Pyrethrins & Pyrethroids
Botanical vs Laboratory Synthesized
|The six esters known collectively as pyrethrins are produced in the Chrysanthemum plant, Chrysanthemum cinerariaefolium. Pyrethrins are found at particularly high concentration within flower structures known as achenes which are located in the flowerhead of the Chrysanthemum. The extract from the Chrysanthemum plant containing pyrethrins is called pyrethrum.
Pyrethroids are synthetic, or man-made, versions of pyrethrins. There are two major classes of pyrethroids, Type I and Type II pyrethroids. Type I pyrethroids are characterized by their ability to knockdown insects quickly but the Type II pyrethroids will induce higher insect mortality than Type I pyrethroids. While pyrethrum extract is composed of 6 esters which are insecticidal, a synthetic pyrethroid is composed of only one chemically active compound.
One result of the similarities between the chemistry of pyrethrins and synthetic pyrethroids is that have a similar mode of action (i.e. both pyrethrins and pyrethroids induce a toxic effect within the insect by acting on sodium channels; see Mode of Action). Some differences in the chemistry between pyrethrins and synthetic pyrethroids have the result that synthetic pyrethroids have relatively longer environmental persistence than do pyrethrins. Pyrethrins have shorter environmental persistence than synthetic pyrethroids because their chemical structure is more susceptible to the presence of UV light and changes in pH.
One important difference between pyrethrins and synthetic pyrethroids is the behavioral effect they have on insects. Pyrethrins have a unique ability to induce excitation behavior in the target insect. This excitation behavior is characterized by erratic and increased movement by insects. This is sometimes referred to as ‘flushing’ action. This flushing action induced by pyrethrins is highly desirable; because of the increase in movement, it often results in increased insect exposure to pyrethrins.
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