Evaluation of insecticide resistance in different field populations of Cabbage aphid, Brevicornye brassicae  (Hemiptera: Aphididae) to selected organophosphate insecticides

The Cabbage aphid, Brevicoryne brassicae is the most devastating pest of cruciferous crops, and management strategies mainly rely on insecticidal treatment. In this study, we evaluated the susceptibility of different field populations of B. brassicae collected from eight major cruciferous crop-producing districts of Kashmir, India, in 2023. The Toxicity of Chlorpyrifos (25% EC Kohiban), Dimethoate (30% EC Tafgor), and Quinalphos (25% EC Flash) was evaluated by foliage spray method under laboratory conditions. Different populations showed varied levels of susceptibility to the insecticides evaluated at various concentrations. The variability of the LC ₅₀ values was 3.71 mlL ^− 1 for dimethoate, 4.61 mlL ^− 1 for chlorpyrifos, and 3.97 mlL ^− 1 for quinalphos. After comparing insecticides resistance ratios (RR) with most susceptible field populations, resistance ratio to quinalphos was highest in the range of 1.13-3.07-fold, followed by 1.10-2.17-folds for dimethoate and 1.07-2.9-fold for Chlorpyrifos. The highest level of resistance to dimethoate was found in Budgam (LC ₅₀  = 7.32 ml ^L−1 ) and lowest in Anantnag (LC ₅₀  = 2.52 ml L ^− 1 ). Resistance against quinalphos was highest in Baramulla (LC ₅₀  = 8.45 mlL ^− 1) and lowest in Anantnag (LC ₅₀  = 2.75 mlL ^− 1 ). When exposed to the same insecticide, Bandipora exhibits the lowest resistance (LC ₅₀  = 3.18 mlL ^− 1 ) and Anantnag the highest resistance (LC ₅₀  = 6.92 mlL ^− 1 ). Rotation of insecticides with different modes of action where populations have no, very low, or low levels of resistance could be helpful in the management of B. brassicae infestation.