Large narcissus fly
Peter Taggart (Sat, 26 Oct 2013 13:45:00 PDT)

I believe that the soap forms a bubble which blocks the insects spiracles,
- air holes, thus suffocating it. When a plant is thoroughly wetted with
soapy water, or suds, most insect infestations seem to perish. I don't
believe that the plant would need to be submerged for very long!
I have flushed grubs out of bulbs with a jet of water.
Peter (UK)

On Sat, Oct 26, 2013 at 7:07 PM, Leo A. Martin <leo@possi.org> wrote:

I haven't had this pest, but a dense mealybug infestation in fine-spined
cactus can be
dealt with by submerging the entire plant in soapy water for a day or two,
then draining
and allowing to dry. The insects drown. The soap is necessary to wet the
waxy coat on
most insects.