Substances that may damage insects above the soil also have the potential to damage beneficial organisms in the soil.  Such remedies may treat the plant at the expense of the ecosystem.  The potential effects these remedies may have on beneficial organisms above and in the soil have been noted.  Most garden vegetable plants lasts for a year, whereas the soil takes years to build into a healthy medium.  If one year you drive out beneficial organisms in order to get rid of a pest problem and harm the soil in the process, the following year there is a distinct possibility that your garden will have even more problems and require even more remedial measures.  This could very well become a vicious cycle.  Although there may be times you want to use these remedies to save some plant, do so with the consideration for the soil.  We do have organic choices as backyard gardeners.  Just remember, The soil is living!