Abstract: 【Aim】 The toxicity of pyrethroid insecticides can be synergized by organophosphates and carbamates through inhibition of insect carboxylesterase (CarE) activity. This study aims to assess the synergism of 13 organophosphate and carbamate insecticides, and four synergists to beta-cypermethrin for the control of wheat aphids. 【Methods】 The I₅₀ values of 13 insecticides and two inhibitors to the CarE activities in Sitobion avenae and Rhopalosiphum padi wingless adults were determined by using the method of in vitro inhibition. The method of the residual film in glass tube was used to determine the toxicity of each insecticide and its mixture with beta-cypermethrin (3∶1) to both wheat aphid species. Co-toxicity coefficient (CTC) was used to evaluate the synergism. 【Results】 Except for thiodicarb, the other 12 insecticides showed significantly higher inhibiting effect on S. avenae than on R. padi. Dichlorvos mixed with beta-cypermethrin was the strongest inhibitor to the CarE activities of S. avenae and R. padi, with the I₅₀ values of (5.40±0.74)×10^-8 mol/L and (1.41±0.41)×10^-5 mol/L, respectively. The joint-toxicity test of pirimicarb, methomyl, carbosulfan, carbaryl, triazophos, profenofos, malathion, dichlorvos, DEF and TPP respectively mixed with beta-cypermethrin showed that except for profenofos, all the other nine chemicals enhanced the toxicity of beta-cypermethrin to R. padi significantly. And malathion showed the strongest synergistic effect (CTC=467.59); and except for methomyl, profenofos and malathion, the other seven chemicals showed significant synergism to beta-cypermethrin against S. avenae with the CTC range from 146.87 to 626.30, of which the triazophos showed the highest CTC value (626.30). 【Conclusion】 We identified a number of insecticides or synergists with higher toxicity against S. avenae and R. padi when used in combination with beta-cypermethrin, which include pirimicarb, carbosulfan, triazophos, dichlorvos, DEF and TPP. These results provide scientific basis for the effective control of wheat aphids in wheat production.

Key words: Sitobion avenae, Rhopalosiphum padi, carboxylesterase, synergism, co-toxicity coefficient (CTC), beta-cypermethrin