Can I use plants to control insects?

In a healthy natural woodland where there is little direct human intervention, pest and disease organisms will always be present, but, unless there is a drastic environmental change, will normally kept in a state of equilibrium where they are not able to get out of hand to a level which is detrimental to the overall woodland community. This is the model for which the sensitive organic gardener will strive, but at the same time it is wise to recognise that there will often be some degree of intervention needed to manipulate the natural checks and balances to the gardener's favour, particularly if growing plants for food or ornament which would not normally occur in natural situations. Therefore biological control is about developing a range of techniques that use living organisms to maintain the beneficial equilibria in garden landscapes without causing adverse effects to humans or the wider environment. Of course, introducing exotic insects into any ecosystem entails taking risks of moving further from the intended equilibrium through unexpected interactions.