【Objective】 In order to solve the problems of single types and reduced sensitivity of traditional insecticides for the control of Aphis citricola von der Goot on apple trees, the co-toxicity of abamectin and dinotefuran against Aphis citricola was measured, as well as the field experiment was carried out to verify the synergistic effection. Then, the application effect of the nanoparticles sustained-release formulation loading the above two chemical pesticides was evaluated by field experiments for ultimately obtaining the control plan for Aphis citricola. 【Methods】 Indoor bioassay was carried out by leaf dipping method. Experimental insects were gathered from apple trees in the greenhouse of Dongyang experimental Base, Shanxi agricultural university, which had not been treated with any pesticides. Four combinations of abamectin and dinotefuran were set up by the active ingredient ratios of 1:2, 1:4, 1:8, and 1:16. Firstly, fresh and tender leaves were immersed in the insecticide solutions for 5 seconds, and then moved back up into a petri dish covered with wet filter paper. Secondly, healthy adult aphids were chosen and placed to the leaves surface for incubation, the mortality were recorded after 24 hours of feeding. The co-toxicity of abamectin and dinotefuran to Aphid citricola was evaluated by Sun Yunpei's co-toxicity coefficient method. Based on the co-toxicity results, two field trials were conducted to evaluation the control effects in April and June 2021, in Yuncheng City, Shanxi Province. Five treatments were set up in each experiment. There were three different doses of the compound (abamectin 5% EC and dinotefuran 20% SG) and two single insecticide (abamectin 5% EC, dinotefuran 20% SG). The three doses were 4, 9, 13.5 mg·kg-1 on 1:2 ratio, respectively; as well as 15, 20, 22.5 mg·kg-1 on 1:4 ratio, respectively. Water was set up as control. Knapsack sprayer was used to evenly spray the apple tree with the amount of 2~3 L per tree. Each treatment had 4 replications, and there were 2 trees in each replication. The insect population number was investigated on the 3, 7, and 15 days after application. In addition, 2.25% abamectin ·dinotefuran co-delivery nanoparticles formulation (2.25% DACNPs) on the ratio of 1:4 was prepared and applied. The field experiment was carried out from May to June 2022 in Linyi County, Shanxi Province. Four treatments were designed for the experiment, including 2.25% DACNPs, the compound on a 1:4 ratio, and the addition of the additive GY-T1602 to the both respectively. It has been applied twice during the occurrence period of aphids and investigated the insect population on 7 and 15 days after each application. Finally, the population decline rates and the control effects were calculated. 【Results】 When the compound ratio of abamectin and dinotefuran were 1:2, 1:4, and 1:8, the co-toxicity coefficient (CTC) on Aphis citricola were respectively 251.61, 260.72 and 126.25. They were greater than 120, indicating that these ratios have synergistic effect on Aphis citricola. The LC50 of abamectin was 0.66 mg·L-1, while the dinotefuran was 106.44 mg·L-1. The LC50 of the combinations on the ratio of 1:2 and 1:4 were 0.75 and 1.28 mg·L-1, respectively. It showed that the combinations could enhance the toxicity of dinotefuran significantly. Field trials showed that, on the ratio 1:2, when the dosages were 4.5 and 9 mg·kg-1, the control effects against Aphis citricola on 7~15 days were only 51.69%~78.46%, significantly lower than those of single agent. At the dosage of 13.5 mg·kg-1, the control effect was comparable to dinotefuran alone, but still lower than that of abamectin, the difference among all of them were not significant. On the ratio of 1:4, the control effects on 3 days were 91.44%~99.63% at the dosages of 15, 20 and 22.5 mg·kg-1, that were equivalent or slightly higher than abamectin or dinotefuran alone. However, the combination could reduce the active constituent amount of abamectin or dinotefuran by the range of 10%~70%. Moreover, the control effect of 2.25% DACNPs against Aphis citricola on 7~15 days after the first applied was 41.44%~64.58%, that was lower than that of the 1:4 combination. After the secondary applied, the control effect of 2.25% DACNPs on 7~15 days was 79.80%~91.65%, which was equivalent to the 1:4 combination. The results indicate that the 2.25% DACNPs has sustainable efficacy on Aphis citricola. By adding adjuvant GY-T1602, compared with the same treatment without the addition, the control effects were all improved to a certain degree, there were significant difference on the 7 days after the first applied, but no significant difference on the other days. It indicates that adding adjuvant could improve the quick effect. 【Conclusion】 It is recommended to use 2.25% DACNPs in initial occurrence of Aphis citricola, however use the combination of abamectin and dinotefuran by the ratio of 1:4 in peak occurrence to reduce the insect population density quickly. Adding adjuvant GY-T1602 in the spray could obtain a higher efficacy, in particular in the early control effect.
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