An adult vial test (AVT) was developed to monitor for resistance to organophosphate (OP), carbamate and cyclodiene insecticides in the tobacco budworm, Heliothis virescens (F). Laboratory data showed that toxicity of OP (chlorpyrifos, profenofos), carbamate (methomyl) and cyclodiene (endosulfan) insecticides disappeared in glass vials between 2 to 4 days at room temperature, but remained up to 60 days in vials held in the freezer. The loss of toxicity in the vials was shown to be due to hydrolysis rather than to volatilization. Adding an organic acid such as benzoic or decanoic to the vials greatly increased residue life. The usefulness of this technique for resistance monitoring was confirmed by field data from Texas, Arkansas, Mississippi and Louisiana in 1992. Field monitoring data indicate that resistance to organophosphate, carbamate and cyclodiene insecticides is present in many tobacco budworm populations.