Field Efficacy of Different Insecticides against Flower Bud Thrips (Megalurothrips sjostedi Trybom) Infesting Cowpea at Gauradaha, Jhapa, Nepal

Flower bud thrips (Megalurothrips sjostedti Trybom) is one of the most noxious and major pests of the cowpea crop. This experiment was conducted in the cowpea field of Gauradaha Agriculture Campus, Jhapa, in 2024 to evaluate the efficacy of different treatments against flower bud thrips in cowpea. The field layout was designed as a Randomized Complete Block Design (RCBD) with 7 treatments and 3 replications, with the Karma Stickless variety. The insecticides tested were azadirachtin 300 ppm (3ml/L), Beauveria bassiana 1.15% WP (3g/L), Spinosad 45% SC (0.4ml/L), cypermethrin 10% EC (1.5ml/L), dimethoate 10% EC (2ml/L), imidacloprid 70% WG (0.3125 gm/L) and water (1.5l/plot) as a control. Treatments were applied by foliar spray method, and the impact on thrips population was measured on 2, 4 and 6 days after each of the three applications. The field experiment revealed a significant effect of insecticides on the thrips population after each spray. The highest mean Population Reduction Over Control (PROC) was observed with Spinosad (87.64%, 92.42%, and 81.80%) after the first, second, and third sprays, respectively, followed by dimethoate (83.13%, 86.57%, and 74.63%). Yield parameters also showed significant differences among insecticidal sprays, where the highest yield was recorded in Spinosad (15.96 mt/ha), with a length of 29.8 cm and a diameter of 10.0 mm, followed by Dimethoate (14.75 mt/ha), with a length of 29 cm and a diameter of 9.90 mm, respectively. Control plots showed the highest thrips populations and the least yield parameters throughout the observation period. The economic analysis further showed Spinosad to be economically viable with the highest yield (3.44 kg/2.16 m 2), gross return (NRs. 275.2), and best benefit-cost (B: C) ratio of 1.37. Hence, the study suggests that Spinosad is the most effective and economically viable insecticidal treatment in reducing thrips count and increasing yield.