Studies on the Toxicity of Three Organic Phosphates Insecticide to Xenopsylla cheopis

Objective To study the toxicity of chlorpyrifos,phoxim and dichlorvos to Xenospylly cheopis in laboratory.Methods The residual smearing method was used.Results (1) The LC_(50) of chlorpyrifos phoxim and dichlorvos to(X.cheopis) were(5.961 5 mg/L),(6.787 3 mg/L) and(7.834 3 mg/L),respectively.(2) At the concentration of 100 and(200 mg/L),the KT_(50) values of dichlorvos were(9.0 min) and(4.2) min and after treated for 24 hours both death rates were 100%,the KT_(50) values of phoxim were(44.5) min and(23.6) min,the 24 hours death rates were(98.7%) and(97.8%),while the death rates for chlorpyrifos tyeated 24 hours were(98.9%) and 100%.(3) When at the concentration of 100 and(200 mg/L),after 18 min the knock down rates of dichlorvos were(94.5%) and 100%,17 min treated the knock down rates of phoxim were(24.4%) and(41.1%).(4) At the concentration of 50,100 and(200 mg/L),the 24 hours death rates for 30 days residue effect of phoxim were 0,but for dichlorvos were 0,(16.7%) and(31.0%).For chlorpyrifos at the concentration of 400,800 and (1 600 mg/L),after 24 hours the death rates for 210 days were(55.2%),(75.0%) and(96.4%).Conclusion The quick toxitocy of the three insecticides to(X.cheopis) is dichlorvosphoximchlorpyrifos.The residue effects are low.