Comparative efficacy of four biopesticides against Oryctes monoceros Olivier (Coleoptera: Dynastidae), a pest of oil palm in Côte d’Ivoire

The excessive use of synthetic insecticides in the phytosanitary protection of oil palm poses risks to public health and the environment. The aim of this study was to compare the efficacy of four (4) biopesticides against Oryctes monoceros, a pest responsible for delayed growth and, in some cases, the death of young oil palm plants. After obtaining larvae and adults from insect rearing, four biopesticides (A, B and C) at different concentrations (3.7×10–3 g/mL, 6.8×10–3 g/mL, and 1.2×10–2 g/mL), and biopesticide D (1.4×10–3 g/mL, 2.7×10–3 g/mL, and 4.8×10–3 g/mL) were first evaluated on Oryctes monoceros larvae. The larvae were exposed to the toxic effects of 100 mL of each prepared solution applied to 500 g of moistened wood sawdust. Among the four biopesticides tested, only biopesticide D, based on azadirachtin, showed high lethal efficacy, causing elevated larval mortality comparable to that of the reference insecticide. The respective lethal dose causing 10% mortality and lethal dose causing 50% mortality (LD50) values of 6.03×10–4±2.46×10–1 g/mL and 2.38×10–3±9.16×10–2 g/mL were lower, indicating higher efficacy. Compared to the reference synthetic insecticide cypermethrin, biopesticide D against adults showed an LD50 and a lethal dose causing 90% mortality (LD90) of 7.04×10–3±7.36×10–2 g/mL and 2.34×10–2±2.11×10–1 g/mL, respectively, while Cypermethrin yielded an LD50 and LD90 of 3.90×10–6±2.58×101 g/mL and 1.49× 10–4±1.75×101 g/mL. These results demonstrate the significant insecticidal activity of the biopesticides tested, particularly biopesticide D, against both larvae and adults of Oryctes monoceros. This product could be used as an alternative to synthetic chemical pesticides in the management of this pest.