Toxicity of Bioactive Compounds of Strychnos pseudoquina (Loganiaceae) in Spodoptera frugiperda (Noctuidae)

The objective of this study was to assess the toxicity of leaf and bark extracts of Strycns pseudoquina and their fractions, as well as flavonoids isolated from its bark, in a population of Spodoptera frugiperda. Crude bark and leaf extracts, as well as fractions of these extracts, were obtained using a rotary evaporator and different solvents; the ethyl acetate fraction was obtained, and flavonoid compounds were isolated, consisting mostly of 3-O-methylquercetin and minimally of strychnobiflavone. The crude extracts, extract fractions, and isolated flavonoids were applied separately to maize leaves, which were offered to S. frugiperda larvae; then, biological parameters of this insect population were evaluated. Toxic effects of topical applications of the isolated flavonoids on the larvae were also evaluated. The results highlighted the larvicidal effects of the crude bark extract and its fractions and the significant toxicity of this crude extract (LC50 = 0.048%), which was six times more toxic to larvae than its ethyl acetate fraction (LC50 = 0.288%). The investigated flavonoids showed no significant larvicidal effect. The pronounced larvicidal effect of S. pseudoquina bark crude extract and its fractions on S. frugiperda indicates that this plant presents an insecticidal potential to be explored in integrated pest management programs.