Viewpoint: Yes, introducing the natural enemies of invading foreign species is a safe and effective way to bring the invading species under control, as long as rigorous screening and proper release strategies are utilized.

Viewpoint: No, introducing the natural enemies of invading foreign species such as purple loosestrife is neither safe nor effective; as history shows, numerous such attempts have backfired.

Just as Sir Isaac Newton demonstrated that every action is accompanied by an equal and opposite reaction, many naturalists believe that for every pest problem there is an equal and opposite natural counterpart...