarpus from South America and Derris from Asia. Most of the current rotenone comes from Peru where it is often referred to as cube root. "Cube extracts" may appear on the label.

Rotenone is extracted with acetone or ether and the concentrate is used to make products. Some products simply use the powdered root.

Rotenone disrupts cellular respiration and death is relatively slow compared to most nerve toxins. Rotenone is extremely toxic to fish and is used as a fish poison by South American Indian or in water management programs. It is also synergized by PBO or MGK 264.

Mammalian Toxicity: Rotenone varies considerably in mammalian LD50 values (60-1,500) depending on the carrier used. Most ingested rotenone is detoxified efficiently via liver enzymes. Rotenone is more toxic by inhalation than by ingestion. High exposure may cause nausea, vomiting, muscle tremors and rapid breathing. Contact with rotenone may cause skin irritation and inflammation of mucous membranes.

Uses: Rotenone is a broad-spectrum contact and stomach poison that is most useful against leaf-feeding beetles and caterpillars. Rotenone degrades rapidly when exposed to air and sunlight. Alkaline materials, such as soaps, also speed rotenone degradation. Rotenone is usually mixed with Pyrethrins to provide longer lasting residual and better killing power.

Neem

Neem oil is an extract from the neem tree, Azadirachta indica, which is grown in tropical and subtropical climates. The most commonly used compound is azadirachtin, a complex chemical which acts as an insect feeding deterrent and growth regulator.

Azadirachtin can be extracted from much of the neem tree, but most comes from oil pressed from seeds and seed kernels.

When neem is applied to a plant it serves as a repellent, but if it is ingested, the compound affects insect egg laying and growth.

Mammalian Toxicity: Neem is very low in toxicity and has an LD50 near 13,000. It rarely causes any irritation to the skin or mucous membranes. It has been used in India and Asia as a cleaner, disinfectant and medicinal.

Uses: Currently registered products for ornamental pest control claim activity against a variety of sucking and chewing insects. Recent field trials have not confirmed significant repellency activity. However, good control of insects can be achieved if the insects are exposed while they are actively growing immatures - nymphs and larvae. Action can be slow because the insect often has to go through a molt or two.