Insecticidal potency and biochemical activity of Beauveria bassiana and Cymbopogon schoenanthus extract on Sitophilus zeamais (Coleoptera: Curculionidae)

Abstract

Among the important postharvest challenges that pest grain infestation causes worldwide, one of the most destructive primary pests of cereal grains is the Sitophilus zeamais. The current study investigates and compares the biocontrol potential of the entomopathogenic fungus Beauveria bassiana and the ethyl acetate extract of Cymbopogon schoenanthus against S. zeamais in terms of evaluating insecticidal efficiency and biochemical effects on oxidative stress biomarkers. C. schoenanthus extracts yielded nine major bioactive compounds by GC-MS analysis, the predominant ones being α-eudesmol (43.9%), elemol (15.66%), and cryptomeridiol (13.38%). Bioassays indicated concentration-dependent mortality for both treatments: B. bassiana yielded 80.0% mortality at 14 days (LC₅₀: 1.08×10⁶ spores/ml), whereas C. schoenanthus extract yielded 73.0% (LC₅₀: 29.42 mg/ml). Both treatments reduced F₁ progeny production significantly by 81.5% (B. bassiana) and 70.6% (C. schoenanthus), where losses in weight of grains were only reduced to 2.4% and 5.2%, respectively compared to the 30% loss observed in controls. Biochemical evaluation indicated different responses to oxidative stress. C. schoenanthus extract caused chronic but manageable oxidative stress with the sustained rise of the antioxidant enzymes (catalase: 1.53-fold, superoxide dismutase: 1.28-fold, glutathione S-transferase: 1.34-fold), and mild lipid peroxidation by 44.1% MDA increase. B. bassiana exhibited a biphasic pattern: initial enzyme upregulation followed by the total collapse of the antioxidant system at day five (20-22% below control levels) accompanying severe oxidative damage (71.2% MDA increase), synchronizing with increased mortality. Both fungal and botanical biocontrol agents are promising eco-friendly alternatives to synthetic pesticides for stored grain pest management, as this study's findings show.