What’s the difference between pyrethrins and pyrethroids? And is pyrethrum the same as these things? What’s with all the py-words?!

Pyrethrum and pyrethrins are insecticide extracts from blossoms of certain species of chrysanthemum. Pyrethrum is the crude extract from the flower heads, whereas pyrethrins are the active ingredients found in those flower heads. Pyrethrins contain six active molecules (esters) that act as the killing agent: Pyrethrins I & II, Jasmolin I & II and Cinerin I & II.

Pyrethroids, on the other hand, are synthetic versions of pyrethrins. They have fewer chemical variants and usually only contain one molecule that mimics a single ester. Because pyrethroid
molecules are made the same way every time, with such few variations, it is thought that insects can become resistant to pyrethroids more quickly than they would to pyrethrins.

The concentration of pyrethrins varies depending on when the flowers were harvested and the environmental conditions (rainfall, temperature, etc.) in which they were grown. The pyrethrins affect the insect’s nervous system with a slightly different ratio of these molecules each time, making it theoretically more difficult for the insect to develop resistance. It’s similar to how coffee tastes differently based on the beans’ environmental conditions and where they were grown. It doesn’t matter if the other parts of the coffee recipe were the same, the coffee will “affect” our tastebuds differently based on these characteristics of the beans.

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