PBO(Piperonyl butoxide) is used as a component of pesticide formulations. It is a waxy white solid. It is a synergist. That is, despite having no pesticidal activity of its own, it enhances the potency of certain pesticides such as carbamates, pyrethrins, pyrethroids, and rotenone. PBO is mainly used in combination with insecticides, such as natural pyrethrins or synthetic pyrethroids, in ratios (PBO: pyrethrins) ranging from 3:1 to 20:1. It is suitable for pre-harvest and post-harvest application to a wide variety of crops and commodities, including grain, fruits and vegetables. The application rates are low; the highest single rate is 0.5 lbs PBO/acre. It is also used extensively as an ingredient with insecticides to control insect pests in and around the home, in food handling establishments such as restaurants as well as for human and veterinary applications against ectoparasites (head lice, ticks, fleas). A wide variety of water-based PBO-containing products such as crack and crevice sprays, total release foggers, and flying insect sprays are produced for home use. PBO has an important public health role as a synergist used in pyrethrins and pyrethroid formulations used for mosquito control (e.g. space sprays, surface sprays and bed nets). Because of its limited, if any, insecticidal properties, PBO is never used alone.