PERTANIKA JOURNAL OF TROPICAL AGRICULTURAL SCIENCE

The rice brown planthopper (BPH), Nilaparvata lugens (Stål.), is a highly damaging insect pest to rice crops. The excessive use of synthetic chemicals has resulted in the development of resistance to insecticides and negative consequences for the environment and insect biodiversity. Hence, three common weed species, namely Ageratum conyzoides, Chromolaena odorata, and Mallotus paniculatus, were evaluated on the comparative extraction yield in different solvents, as well as the toxicity potential in the selected methanol extract. Further, the bioactive compounds in C. odorata were characterized, and potential bio-insecticide formulations were developed and evaluated on the BPH. Methanol extract displayed higher efficiency, yielding 17.29% compared to only 3.19% in hexane extract. Insecticidal activity evaluation demonstrated that C. odorata exhibited the highest toxicity (77.50% at 10,000 ppm), having a median lethal concentration (LC₅₀) value of 977 ppm, while A. conyzoides (55.20% at 10,000 ppm) and M. paniculatus (60.0% at 12,000 ppm) produced LC₅₀ values of 6,549 ppm and 21,940 ppm, respectively. Subsequently, a plant-based bio-insecticide was formulated using the crude methanol extract of C. odorata as the active ingredient. A mixture of surfactant (Emersense® AM 8025), oil (palm kernel oil ester), and water resulted in a stable macroemulsion called Emersense® AM 8025/palm kernel oil ester/water (EM-PKOE). The formulated macroemulsion displayed enhanced toxicity and efficacy against BPH nymphs, with an LC₅₀ value of 220 ppm, outperforming the unformulated crude methanol extract (977 ppm). Chemical composition analysis using gas chromatography-mass spectrometry revealed that C. odorata primarily contained sesquiterpenes (24.14%). This study proposes C. odorata as a potential bio-insecticide for BPH combatants, necessitating further research on the formulation for eventual commercialization to sustainable BPH control in rice cultivation.

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