Butacide^® 8EC contains 8 pounds of the insecticide synergist piperonyl butoxide (PB) per gallon. The mode of action of PB is to interfere with mixed function oxidase (mfo) enzymes that insects possess and use to metabolize insecticides. One of the major mechanisms by which insects develop resistance to insecticides is increased mfo-mediated degradation of the toxicant. Butacide 8EC can counteract this resistance mechanism and prevent or delay the development of resistance. Field trials have been conducted on a worldwide basis to determine the role that Butacide 8EC may play in managing Heliothis resistance to pyrethroids. The results of these tests generally show that Butacide 8EC improved the activity of pyrethroids towards pyrethroid-resistant H. virescens in the USA and South America and H. amigera in Australia.