A technique was developed to test the ability of oil spray diluents to penetrate the body wall of adult boll weevils. The dye, Calgo Oil Red N-1700^®; was used as an indicator that the oil treatments had penetrated the insect's cuticle. The technique consists of (1) applying the oil plus dye to the boll weevil by a dipping process, (2) washing the boll weevil in acetone several times to remove the dye from the outer surface of its body and (3) crushing the weevil using paper chromatography to determine if dye had penetrated the body wall. Most of the tested diluents had excellent penetrating effects. The malathion ulv, which is the technical material and an oil, had a 50% penetration ability. In combination with cottonseed oil and paraffinic oils it had a range of 92 to 100% penetration. Additionally a difference was observed in the penetration properties of different production batches of once refined cottonseed oil.