Pyrethrum

Pyrethrum is an insecticide that is extracted from the flowers of various Tanacetum species. The main active ingredients are pyrethrins, also cinerins and jasmolins.

Production

Pyrethrum is extracted from the dried flowers of Tanacetum species by crushing or extraction with solvents. The pulverized flowers arrived earlier in various forms of trade on the market. The only difference is in the chrysanthemum used as starting material. The " Montenegrin and Dalmatian insect powder " is ( cinerariifolium Tanacetum, syn. Chrysanthemum cinerariifolium, pyrethrum cinerariifolium ) from the Dalmatian insect flower, however, the " Armenian, Persian or Caucasian insect powder " from the Caucasian insect flower ( Tanacetum coccineum, syn. Chrysanthemum coccineum, pyrethrum roseum, pyrethrum carneum ) won.

Cultivation

To encourage flowering, the chrysanthemums need cold nights with temperatures less than 10 ° C. Commercial cultivation is therefore partly in temperate regions, such as Europe, Japan, or Tasmania. In the tropics, high altitude areas above 2000 m are also suitable for the cultivation of these plants. There they are grown mainly in Africa (among Tanzania, Kenya, Rwanda), South America (among Ecuador, Colombia) and New Guinea.

The plants are perennial. In Kenya, a pyrethrum planting is typically used three to four years. About one ton (dried ) chrysanthemum flowers is there harvested per hectare per year.

Economic Importance

The annual world production of dried pyrethrum flowers is on the order of 20,000 t. It can be about 500 t produced a 50% pyrethrin extract. The end-sales of manufactured products from this extract was estimated at 420 million U.S. $.

During 1983 Kenya and Tanzania supplied over 90 % of the world harvest today comes about a third of the world's supply of pyrethrum in Tasmania. The most important markets are the United States.

The cost of natural pyrethrum are high and the need for insecticides can not alone be covered. This meant that, starting from pyrethrum selective, highly potent compounds, known as pyrethroids, were developed that were suitable only for wide use in the veterinary and plant protection.

Effect

Pyrethrum acts as a contact poison, which is neurotoxic to insects. The mechanism of action based on the fact that the re-closing of voltage-gated sodium channels is prevented in the axon membranes, leading to neural its resting membrane potential can not build up again.

Pyrethrum is toxic to all species of insects, including beneficial insects. It is also highly toxic to fish. The LD50 for pyrethrin is in Rat (male ) oral 2.14 g / kg in female rats 0.7 g / kg, or when dermal absorption ( through the skin ) is more than 2 g / kg.

Pyrethrum decomposes under the action of sunlight and quickly loses its effectiveness.

Use

The effect of the extract was known to the Romans. They called pyrethrum " Persian insect powder " and used it against lice and fleas.

In Germany, Austria and Switzerland pyrethrum itself is not approved as an active ingredient in pesticides, however, exist in all these countries, approvals purified pyrethrum, the pyrethrins. Their use is also permitted in organic farming.

In the domestic sphere Pyrethrum is used

• In so-called electric vaporizers against flies and mosquitoes
• As insect sprays and strips against cockroaches, ants, etc.
• As a remedy for fleas and animal fleas, flea collar for dogs
• As a remedy for head lice ( " gold spirit forte ", " Jacutin N Spray ", " Infecto Pedicul " )