Evaluation of three biopesticides on the invasive pest Spodoptera frugiperda Smith, 1797 (Lepidoptera: Noctuidae), infesting maize crops (Zea mays L., 1753) in upper Casamance

The invasion of the pest, Spodoptera frugiperda in Senegal in 2017, has increased pest pressure on crops. The excessive use of pesticides leads to harmful effects on the environment. Thus, the objective of this study is to compare the effectiveness of biopesticides with that of chemical molecules currently used on S. frugiperda. The work was carried out at the support center for Pre-extension and Multilocal Experimentation of Velingara, in Haute Casamance, in a Fisher block system. The efficacy of biopesticides (Bacillus thuringiensis var kurstaki, and Spodoptera frugiperda Multiple Nucleopolyhedrovirus (SfMNPV)) as well as that of the hydro-ethanolic extract of Ocimum gratissimum was evaluated. It was compared to that of an absolute control and a combination of chemical molecules, Emamectin benzoate 20 g/l combined with Lufenuron 80 g/l (EBL) used as a reference control. The results showed that the three bio-insecticides B. thuringiensis, SfMNPV and O. gratissimum extract are toxic on S. frugiperda larvae with efficacy rates of 70%, 52% and 64%, respectively. However, SfMNPV is less effective than the reference control. All these bio-insecticides have also effectively reduced the damage of the pest on plants, especially B. thuringiensis, which has an effectiveness equivalent to that of EBL. As for the damage to the harvested ears, B. thuringiensis and O. gratissimum have a suitability comparable to EBL. However, SfMNPV, although as effective as other bio-insecticides, is less marked than EBL in reducing ear damage. This study demonstrates the effectiveness of bioinsecticides used on S. frugiperda.