<p>Neonicotinoids such as imidacloprid and thiamethoxam remain widely used for managing the whitefly, <i>Bemisia tabaci</i>, yet intensive applications have selected for resistance in many production systems. Here, we quantified stage-resolved susceptibility to imidacloprid and thiamethoxam across eggs, second-instar nymphs, and adults in five field populations of <i>B. tabaci</i> molecularly confirmed as MEAM1 by COI sequencing and phylogenetic analysis. The study further examined whether population-level resistance patterns were associated with detoxification enzyme activity measured in adults. Standardized leaf-dip bioassays on colonies reared on eggplant under controlled conditions were analyzed by probit methods to estimate LC₅₀ values and resistance ratios (RRs) relative to a field-derived reference population (Marand). Across life stages, among-population differences were consistent, with Jiroft showing the highest LC₅₀ and RR values. In adults, imidacloprid resistance in Jiroft approached ~ 60-fold, whereas thiamethoxam resistance reached ~ 24-fold. Second-instar nymphs showed lower RRs than adults but still exhibited meaningful resistance (imidacloprid RR ≈ 15-fold in Jiroft), and eggs also displayed elevated tolerance relative to the reference population. In adult biochemical assays, resistant populations showed increased cytochrome P450 monooxygenase and glutathione S-transferase activities and/or elevated carboxylesterase activity, consistent with a metabolic component to resistance. These results delineate a life-stage-resolved resistance profile within a single MEAM1 lineage and under the present assay framework, second-instar nymphs appeared to be the most operationally responsive stage for potential intervention, but are no longer fully susceptible in highly selected populations, underscoring the value of stage-explicit monitoring in intensive vegetable systems.</p>