Abstract
The present research investigated the chemical characterization and insecticidal activity of n-Hexane extracts of Epaltes divaricata (NH-EDx) along with their chief derivatives n-Hexadecanoic acid (n-HDa) and n-Octadecanoic acid (n-ODa) against the dengue vector Aedes aegypti and lepidopteran pest Spodoptera litura. Chemical screening of NH-EDx through GC–MS analysis delivered nine major derivatives, and the maximum peak area percentage was observed in n-Hexadecanoic acid (14.63%) followed by n-Octadecadienoic acid (6.73%). The larvicidal activity of NH-EDx (1000 ppm), n-HDa (5 ppm), and n-ODa (5 ppm) against the A. aegypti and S. litura larvae showed significant mortality rate in a dose-dependent way across all the instars. The larvicidal activity was profound in the A. aegypti as compared to the S. litura across all the larval instars. The sublethal dosages of NH-EDx (500 ppm), n-HDa (2.5 ppm), and n-ODa (2.5 ppm) also showed alterations in the larval/pupal durations and adult longevity in both the insect pests. The enzyme activity revealed that the α- and β-carboxylesterase levels were decreased significantly in both the insect pests, whereas the levels of GST and CYP450 uplifted in a dose-dependent manner of NH-EDx, n-HDa, and n-ODa. Correspondingly, midgut tissues such as the epithelial layer (EL), gut lumen (GL), peritrophic matrix (Pm), and brush border membrane (BBM) were significantly altered in their morphology across both A. aegypti and S. litura against the NH-EDx and their bioactive metabolites. NH-EDx and their bioactive metabolites n-HDa and n-ODa showed significant larvicidal, growth retardant, enzyme inhibition, and midgut toxicity effects against two crucial agriculturally and medically challenging insect pest of ecological importance.
Highlights
Phytochemicals are generally secondary metabolites that aid as a solid defensive action in plants against the constant selection pressure of herbivore predators, microbial pathogens, and other ecological risks [1]
The midgut cells were severely infected in the fourth instar larvae of A. aegypti after treatment with sublethal dosages of NH-EDx (500 ppm) (Figure 11B), n-Hexadecanoic acid (n-HDa) (Figure 11C), and n-Octadecanoic acid (n-ODa) (Figure 11D) as compared to the control (Figure 11A)
The fourth instar larval midgut cells of S. litura were significantly affected after treatment with sublethal dosages of NH-EDx (Figure 11F), n-HDa (Figure 11G), and n-ODa (Figure 11H) as compared to the control (Figure 11E)
Summary
Phytochemicals are generally secondary metabolites that aid as a solid defensive action in plants against the constant selection pressure of herbivore predators, microbial pathogens, and other ecological risks [1]. Global researchers have proved that plant extracts and their bioactive compounds predominantly control harmful agriculture pests and disease-spreading arthropods with similar toxicity as displayed by chemical pesticides [6,7,8]. S. litura is a firm flier and splits a wide-ranging distance annually all over the summer season It is recognized as the most harmful agriculture pest of tropical nations such as China, Japan, and India, as it causes significant financial damage to diversified vegetables and grain crops [15,16]. Previous research on diverse plant extracts and chief metabolites against mosquito vectors or agriculture pests has delivered that many botanical sources proved as potential alternatives, or as rotational chemistries, to heavily-used synthetic chemical insecticides [30].
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