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Cassie Krejci is right. There are a lot of py-words out there to break down: pyrethrum, pyrethrins, permethrin, pyrethroids. She shares the differences and helps clear up possible confusion.
Source: MGK.com. Link.
Pyrethrins are broad spectrum and kill a wide variety of insects, while pyrethroids tend to have longer residual effects and increased stability in storage.