Piperonyl butoxide, or PBO as it is most often called, is a pesticide synergist. A synergist is another chemical that is added to a pesticide product, in addition to the active and inert ingredients, to increase the potency of the active ingredient. Development of insecticide resistance has been a challenging problem for unlimited time and new solutions are yet to emerge. The use of synergist with the insecticide is thought to play a key role in reducing the resistance levels. The availability of a synergist was important because there were limited supplies of Pyrethroid available. Present study demonstrates the efficacy of PBO with pyrethroid insecticides available for controlling Spodoptera sp. Generally the 4^th instar larvae from 4 agriculture region were collected; bioassay technique and toxicity lines were achieved. Data obtaind showed that PBO were mostly effective to synergy any of those insecticides tested in all regions except for esfenvalerate and α -cypermethrin in Fayoum and fenvalerate in Sharkia. Evenly all insecticide were 99% suppressed in resistance levels except for α -cypermethrin in Fayoum was 80%. This suggests that when Organophosphorus appears to be not effective rapidly and the pest becomes highly resistance the use of pyrethroids always then needed. Subsequently when the pest developed resistance towards pyrethroids then piperonyle butoxide may have stop pyrethroid resistance when it happened. But when piperonyl butoxide becomes ineffective, we can try to use OP's compounds again.