Synergistic effect of slow-releasing nanocapsules containing abamectin and dinotefuran on the control against Aphis citricola

Abstract: 【Objective】In order to solve the problems of single type 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 A. citricola was examined, and the field experiment was carried out to verify the synergistic efficacy. Then, the application effect of the slow-releasing nanoparticles loading with the above two chemical pesticides was evaluated by field experiments for ultimately obtaining the control plan for A. 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 were not 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 leaf surface for incubation, and the mortality was recorded after 24 hours of feeding. The co-toxicity of abamec-tin and dinotefuran to A. citricola was evaluated by Sun Yunpei’s co-toxicity coefficient method. Based on the co-toxicity results, two field trials were conducted to evaluate 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 or dinotefuran 20% SG). The three doses were 4, 9 and 13.5 mg·kg-1 at 1∶2 ratio, respectively; as well as 15, 20 and 22.5 mg·kg-1 at 1∶4 ratio, respectively. Water was set up as the control. Knapsack sprayer was used to evenly spray the apple tree with the amount of 2-3 L solution per tree. Each treatment had 4 replications, and there were 2 trees in each replication. The insect population number was investigated on the 3rd, 7th and 15th day after application. In addition, 2.25% abamectin ·dinotefuran co-delivery nanoparticles formulation (2.25% DACNPs) at 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 at 1∶4 ratio, and the addition of the additive GY-T1602 to both, respectively. It was applied twice during the occurrence period of aphids and the insect population was investigated on 7th and 15th day after each application. Finally, the population decline rates and the control effects were calculated. 【Results】When the compound ratio of abamectin and dinotefuran were at 1∶2, 1∶4 and 1∶8, the co-toxicity coefficients (CTC) on A. citricola were 251.61, 260.72 and 126.25, respectively. They were greater than 120, indicating that these ratios had synergistic effect on A. 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 at 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, at the ratio of 1∶2, when the dosages were 4.5 and 9 mg · kg-1 , the control effects against A. citricola in 7-15 days were only 51.69%-78.46%, significantly lower than those of any 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, and the difference among all of them was not significant. At the ratio of 1∶4, the control effects in 3 days were 91.44%-99.63% at the dosages of 15, 20 and 22.5 mg · kg- 1 , which were equivalent to 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 A. citricola in 7-15 days after the first application was 41.44%-64.58%, which was lower than that of the 1∶4 combination. After the secondary application, the control effect of 2.25% DACNPs in 7-15 days was 79.80%- 91.65% , which was equivalent to the 1∶4 combination. The results also indicated that the 2.25% DACNPs had sustainable efficacy on the control against A. citricola. By adding adjuvant GYT1602, compared with the same treatment without the addition, the control effects were all improved to a certain degree, there were significant difference in the 7 days after the first application, but no significant difference existed in the other days. It indicated that adding adjuvant could improve the quick effect.【Conclusion】It is recommended to use 2.25% DACNPs in initial occurrence of A. citricola. However, the combination of abamectin and dinotefuran at the ratio of 1∶4 should be used in peak occurrence to reduce the insect population density quickly. Adding adjuvant GY-T1602 in the spray could obtain a higher efficacy, especially in the early control effect.