Tanacetum cinerariifolium, widely recognized as Dalmatian pyrethrum or pyrethrum daisy, is a plant of significant importance in natural insect control. For centuries, its dried flowers have been utilized for their unique insecticidal properties. It is renowned globally for producing natural compounds that effectively deter and eliminate various insect pests. Its long history underscores its enduring value as a natural solution for managing insect populations.
Understanding Tanacetum Cinerariifolium
This perennial plant features striking daisy-like flowers with white petals and a yellow center. Its foliage is blue-green, and the plant can reach a height of 45 to 100 centimeters. Tanacetum cinerariifolium originated from the Dalmatia region of Croatia, located along the eastern Adriatic coast, including areas of Bosnia, Herzegovina, and Montenegro.
From its native habitat, the plant’s cultivation spread globally, with commercial farming beginning in the 19th century. Its introduction to Kenya in 1928 marked a turning point, and it is now also cultivated in other regions such as Australia, Tanzania, Rwanda, Ecuador, France, and Chile. The plant’s insecticidal qualities stem from natural compounds called pyrethrins, which are concentrated primarily within its flower heads, specifically in the tiny oil glands of the achenes or seed cases. The highest concentration of these compounds is found when the flowers are in full bloom, particularly within the yellow disc florets.
How Pyrethrins Act as Insecticides
Pyrethrins exert their insecticidal effect by acting as neurotoxins, targeting the insect nervous system. These compounds bind to voltage-gated sodium channels in insect nerve cells. Upon binding, pyrethrins prolong the open state of these channels, allowing an uncontrolled influx of sodium ions. This influx depolarizes the nerve membrane, disrupting electrical signaling.
This disruption leads to hyperexcitability of nerve cells, causing continuous electrical signals throughout the insect’s body. This hyperactivity manifests as tremors and convulsions, rapidly progressing to paralysis, often referred to as the “knockdown effect.” Ultimately, the insect’s nervous system is overwhelmed, leading to death. Pyrethrins can also interfere with other ion channels, such as calcium channels, and inhibit metabolic enzymes like ATPases, contributing to the insect’s demise.
Applications and Safety Considerations
Pyrethrin-based products are used across various sectors for their effective insecticidal properties. They are common ingredients in household insecticides, like sprays and aerosol bombs, and are used in pet treatments for fleas and ticks. In agriculture, these compounds protect crops like cotton, wheat, maize, and alfalfa from pest infestations. Pyrethrins also play a role in public health initiatives, in mosquito control programs, applied to treated bed nets and clothing to prevent insect-borne diseases.
Pyrethrins are generally considered to have low toxicity for humans and mammals. Their bodies can rapidly metabolize and break down the compounds, preventing accumulation to harmful levels. Differences in the structure of sodium channels in mammals make pyrethrins less effective at binding to them. Environmentally, pyrethrins are biodegradable and quickly decompose in sunlight, which limits their persistence in the environment. However, their potential impact on non-target insects, including beneficial species like honey bees, and their toxicity to fish and other aquatic organisms if products enter water bodies through runoff should be noted.
Cultivation and Extraction
Cultivating Tanacetum cinerariifolium requires specific environmental conditions for optimal pyrethrin yield. The plant thrives in temperate climates with bright, direct sunlight, receiving at least six hours daily. Moderate temperatures are preferred for growth, with an optimal range of 20-25°C. Cool nights and warm days are conducive to higher pyrethrin content and optimal flowering.
The plant grows best in well-draining loam soil, though it can adapt to various soil types, provided they are not excessively rich. High annual rainfall (1000-1400 mm) supports its development, but a dry period of at least two months can also be beneficial. Harvesting of the flower heads occurs when about three-quarters of the disc flowers are open, as this stage corresponds to the highest concentration of pyrethrins. After harvesting, the flowers are dried and pulverized. The pyrethrins are then extracted using various methods, commonly involving solvents like ethanol, methanol, or acetone, to produce the active ingredient for commercial products. Supercritical CO2 extraction is another effective technique.