DEVELOPMENT OF A TECHNIQUE TO MONITOR RESISTANCE TO BIODEGRADABLE INSECTICIDES IN-FIELD POPULATIONS OF TOBACCO BUDWORM (LEPIDOPTERA, NOCTUIDAE)

A procedure involving the use of glass vials containing insecticide wa s developed to monitor for resistance to biodegradable insecticides am ong field populations of adult tobacco budworms, Heliothis virescens ( F.). These insecticides are replacing pyrethroids for the tobacco budw orm control in areas where pyethroid resistance is a problem. Residues of profenofos, chlorpyrifos, methomyl, and endosulfan in glass vials were depleted in 2 d when they were held either in daylight or in the dark at room temperature. Residues of these compounds remained much lo nger (>70 d) in vials held in the freezer. The loss of toxicity was sh own to be mainly caused by hydrolytic degradation of the insecticide r ather than to the volatilization. The addition of mineral oil or ethyl ene glycol did not increase the persistence of insecticide residues in glass vials; however, addition of an organic acid (benzoic or decanoi c) to the vials significantly extended stability of insecticide residu es. Based on these results, treating vials with combinations of insect icides plus benzoic acid and storing them in a freezer is the preferre d technique if they are held for extended periods before use. The usef ulness of this technique was confirmed by gas-liquid chromatographic a nalysis of insecticide residues and by field monitoring data.