...it is also worth mentioning that soap by itself is toxic to many pests, spider mites in particular come to mind, so adding a couple drops of soap helps you in 2 ways.

...i actually remember reading a DIY mite treatment that called for a cup of vegetable oil mixed with a tablespoon of dish detergent, you then took this and used it as a base, meaning you'd take say a teaspoon of this mixture and dilute it down and then use it to spray for mites.

...anyway, i digress.

peace, SOG