"wendy7" wrote in message news:%ZToc.29105$fE.24424@fed1read02...
Good advice Nick, but please could you explain your quote:-

"Pyrethrins can often be rendered useless by a single mutation in the
insects' voltage-gated sodium channel gene".

Thanks,
--
Cheers Wendy


Voltage-gated sodium channels are proteins that sit in cell membranes
and form pores whick allow sodium ions to flow through. The flow of
sodium ions changes the electrical potential of the membrane, and in
neurons, sodium channels are required for propagation of electrical
signals. Pyrethroid pesticides act by blocking the sodium channels in
the insects' neurons. Basically, they shut down the insects' nervous
system.

But since the interaction between sodium channel and pyrethroid is so
precise, it can easily be disrupted. There are a whole host of simple
mutations that change the shape of the sodium channel sufficiently to
prevent pyrethroid binding while still allowing the protein to
function as a sodium channel. Just one or a few DNA base pair changes
is all that is required.

Other sodium channel blockers include tetrodotoxin, which is the toxin
that makes eating Fugu (puffer fish) in a Japanses restaurant so ...
exciting. The major sodium channels in our own neurons are blocked by
tetrodotoxin. I read somewhere that good Fugu contains just enough
tetrodotoxin to make your lips tingle!

Anway, getting back to insects, the result of all this is that
resistance is more likely to occur with a pesiticide that has a single
mode of action that can be blocked by a single nucleotide substitution
than with something like soap or oil that simply smothers the insects.

If you are interested in learning more, a google search using the
terms "knockdown resistance" and "sodium channel" will probably give
you more information than you could possibly want.

regards,
Nick