In article ,
Martin wrote:
On Fri, 15 Aug 2014 22:54:08 +0100, Sacha wrote:
On 2014-08-15 19:31:45 +0000, David Hill said:

Ah, no, that's not what they had done. Mosquito larvae hang from
the surface of stagnant water, which is why draining the Fens
eliminated marsh ague a century or two back. The usual method
of preventing that is to put a small amount of oil in, and that
kills the larvae. Paraffin is cheap and not very volatile, so
is safe, but it does stink when it evaporates (e.g. on a hot day).

You can also use detergent, but that usually needs a LOT more and
taints the water worse.

I've found that if you give a quick spray with an aerosol fly spray
over the surface it kills off the mosquito larvae and doesn't leave any
deposit on the water surface.

Well, yes and no. It depends on what is in the spray how much
residue it leaves and whether it is more toxic than a larger
amount of paraffin. Also, paraffin has a preventative effect
and is feasible for large areas, like sizeable ponds.

Olive oil works too.

Any oil does. However, using olive oil for large areas is very
expensive. Paraffin is cheap, and will eventually biodegrade.


Regards,
Nick Maclaren.