Evaluation of the efficacy and safety of root drenching with neonicotinoid insecticides against honeysuckle aphids

The occurrence period of honeysuckle aphids overlaps with the harvesting season of honeysuckle, and the conventional practice of insecticide spraying for aphid control may pose safety risks to honeysuckle. In this study, the efficacy of 70% thiamethoxam water dispersible granules (WG) and 70% imidacloprid WG against honeysuckle aphids was evaluated using the root-drenching method, and the residue levels of the pesticides in honeysuckle plants were determined at 14, 21, 28, 35, and 45 days after treatment. Field efficacy trials showed that a single early-season root-drench application of 70% thiamethoxam WG (0.75, 1.50, and 3.00 g a.i./hm²) or 70% imidacloprid WG (1.50 and 3.00 g a.i./hm²) provided 73.71%-99.96% and 71.77%-100.00% control efficacy against honeysuckle aphids, respectively, from 7 to 28 days after application. Residue analysis results in flowers showed that, except for thiamethoxam at the 3.00 kg/hm² application rate 21 days after treatment (0.71 mg/kg), all residue levels were below the maximum residue limit (0.50 mg/kg) specified by China's National Food Safety Standard (GB 2763—2021). In stem and leaf tissues, the residue levels of thiamethoxam and imidacloprid remained as high as 2.80 and 2.00 mg/kg, respectively, even 45 days after application, providing direct evidence of their sustained control of honeysuckle aphids. In conclusion, root drench applications of 70% thiamethoxam WG treatments (0.75 and 1.50 a.i. kg/hm²) and 70% imidacloprid WG treatments (1.50 and 3.00 a.i. kg/hm²) provided efficient and long-lasting control of honeysuckle aphids, with the residue levels conforming to the national food safety standard.