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 was developed to monitor for resistance to biodegradable insecticides among field populations of adult tobacco budworms, Heliothis virescens (F.). These insecticides are replacing pyrethroids for the tobacco budworm 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 longer (>70 d) in vials held in the freezer. The loss of toxicity was shown to be mainly caused by hydrolytic degradation of the insecticide rather than to the volatilization. The addition of mineral oil or ethylene glycol did not increase the persistence of insecticide residues in glass vials; however, addition of an organic acid (benzoic or decanoic) to the vials significantly extended stability of insecticide residues. Based on these results, treating vials with combinations of insecticides plus benzoic acid and storing them in a freezer is the preferred technique if they are held for extended periods before use. The usefulness of this technique was confirmed by gas-liquid chromatographic analysis of insecticide residues and by field monitoring data.