Effect of binary combinations of neem oil and Hymenocardia acida (Anacardiaceae) and Lophira lanceolata (Ochnaceae) wood ashes against Sitophilus zeamais (M.) (Coleoptera: Curculionidae) and Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae)

Abstract

Maize and cowpeas play a fundamental role in combating food insecurity in sub-Saharan Africa, particularly in Cameroon. As major sources of carbohydrates and vegetable protein, these crops are staple foods for low-income rural populations. Their regular consumption contributes significantly to meeting nutritional needs and reducing poverty. However, post-harvest losses caused by the main insect pests of maize, S. zeamais, and cowpea, C. maculatus, compromise the availability of these commodities throughout the year. In response to this problem, we evaluated the insecticidal efficacy of binary combinations of neem oil and wood ash from H. acida and L. lanceolata as a sustainable alternative to synthetic insecticides. The results show that all the products tested (neem oil, ashes and their mixtures) cause significant mortality in pests, proportional to the dose and duration of exposure. Neem oil proved to be particularly effective, achieving up to 100% mortality at high doses. The ash from H. acida showed higher toxicity than that from L. lanceolata. The neem oil + ash mixtures demonstrated notable synergistic effects, reducing the doses required while increasing efficacy, particularly against S. zeamais. The study also confirms the repellent power of the plant-based products on S. zeamais, their ability to significantly reduce the fertility and offspring production of C. maculatus, with inhibition of up to 99.33%. Neem oil and ash from H. acida and L. lanceolata, alone or in combination, are promising, sustainable and accessible alternative methods for protecting grain stocks in sub-Saharan Africa.