The toxicity of some benzimidazole fungicides to the pea aphid, Acyrthosiphon pisum

SUMMARY Field bean plants were treated with benomyl in a glasshouse and nymphs of Acyrthosiphon pisum were then caged on the second pinnate leaf. Soil drenches of 75 μg benomyl/ml or above increased mortality of the aphid. The concentration of methyl benzimidazole‐2–yl carbamate (MBC = carbendazim) in leaf sap, determined by a Penicillium expansum bioassay, was proportional to the concentration of benomyl applied as a soil drench or foliar spray, but lower in sprayed plants than drenched plants. The compound persisted at high concentrations in the second leaf for 4 wk but was present in low amounts in young leaves. Nymphs were also fed through membranes on artificial diets incorporating benzimidazole compounds. In this artificial system a commercial formulation of Carbendazim (Bavistin) increased aphid mortality whereas the formulation medium was inactive. Thiabendazole (as the commercial formulation Tecto 60), 2–aminobenzimidazole and benzimidazole were also inactive. It is suggested that the carbamate moiety of carbendazim causes the aphicidal activity of the compound.