In 1992 and 1993, young adult boll weevils were released onto diflubenzuron (Dimilin® = DFB) treated and untreated cotton plants grown in twenty 3' x 3' x 5' screened field cages. Seven days later weevils were recovered and several parameters were measured. DFB significantly reduced hatch, flight ability, and cuticle hardness in both years; survival apparently was reduced in 1992, but not in 1993. Mating ability was unaffected in either year. The combination of reduced hatch, flight ability, hardness, and possibly survival, along with the late season persistence of DFB may help to explain its effectiveness.