It's a long time since we discussed this, but given the impending withdrawal of permethrin, readers might be interested in some info I've dug up recently on pyrethrum.
So, it's "one of the safest and most widely used natural pesticides in the world... Pyrethrins (the active chemicals in the powder) are incredibly potent neurotoxins - just not to humans... We now know how pyrethrum works as an insecticide: pyrethrins bind to important protein passageways (voltage-gated sodium channels) for sodium ions in nerve cells. When pyrethrins bind to these proteins, the nerve cells wildly overfire, causing involuntary muscle contractions, paralysis and even death. This physiological reaction sounds bad, and it is indeed problematic for invertebrates like insects, molluscs, arachnids, and some vertebrates, like fish. But natural pyrethrins are not very toxic to other vertebrates, like humans and birds."
Hence we can use it safely on chickens; humans and birds.
"... A single ancient change in the DNA of insects makes their nerve cells a hundred times more sensitive to pyrethrins than ours. By contrast, cats and fish are sensitive to pyrethrins because they lack one of the liver enzymes we humans use to detoxify pyrethrins." So the cat owners amongst us might want to note, if they didn't know it already, that using pyrethrum may present a risk to their feline friend(s).
Source: N Whiteman Most delicious poison 2023:15-17.
Had to take a couple of snaps with the phone.
