Population Dynamics, Pesticide Efficacy, and Residue Profiles of Thrips tabaci on Onion Across Two Seasons

Onion thrips (Thrips tabaci) limit onion production globally, causing considerable yield loss. This two-season field study (December–April, 2023–2025) investigated thrips population dynamics, evaluated the efficacy of Ignar 20% SC (abamectin + spirodiclofen) and Danisaraba 20% SC (cyflumetofen), and quantified pesticide residues in soil, green onion leaves, and bulbs using LC-MS/MS. Thrips populations peaked between February and March during the bulbing stage. Generalized additive models indicated that crop age had the strongest positive association with thrips populations in both seasons, while the impacts of humidity, rainfall, and temperature varied. Both pesticides substantially reduced thrips numbers compared to untreated controls, with Ignar 20% SC proving more effective than Danisaraba 20% SC. Residue analysis revealed that abamectin levels were consistently lowest across all matrices (0.0019–0.0072 mg kg−1), whereas spirodiclofen and cyflumetofen residues ranged from 0.0247 to 0.0372 mg kg−1. MRL compliance was highly jurisdiction-specific: abamectin bulb residues were below all established limits, but spirodiclofen and cyflumetofen exceeded EU limits, with no Codex or US EPA limits established for these two compounds on onions. These results support population suppression approaches combining crop-age monitoring with targeted pesticide treatments and emphasize the need for jurisdiction-specific residue monitoring to meet export market MRLs.