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. >