Control of Aphis fabae on broad beans (Vicia faba) by the systemic action of gamma-bhc,thionazin and aldicarb

The in-row application of aldicarb granules at 2 lb active ingredient (a.i.)/acre (2·24 kg/ha) at sowing gave complete control of Aphis fabae Scop. on broad beans (Vicia faba L. cv. Seville) up to 7 days before harvest and resulted in a three-fold increase in yield compared with a similar thionazin treatment. Bean plants grown from seeds which were soaked in a gamma-BHC solution at 20 ppm for 24 h prior to planting were protected from this aphid for most of the growing season almost as effectively as with the thionazin treatment. A thin-layer chromatography method was developed for the determination in plants and soil of aldicarb and its two major toxic metabolites, the sulphoxide and sulphone. Gas-liquid chromatography was used to monitor the declining levels of gamma-BHC and thionazin, and simultaneous bioassays were made with Aphis fabae on excised leaf discs from the crop. Analysis of the bean seeds and pods at harvest 90 days after sowing indicated no detectable gamma-BHC, less than 0·01 ppm of thionazin and approximately 0·09 ppm total residue of aldicarb sulphone and sulphoxide. Approximately 22% and 13% of the applied aldicarb, in the form of sulphone and sulphoxide but not the parent compound, remained in the top 6 in (152 mm) of soil at the end of 2 and 4 months respectively. Toxicity studies with Aphis fabae, Acyrthosiphon pisum Harris, and Megoura viciae Buck showed an increasing sensitivity in that order to gamma-BHC at 1 ppm in bean plants. Acute toxicity investigations with feeding Aphis fabae indicated an increasing sensitivity in the order of gamma-BHC < aldicarb sulphone < aldicarb sulphoxide < thionazin < aldicarb. Despite the high acute toxicity of thionazin to Aphis fabae it gave low protection against aphids, possibly owing to its relatively short persistence in both plants and soil when compared with aldicarb.