Evaluation of sustainable biorational pesticides for managing Helicoverpa armigera (Lepidoptera: Noctuidae) on tomato in Nepal

Abstract Helicoverpa armigera (Hübner) [Lepidoptera: Noctuidae] is a highly polyphagous pest leading to a substantial yield loss of tomato crop globally, including in Nepal. The increasing use of harmful pesticides to control this pest has resulted in severe environmental impacts and human health hazards. To evaluate alternative solutions, an experiment was conducted in Rupandehi District, Nepal assessing the efficacy of six biorational pesticides against H. armigera. The tested treatments included: Pacer® [ Metarhizium anisopliae (Metsch.) 1% WP @ 5 g/L], Mahastra® ( Bacillus thuringiensis var. kurstaki @ 2 g/L), Tracer® (Spinosad 45 SC @ 0.3 ml/L), Neemraj Super® (Azadirachtin 3000 ppm @ 5 ml/L), Biotrine® (Abamectin 5 EC @ 1 ml/L), and Alcora® (Chlorantraniliprole 18.5 SC @ 0.4 ml/L). The study employed a randomized complete block design (RCBD) to ensure robust statistical analysis of treatment effects. The pesticide treatments were applied four times at 15—day intervals. H. armigera population density per plot was recorded 3, 7 and 10 days after each application. Biological yield and marketable yield were assessed 93 days after transplantation. The effects of each treatment were assessed by comparing the mean H. armigera infestation scale, the percentage reduction in larval population relative to the control, and both biological and marketable yields. Among all treatments Chlorantraniliprole demonstrated superior efficacy, achieving an 87% reduction in larval populations compared to the control. This treatment also yielded the highest marketable fruit production (21.85 t/ha) and the most favourable benefit–cost ratio (6.53). Spinosad showed a 79% reduction in pest population, a marketable yield of 21.57 t/ha, and a benefit–cost ratio of 6.14 ranking as the second most effective treatment. The microbial and botanical pesticides showed moderate efficacy. Although being less efficient Azadirachtin was found to be more economical than Abamectin. Therefore, this study guides to the development of integrated pest management (IPM) strategies by including locally produced botanicals to combat tomato fruit borers in Nepal.