Piperonyl butoxide (PBO) is a man-made pesticide synergist and adjuvant. It makes insecticides, both for use in plant applications and commercial pesticide applications, more effective. PBO works by preventing insects from being able to break down insecticide active ingredients. Insects have enzymes in their bodies that break down some insecticides. PBO stops some of these enzymes and allows insecticides more time to work.