Insecticidal activity of Delonix regia (Fabaceae) against the cotton leafworm, Spodoptera littoralis (Bois) with reference to its phytochemical composition

Abstract

Overuse of synthetic pesticides causes problems for humans and the environment or leads to insect resistance to insecticides, so plant extracts and essential oils have gained popularity as an environmentally acceptable alternative to chemical pesticides. This study investigated the toxicity of Delonix regia leaf and seed extracts, protein patterns, and genetic distance analysis against the 5th instar larvae of cotton leafworm, Spodoptera littoralis Boisaduval. Methanol, petroleum ether, and acetone extracts of leaves and seeds of D. regia were used to coat castor leaves for ingestion by the 5th instar of S. littoralis larvae. The seeds' methanol and petroleum ether extracts were the most effective (100 and 98 Mortality%), with LC₅₀ values of 0.887 and 1.795 g/L, respectively, 24 h post-treatments. Data showed that D. regia extracts affected consequences of protein changes compared to untreated S. littoralis larvae resulted in genetic changes, as well as inhibition of the insect's important α-amylases, forming protein complexes, and influencing normal growth and development. GC-MS analysis of the chemical composition of the seed extract revealed 18 compounds with high levels of stigmasterol, 2-methyl-4-vinylphenol, benzoic acid, 3-hydroxy, and squalene with percentages of 43.07%, 21.33%, 14.51%, and 14.12%, respectively. As a result, we concluded that D. regia seed extracts had the potential to control Spodoptera littoralis larvae.