Re: Malathion mode of action (was: Hmmmmmm (also Neps and Scale))

Carl Gustafson (
Tue, 14 Feb 1995 08:01:07 -0500

>Hmmmm I thought that malathion was more for spraying things and were
>not as effective for scale/mealy-bugs because both have a waxy coating
>that prevented them being wetted and hence picking up the poison. I
>think the actual toxin is the same, or at least the same family - i.e.
>anticholinesterase. From what I understand of biology (not much)
>cholinesterase is the stuff used to transfer nerve impulses from one
>nerve cell to the next, the poison in rogor/malathion/di-systron
>interferes with this so it acts like a "nerve gas"

Actually, it acetylcholine that does is responsible for transferring the
nerve signals. Cholinesterase breaks down the acetylcholine after it has
done it's job. Many organophosphorous compounds interfere with
cholinesterase activity, resulting in the nerves being in a constant state
of firing, so effectively preventing signals from getting through.

Since insects have different biochemistry than mammals, it is possible to
design compounds that have minimal effect on us, and maximal effect on
them. Malathion is in this class. And yes, these are basically nerve gas

There are basically two modes of action, of which the specifics I no longer
recall. However one is moderated by nicotine-like compounds, the other by
atropine, I think.

I did a fair amount of reading on this in my days as a chemist (I worked
for Stauffer Chemicals, managed into the ground by an inept executive
committee, IMO, and now gone), and my father worked on nerve gas antidotes
during a stint in the US Army in the early '50s, so I learned some from
him, too.


Carl Gustafson

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