April 2004 Permethrin - A Manmade Mimic of a Natural Pesticide Permethrin is one of the many chemical pesticides known as synthetic pyrethroids that have their chemical roots in the natural botanical pesticide called pyrethrum. Pyrethrum is extracted from the pyrethrum daisy, Tanacetum cinerariaefloium, a member of the chrysanthemum family. The pyrethrum daisy, a white flower with a yellow center, has evolved a unique chemistry. Within its flowerhead are oil glands that produce six esters known as pyrethrins, that, in combination, work to deter and kill insects. Pyrethrum is thought to be the oldest pesticide known to man. Pyrethrum is native to China and was introduced into Europe and the Middle East when trade occurred along the silk routes in ancient times. The flowers were ground to a powder and used on all types of pests from head and body lice to fleas, flies, and mosquitoes. Pyrethrum was used on a large scale by armies, from the time of the Napoleonic wars up to World War II when synthetic pyrethroids were developed and took the place of pyrethrum.
Over 1,000 synthetic analogs to pyrethrum have been developed, but only about a dozen are used as pesticides in the U.S., with permethrin being the most commonly used. Over the past 30 years scientists have been able to manipulate the chemistry of the natural pyrethrins to improve their biological activity by improving their stability when applied into the natural environment. The improved stability of synthetic pyrethroids allows for their use on trees, crops, and lawns as well as for human and animal pests. This extended stability provides greater effectiveness than natural pyrethroids, at less cost.
The environmental fate of pyrethroids is also a positive aspect of these pesticides. They breakdown when exposed to moisture and UV radiation (sunlight), they breakdown (hydrolysis) when released into an alkaline environment (limestone or shell soils), and pyrethroids bind tightly to soil particles where they are broken down microbially. The ability of pyrethroids to bind tightly to soil or fabrics provides other benefits. By binding to soil particles, if there is a spill, it can easily be cleaned up by removal of the soil, and being practically insoluble in water, it is unlikely to leach into groundwater. Also, because of this extremely tight binding ability (adsorption), pyrethroids can be applied to fabrics and maintain repellent and insecticidal capabilities for several weeks and several detergent washings. Pyrethroid treated clothing and bednets are used extensively by the U.S. military to provide protection in fly, mosquito, flea or tick infested areas.
Permethrin is the synthetic pyrethroid we use at South Walton County Mosquito Control for our mosquito adulticiding program. The trade name of the formulation we use is Biomist 4+4, received as a bulk shipment, ready to use. It consists of 4% permethrin, 4% piperonyl butoxide (PBO) a synergist to increase the potency of the permethrin, and 92% light mineral oil - the carrier for the pesticide. None of the additives in permethrin formulations have been shown to affect human health or the environment. The product label for Biomist allows a dose rate of 4.5 ozs. to 18 ozs. per minute at 10 mph, we apply it at 6.5 ozs. per minute at 10 mph from our spray trucks, with excellent results. The advantages with Biomist 4+4 are; we don’t have to formulate it - it’s ready to use, it is practically odorless, it has no damaging effect on paint or equipment, has a quick knockdown of mosquitoes, and most importantly it has little if any toxicity to man, other mammals, birds, or plants. Acute toxicity in humans, through occupational exposure, has caused skin sensations such as itching, burning, and numbness that usually subsides within 24 hours. No chronic effects have been reported in humans and permethrin is not classified as an agent which causes cancer, genetic damage or birth defects, and does not affect fertility, reproduction or the development of offspring.
Permethrin controls a wide range of insects by contact and stomach poison activity. Permethrin acts as a repellent to insects but also causes death by paralyzing their nervous system. Permethrin is highly toxic to insects, fish, and many aquatic invertebrates, particularly insects and crustaceans. For this reason, the product label for Biomist 4+4, prohibits use within 100 feet of aquatic ecosystems.
When used as directed, Biomist 4+4 is safe to the applicator, safe to the environment, safe on our equipment, and extremely effective against adult mosquitoes. As with all pesticides, good stewardship of their application must be practiced. After several years of using pyrethroids as an adulticide we will need to switch to another class of pesticides (organophosphates - i.e. malathion) to avoid genetic resistance in our targeted pest, the mosquito. |