Occurrence of aphids in peanut-cotton intercropping fields and evaluation of the resistance level to neonicotinoid insecticides
[Aims]This study aims to clarify the occurrence situation of aphids in peanut-cotton intercropping fields,evaluate the resistance level to 4 neonicotinoid insecticides of imidacloprid,thiamethoxam,clothianidin and dinotefuran,and guide to use insecticides rationally in this cropping pattern.[Methods]The population of Aphis craccivora Koch and Aphis gossypii Glover was assessed through visual observation in peanut-cotton intercropping fields.The resistance levels of field population and susceptible strains of A.craccivora and A.gossypii to the four neonicotinoid insecticides were determined by leaf dipping method.The toxicity of the four insecticides to larvae and adults of Propylaea japonica Thunberg was determined through spraying method.[Results]The occurrence of A.gossypii was more severe than that of A.craccivora.There were two peak periods in the occurrence of A.gossypii,the periods of seeding aphid and summer-type aphid,while there was one peak period in the occurrence of A.craccivora,which was close to the period of seedling aphid of the occurrence of A.gossypii.Field population of A.craccivora in Linqing were susceptible,susceptible,low resistant and susceptible to imidacloprid,thiamethoxam,clothianidin and dinotefuran respectively,with the resistance ratio(RR)of 3.89,1.58,6.55 and 1.46.However,the RR of A.gossypii field population in Linqing were 105.56,29.57,117.33 and 7.99 to imidacloprid,thiamethoxam,clothianidin and dinotefuran,exhibiting high level,moderate level,high level and low level of resistance,respectively.The selective toxicity ratio(STR)of the P.japonica and A.craccivora in the four insecticides was greater than 1,showing a positive selection.The STR of P.japonica and A.gossypii in imidacloprid and clothianidin and the STR of the larvae of P.japonica and A.gossypii in thiamethoxam was all less than 1.Only dinotefuran exhibited positive selectivity in P.japonica and A.gossypii.[Conclusions]Dinotefuran can be used to control aphids in peanut-cotton intercropping field during mid to late May.At the same time,other types of insecticides with high safety to natural enemies should be used alternately to slow down the increase of resistance to neonicotinoid insecticides.
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