Examination of the sensitivity of peach orchard aphids to imidacloprid and afidopyropen

【Objective】Green peach aphid and peach mealy aphid are pests causing significant harm to peach trees and other crops worldwide. They primarily feed by sucking plant sap, resulting in leaf damage that affects the growth, development, and photosynthesis of peach trees. Simultaneously, they pose a threat to the health and yield of peach trees and other crops by transmitting viruses. Control of the peach aphids has traditionally relied on chemical methods. However, due to characteristics such as large population sizes, short life cycles, high reproduction rates, and strong migratory capabilities, these aphids have developed varying degrees of resistance to many commonly used insecticides. Therefore, monitoring the sensitivity of the peach aphids to common insecticides is particularly important. This not only helps in assessing the actual effectiveness of the pesticides but also enables timely adjustments in control strategies based on the degree of resistance development. By doing so, the emergence of resistance can be delayed or avoided, leading to more precise pest management measures and thus achieving sustainability in agriculture. The populations of Myzus persica and Hyalopterus amygdali were collect-ed from peach orchards in different peach-producing areas in China during 2022 and 2023 to monitor the sensitivity to imidacloprid and afidopyropen.【Methods】The toxicity levels of these aphids to the insecticides were determined using the glass tube film methods. The active pharmaceutical ingredient of imidacloprid and afidopyropen were diluted with acetone to prepare a master stock solution for subsequent experimentation. An aliquot of 250 μL insecticide- acetone solution was applied to each tube (length: 7.5 cm; diameter: 1.2 cm, internal surface area: 27.51 cm2 ), and they were immediately rotated using a micro- rotator (American Wheaton Company) until solutions were dried. These peach aphids were treated for each concentration with three replicates, while controls were treated with acetone only. The tubes were then placed under laboratory conditions. After 24 h, mortality was recorded, and individuals were deemed dead if they showed no response when prompted with a brush.【Results】The monitoring results of 2022 showed that the M. persica population from Jiaxing city of Zhejiang province was found to be most sensitive to imidacloprid, with an LC50 of 0.222 mg·L-1 . In contrast, the M. persica population from Qinhuangdao city of Hebei province, Xi’an city of Shanxi Province, and Lanzhou city of Gansu province exhibited lower sensitivity. These results suggest a significant variation in the response to imidacloprid across different geographic locations, potentially influenced by environmental and genetic factors. In the subsequent year, the M. persica population from Hangzhou city of Zhejiang province displayed the highest sensitivity to imidacloprid, though with an increased LC50 of 1.574 mg ·L- 1 . Comparative analysis of the two years monitoring data revealed that the sensitivity of the M. persica from Qingdao city of Shandong province to imidacloprid remained relatively stable. While a decreasing trend in sensitivity was observed in the M. persica from Xianyang city of Shanxi province, underscoring the dynamic nature of pesticide resistance. As for afidopyropen, the M. persica population from Qinhuangdao city of Hebei province, was most sensitive in 2022, with an LC50 of 0.011 mg·L-1 . In 2023, the M. persica from Hangzhou city of Zhejiang province was most sensitive with an LC50 of 0.159 mg·L-1 . Comparative analysis found that the sensitivity of the M. persica population to afidopyropen showed an increasing trend from Lanzhou city of Gansu Province. The monitoring results of the H. amygdali indicated that the population from Kunming city of Yunnan province exhibited the highest sensitivity to both imidacloprid and afidopyropen. This observation is crucial as it points to possible interspecies differences in how the resistance mechanism is developed and managed. In contrast, the sensitivity of the H. amygdali to imidaclorpid significantly decreased from Qinhuangdao city of Hebei province and Suzhou city of Anhui province, highlighting the need for ongoing monitoring and adaptive management strategies.【Conclusion】The results of this study indicated significant regional and annual variations in the susceptibility of the M. persica and H. amygdali to common used insecticides imidacloprid and afidopyropen, respectively. These variations might be associated with factors such as the history of insecticides use, environmental conditions, and the genetic diversity within the populations. Therefore, it is imperative to consider these factors when devising pest control strategies, implementing targeted measures to enhance control efficiency and slow down the development of resistance. This comprehensive approach would not only clarity the causes behind the varying pesticides sensitivities but also aid in the development of more effective pest management strategies. Moreover, continuous monitoring of the changes in pest sensitivity to insecticides is crucial for effective pest management and sustaining agricultural development. Rotating insecticides with different mechanisms of action, reducing the frequency of specific insecticide usage, and conducting in-depth research into the molecular mechanisms behind reduced sensitivity in specific regions would contribute to delaying the development of insecticide resistance in pests.