Helicoverpa armigera, a global polyphagous pest, attacks a wide variety of crops causing huge agricultural loss. Overuse of conventional insecticides for Helicoverpa control has made Helicoverpa resistant to insecticides leading to more severe attacks on crops diverting interest of researchers to explore alternate control agents. Present study investigates the cidal and antifeedant potential of Emamectin benzoate; a semi-synthetic avermectin derived from the soil actinomycetes, Streptomyces avermitilis; against early IV instars of H. armigera. Larvae were fed on the castor leaf discs (3.5 cm diameter) dipped in different concentrations of Emamectin benzoate; ranging from 0.05 µg/mL-1.5 µg/mL. The leaf disc areas were measured pre-and post-larval feeding to estimate the antifeedant potential of compound. The effect of feeding was also assessed on the survival of larvae by scoring the larval mortality till 96 h. Our investigations showed significant larvicidal potential of Emamectin benzoate against H. armigera revealing respective LC 50 values of 0.26 µg/mL, 0.095 µg/mL, 0.043 µg/mL and 0.027 µg/mL after 24, 48, 72 and 96 h feeding. Furthermore, a remarkable decrease of 93.59% was observed in larval feeding potential indicating significant antifeedant efficacy of Emamectin benzoate. A strong correlation between antifeedant index and the Emamectin benzoate concentration resulted in 1.48-fold index reduction with a decrease in concentration. Our results demonstrated efficacy of Emamectin benzoate as an effectual larvicidal and antifeedant agent against H. armigera. Employing selective insecticide can tackle issues of pest resistance and pest resurgence after ascertaining in the fields as Helicoverpa control agent and negating impact on non-target organisms.
Helicoverpa armigera is a global agricultural pest of serious concern. Continued use of chemical insecticides as control measures has raised grave health and environment concerns, necessitating a search for botanicals as safe alternatives. The current study investigates the effects of ?-sitosterol, a bioactive phytocomponent in Thevetia neriifolia, on the growth and development, as well as on midgut enzymes of H. armigera. Dietary ?-sitosterol produced dose-dependent systemic toxicity and growth inhibitory effects in H. armigera; the most significant effects were obtained with 10 ?g/mL dietary ?-sitosterol. Higher prepupal and pupal mortality in comparison to larval mortality and a comparatively greater reduction in average weight gained by later instars point to cumulative effects of ?-sitosterol. The delayed effects were ascertained by the 82.05%-57.89% reduction in adult emergence in comparison to 95.02% emergence in controls. Dose-dependent effects of ?-sitosterol were observed as significantly decreased enzyme activities of alanine aminotransaminase (ALT), aspartate aminotransaminase (AST) and alkaline phosphatase (ALP) in the larval midgut. Suppression of enzyme activity was obtained in the order ALT>AST>ALP. Impaired activity of gut enzymes possibly lowered the energy reserves and affected nutrient transport through the gut epithelium, affecting the growth and development of H. armigera. Our study points to a promising use of ?-sitosterol against H. armigera, although further examination and field studies are needed to ascertain its possible use in control programs.
Aedes aegypti is responsible for the global spread of several ailments such as chikungunya, dengue, yellow fever, and Zika. The use of synthetic chemicals is the primary intervention in mosquito management. However, their excessive utilization resulting in the spread of toxic ingredients in the environment and posing threats to beneficial organisms has prompted the recommendation for the use of biologically synthesized nanocomposites as a promising approach for vector control. Silver nanocomposites were synthesized using leaf (AL-AgNCs) and stem (AS-AgNCs) extracts of Achyranthes aspera. The early fourth instars of A. aegypti were exposed to lethal doses of these nanocomposites to evaluate their effects on larval development, behavior, morphology, and mid-gut histoarchitecture. The cellular damage and deposition of nanocomposite residues in the mid-gut were studied using light and transmission electron microscopy. The A. aspera silver nanocomposite (AA-AgNC)-exposed larvae exhibited dose-dependent extended duration of development and diminished adult emergence, but did not exhibit modified behavior. Intense damage to the cuticle membrane and slight contraction in the internal membrane of anal papillae were noticed. Morphologically, the mid-gut appeared disorganized, darkly pigmented, and shrunk. Histological investigations of the mid-gut revealed significantly disordered internal architecture with lysed cells, damaged peritrophic membrane and microvilli, disintegrated epithelial layer, and a ruptured and displaced basement membrane. Visualization of the larval mid-gut through TEM showed severe cellular damage and aggregation of black spots, indicating the deposition of silver particles released by AA-AgNCs. The investigations revealed the bio-efficacy of A. aspera-mediated AgNCs against A. aegypti inducing stomach and contact toxicity in the larvae. The utilization of AA-AgNCs is recommended for A. aegypti management as a safe and effective intervention.
Present investigation attempts to study binding of β-sitosterol with Helicoverpa armigera midgut enzymes; alanine aminotransaminase (ALT), aspartate aminotransaminase (AST) and alkaline phosphatase (ALP); through docking-based virtual screening. Extraction of the protein sequence of the enzymes revealed a respective linear chain of 535, 522 and 430 amino acids for ALP, ALT and AST. The binding energy for ALT-ligand complex was lowest as compared to the AST and ALP-docked complexes. The ALT-docked complex had ligand efficiency of (-) 0.32 with an inhibition constant of 104.01, more hydrogen bonds and hydrophobic interactions leading to a more stable complex. However, unfavored bumps in AST and ALP complexes may have led to comparatively unstable complexes. The dietary β-sitosterol exhibits differential binding with midgut enzymes of H. armigera larvae. The strong binding of β-sitosterol with ALT indicates the highest inhibition of ALT activity due to the activity-stability trade-off. The enzymes, AST and ALP exhibited relatively higher activity as a resultant of lesser stabilization of the β-sitosterol-enzyme complex. In silico studies have indicated that β-sitosterol can be used an effective control agent against H. armigera.
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