Effects of five insecticides delivered by nanocarriers on the activity of Aphis citricola and the safety of Harmonia axyridis

To clarify the insecticidal activity, field efficacy, and impact of five insecticides (avermectin, thiamethoxam, imidacloprid, sulfoxaflor, and matrine) delivered by a star polycation (SPc) on Aphis citricola, and its impact on Harmonia axyridis, indoor bioassays using the leaf soaking method were conducted to assess the insecticidal activity of SPc-delivered insecticides against A. citricola and field efficacy trials were also performed to study the control of A. citricola. The effects of SPc-delivered insecticides on the hatching of H. axyridis eggs were evaluated using an immersion method, and the impact on the survival rate of H. axyridis larvae was determined via the topical application method. Bioassay results revealed that after using SPc delivery, the LC₅₀ values of the five insecticides against A. citricola were reduced by 29.05% to 48.30% compared to the original commercial formulations, indicating that SPc improved the insecticidal activity of the five insecticides. SPc-delivered insecticides showed no significant impact on the egg-hatching rate of H. axyridis, although they increased the mortality rate of H. axyridis larvae. However, compared with the original commercial formulations, the differences were negligible. Field trials demonstrated that when the five insecticides were delivered using SPc, the field efficacy against A. citricola increased by 0.68% to 7.57% compared to the original commercial formulations after 3 days of treatment, indicating that SPc delivery can improve the rapid efficacy of insecticides. After 14 days of treatment, the high-dose treatment of the five insecticides delivered by SPc showed a 3.95% to 6.96% increase in efficacy compared to the original commercial formulations, indicating that SPc delivery can also significantly improve the persistence of insecticides. The research suggests that SPc-delivered insecticides can significantly enhance their activity against A. citricola, and improve field efficacy without notably affecting H. axyridis.