PYRETHRUM

What is Pyrethrum?

Pyrethrum is a highly effective insecticide which both kills and repels insects.   Pyrethrum is a natural plant oil extracted from the flowers of the chrysanthemum daisy (chrysanthemum cinerariaefolium).   The majority of the pyrethrum produced in the world comes from the African countries of Kenya, Tanzania, Rwanda and Ecuador.  Other countries such as Australia, Japan, Brazil and others produce smaller amounts.  Pyrethrum is an ancient insecticide. The insecticide properties of the flowers were documented in the early 1800’s but it is suspected that the flowers were used to kill insects a considerable time earlier. The first commercially available products were powders made from ground flowers and later crude oil extractions became popular. Mature pyrethrum flowers are picked by hand, sun dried to remove moisture, and sent to a processing plantor extraction of crude pyrethrum. Crude pyrethrum contains 30 to 35 percent pyrethrins (insecticide) and about 50 percent impurities.  Pyrethrins are contact insecticides which affect the insect's nervous system.  Today, the refining of crude pyrethrum extract to remove the plant material, waxes, etc. is a highly complex process resulting in a product that is clear and free of allergens.  On the EPA Green List, Pyrethum is one of the least toxic insecticides to mammals.  Pyrethrum is biodegradable and breaks down quickly in sunlight, air and water.

Pyrethrum and Piperonyl Butoxide:

Despite its safety and effectiveness, natural pyrethrum does have certain limitations.  Pyrethrum is relatively expensive due to the costs of harvesting chrysanthemum flowers (containing pyrethrum) by hand.  Also, various insects such as the common housefly can detoxify and recover from small amounts of pyrethrum.  Natural pyrethrum alone tends to break down quickly in the environment, rapidly losing effectiveness after outdoor application.  Research has overcome the detoxification issue by combining pyrethrums with piperonyl butoxide (PBO), a liquid synergist.  PBO works by restricting an enzyme that insects use to detoxify pyrethrum, allowing the insecticide to be more effective.

Safety

Pyrethrum's qualities of rapid degradation have also turned out to be a blessing in disguise.  Because it is biodegradable, Pyrethrum has been EPA registered and USDA accepted for use in food processing facilities.  Pyrethrum is also applied to fruits and vegetables like tomatoes post harvest on the way to market.  Even though pyrethrins are nerve poisons, they are not cholinesterase inhibitors like organophosphate or carbamate insecticides.  Pyrethrins are low in toxicity to mammals because they are quickly broken down into inactive forms and pass from the body in the urine and feces.

	Chrysanthemum Fields

Knockdown Effects

Pyrethrum has been trusted for decades in both household and agricultural applications.  New research has found that pyrethrum, combined with a synergist, is one of the fastest-acting insecticides available.  Pyrethrum knocks down and paralyzes insects before it kills.  Upon exposure to pyrethrum, insects are thrown into a state of nervous disorder and run or fly around erratically.  Hidden insects are flushed from their hiding places and scuttle about until they contact lethal amounts of pyrethrum.  This response is due to the fact that the insect has lost control of its central nervous system.   These effects are collectively referred to as activation. 

Jamming

Recent research has discovered that Pyrethrum has a "jamming" effect on insects prior to activation.  Tests have shown that the biting female mosquito's food searching mechanism, or "black box", can be jammed by trace amounts of pyrethrum.  An example test of the "jamming" phenomenon would be to fill glass cage full of female mosquitoes and find some brave volunteers.  Those who place their arms into the cage can expect to receive up to 50 bites per minute. Next, expose the mosquitoes to trace amounts of pyrethrum.  Then, those who place their arms into the cage receive no bites even though the mosquitoes otherwise seem normal.

Resistance

There is another advantage to using pyrethrum.  The reason is not fully understood, but insects do not become resistant to the natural insecticide.  After decades of successful use, no insect population has ever developed significant pyrethrum resistance.  Intense study of the pyrethrum molecule has led to the production of synthetic pyrethroid insecticides.  But, science has not yet devised a synthetic insecticide that combines the speed, effectiveness, activation effects and biodegradability of natural pyrethrum.