Résumé
Fall armyworm (FAW), Spodoptera frugiperda, is a major pest of maize worldwide. Since its first report in West Africa in 2016, FAW has quickly spread causing severe outbreaks and crop losses. Chemical control remains the primary management option despite its adverse effects and its increasing inefficiency but safer and more effective alternatives exist. Here, we investigated the effectiveness of two bioinsecticides, a microbial and a botanical ones, in reducing the damage caused by FAW larvae to maize leaves and cobs, and their effects on yield. This was compared to that of two chemicals commonly used against FAW, deltamethrin- and a binary lambda-cyhalothrin and acetamiprid-based insecticides. A field trial was conducted in 2018 and 2019 in northwestern Senegal using a randomized complete block design. Without treatment, 1–25% of the total leaf area and 3–44% of the maize cobs were damaged by FAW. Despite different levels of damage between the two years, the same pattern was revealed with insecticide applications. Although deltamethrin insecticide may, in some years, reduce defoliation and cob damage, the effect of chemical insecticides, if any, was not reproducible, and maize yield was not improved. In contrast, azadirachtin and Bacillus thuringiensis formulations significantly reduced FAW damage on leaves. The proportion of damaged cobs could also be reduced by a factor of between 2 and 7.5 and the total maize yield was at least doubled. The scope of our results is discussed in the context of S. frugiperda control, particularly in Integrated Pest Management programmes and farmers’ practices.