Enhancing insecticide efficacy: synergistic and sublethal impacts of a pirimicarb-imidacloprid mixture on Myzus persicae Sulzer (Hemiptera: Aphididae).

Abstract

Aphid resistance to insecticides necessitates management strategies that improve efficacy while minimizing chemical input, including combinations of active ingredients with distinct modes of action. This study evaluated the individual and combined toxicity of pymetrozine, pirimicarb, and imidacloprid against third-instar nymphs and adults of the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). Using a 48-h leaf-dip bioassay, insecticides were tested individually and in 1:1 binary combinations, and interactions were quantified using the combination index (CI). Sublethal effects of the most effective mixture were further assessed at the LC30 level (16.424 mg l-1) using age-stage, 2-sex life table analysis and biochemical assays. Among the tested combinations, the imidacloprid-pirimicarb mixture produced the strongest combined effect (CI < 0.5) in both developmental stages, whereas the other mixtures showed antagonistic interactions (CI > 1). This mixture resulted in LC50 values of 39.269 mg l-1 for nymphs and 122.553 mg l-1 for adults, corresponding to substantial reductions in effective concentration and active ingredient requirements compared with single-insecticide treatments. Sublethal exposure significantly (P < 0.05) reduced demographic parameters, including the intrinsic rate of increase (r), net reproductive rate (R0), fecundity, and longevity. Biochemical assays also revealed developmental stage-dependent alterations in acetylcholinesterase, esterase, and total protein levels following exposure to the mixture. Overall, the findings demonstrate that the imidacloprid-pirimicarb combination enhances toxicity against M. persicae under laboratory conditions and may contribute to reduced insecticide input, although additional studies are required to clarify the nature of the interaction and evaluate its applicability under field conditions.