Evaluation of the insecticidal activity of the extracts of Trichilia emetica, Trichilia capitata, and Azadirachta indica against the Spodoptera frugiperda (Fall Armyworm) on maize crop

Abstract

Plant extracts contain many active compounds called secondary metabolites, which are tremendously fruitful for plant defense against several insect pests. The main objective of the present study was to evaluate the aqueous and ethanolic plant extracts of Trichilia emetic , T. capitata, and Azadirachta indica for their insecticidal activity against Spodoptera frugiperda known as fall armyworm on maize crop as well as the preliminary phytochemical evaluation. All extracts were prepared using a Soxhlet apparatus, the insecticidal activity was performed on the disc immersion diffusion method, and the preliminary phytochemical analysis was done using the classical methods. The concentrations of the extracts for the insecticidal activities ranged from 0.01 to 1% (w/v). The third instar larvae of S. frugiperda were fed with corn leaves treated with these extracts, separately. Ethanol and distilled water were used as controls. The results showed a strong insecticidal activity of the extracts of the three plants tested, with LC 50 of 0.212 for the aqueous extract of the leaves of T. emetica ; 0.155 for aqueous extract of the stem bark of T. emetic a; 0.12 for aqueous extract the leaves of T. capitata ; 0.051 for aqueous extract of the stem bark of T. capitata , and 0.13 for aqueous extract of the leaves of A. indica . These activities were dependent on the concentration, in which the stem barks aqueous extract of T. capitata , with LD 50 of 0.051% was the most active. The preliminary phytochemical analysis was carried out on all extracts to identify the secondary metabolites that could be related to the observed insecticidal activities. All the extracts showed the presence of flavonoids, anthraquinones, and condensed tannins. Alkaloids and glycosides were detected in all extracts except for the leaves aqueous extract of A. indica . However, T. capitata was evaluated for the first time for the biological activity as well as the phytochemical analysis. It could be concluded that all the plant extracts possessed significant insecticidal properties and could be introduced as botanical insecticides after field evaluations.