Pyrethrum is a natural insecticide product derived from Chrysanthemum plants commonly used on a wide range of insect pests such as ants, mosquitoes, fleas, and aphids. Pyrethrin’s, the naturally occurring organic compounds found within the flowering heads of Chrysanthemum plants, are derived and extracted to produce the insecticide as they provide the insecticidal properties which target the insects’ nervous system.The natural properties and effectiveness of Pyrethrum make it a popular choice as both a home and agricultural insecticidePyrethrum has been used as an insecticide for centuries, Aromaticia (2004) states that the first recorded use dates back to Persia 400BC where crushed Chrysanthemum flowers were used as a household insecticide. Yet it wasn’t until around 1800 that pyrethrin’s, the compounds found in Chrysanthemum flowers, were identified as being responsible for the flower’s insecticidal properties (Gunasekara, 2004).
According to the National Pesticide Information Center (2014), these pyrethrin’s were first registered for use as an insecticide in the 1950s, furthermore, they state that there are currently 2,000 registered products containing pyrethrin compounds which include, sprays, dusts, pet shampoos and bug bombs.The modern-day production of pyrethrum occurs on a mass commercial scale, yet the process remains relatively unchanged. The production process of pyrethrum insecticides involves the extraction of pyrethrin’s from the harvested flowering heads of plants from the Chrysanthemum genus.
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The species Chrysanthemum cinaerariifolium, otherwise known as the Dalmatian Chrysanthemum, are the most commonly used for the production of the insecticide due to their high pyrethrin concentration (Duval, 1993)The desired cultivation site of C. cinaerariifolium, takes place within an altitude range of 3000-6000 meters above sea level as research has shown that pyrethrin concentration increases as elevation levels increase. Therefore, the majority of commercial cultivation occurs in mountainous equatorial zones, such as Kenya and Ecuador, where the warm weather assists in quickly drying the cultivated flower heads. (Anonymous, 1987)The insecticidal pyrethrin compounds, are contained within the seed cases of c. Cinaerarilifolium therefore they must be extracted to release there insecticidal properties.
To extract them from these cases, the harvested flowers must be dried and crushed to produce a powder. The resulting powder contains many impurities from the original flower, therefore only around 30% of the pyrethrum powder contain the active pyrethrin compounds. Alternatively, solvents can be used on the harvested blooms to extracts the natural oils from the within the flower to produce an insecticide solution. (Extension Toxicology Network, 1994)Pyrethrum is a mixture of six pyrethrin compounds which are toxic to insects. These six compounds are Pyrethrin I and II, Cinerin I and II and Jasmolin I and II, collectively called pyrethrin’s.
These pyrethrin’s are contact poisons which work by quickly penetrating the insect’s nervous system, delaying the closure of voltage gated sodium channels which increase the sodium ion permeability and depolarization of the nerve cell membrane. The hyperexcitability of the membrane prevents the repolarization of the nerve cell, generating paralyses and ultimately causes death (Emyr Davies et al. 2016).
However, even if the insecticide has been successfully applied, enzymes within the insects can detoxify the pyrethrin compounds from its system, leaving the insect unharmed, rendering the insecticide ineffective. (Extension Toxicology Network 1994)Consequently, to increase their effectiveness, Pyrethrin’s are often mixed with other chemicals, called synergists which delay enzyme action so a lethal dose is assured. Moreover, this supports the application of lower doses to achieve the same result (Extension Toxicology Network 1994) A common example of a synergized pyrethrin is the combined use of pyrethrin with the synthetic compound piperonyl butoxide. Despite having no insecticidal properties itself, piperonyl butoxide acts as a synergist to pyrethrin by inhibiting the insects primary detoxification route, cytochrome P-450, which facilitate the oxidative breakdown of pyrethrin’s (Casida, 1970).
As a result, this enhances the effectiveness of the insecticide, speeding up the toxic process, in comparison to the lone use of pyrethrin’s. Furthermore, Man-made synthetic insecticides called pyrethroids, have been synthesized based upon pyrethrin’s natural properties to further combat insects by acting as a more effective insecticideNevertheless, despite being less effective, the natural insecticide pyrethrum is regarded as better for environment as oppose to synthetic pyrethroids. The naturally derived pyrethrin’s are chemically unstable in the natural environment where they break down rapidly in exposure to air as UV light breaks them down into harmless compounds (Nation Pesticide Information Centre, 2014). Pyrethrum has also been shown to naturally degrade on the plant either in the field or in the cooking process of agricultural crops (Vettorazzi, 1979). These properties and the natural source of the insecticide has allowed the certification of Pyrethrum to be used in organic agriculture where it is one of the most common non-synthetic insecticide used in this sector (European Commission, 2016).
Despite being labelled as an organic insecticide, the insecticidal properties of pyrethrin’s are not species specific. Therefore, as the pyrethrin’s are highly toxic, there application can have potentially harmful and toxic effects on beneficial insects, with a dose as low as 0.02 micrograms being sufficient enough to kill a bee (Caldwell et al.
2001, Cox 2002). Contrastingly, mammalian species have a low toxicity to pyrethrin’s, with high LD50 levels for rats and mice, as the toxins are metabolized therefore deactivated quickly within the mammalians hepatic system (Fishel, 2005)The low mammalian toxicity of pyrethrin’s along with Biodegradable nature of the compounds have meant that Pyrethrin’s are some of safest insecticides in use (Fishel, 2005).Insects small size and high nerve sensitivity makes Pyrethrin’s highly toxic and therefore an effective insecticide (Bradberry et al.
2005), successfully reducing the populations of insect pests that affect humans within homes, on pets or in commercial agricultural systems. This has allowed humans to control populations such as ants and spiders along with potentially disease carrying insects such as ticks and mosquitoes. This natural product has been further put to good use by being used as a base for the synthesis of synthetic pyrethroid insecticides which have proved to be more effective at insect population control.
Butdespite being less effective, the continued basic use of crushed Chrysanthemums’ throughout the centuries as an insecticide is due to its simplicity and natural source, which has gained the approval of both farmers and home owners as a more sustainable alternative to synthetic insecticides in the control of insect pests.
