Evaluating the Insecticidal Potential of Essential Oils against Rice Weevil (Sitophilus oryzae L.)

This study aimed to evaluate the adulticidal potential of five essential oils, garlic (Allium sativum), black pepper (Piper nigrum), lemongrass (Cymbopogon flexuosus), galangal (Alpinia galanga), and eucalyptus (Eucalyptus globulus) against the rice weevil, Sitophilus oryzae (L.), a major pest of stored grains worldwide. Laboratory bioassays were conducted from 4 August to 27 February under controlled conditions in West Bengal, representing the first comparative assessment of these oils against S. oryzae in this region. Each oil was tested at six concentrations (50, 100, 200, 500, 750, and 1000 ppm) on 20 adult weevils per replication, with three replications per treatment. Mortality was recorded over a 20-day period. Results demonstrated a clear dose-dependent and time-progressive mortality pattern. Garlic and black pepper were the most effective, achieving complete mortality by Day 10 at all tested concentrations, while galangal and lemongrass acted more slowly but showed steadily increasing mortality over time. Eucalyptus was the least effective, causing only 40–60% mortality even at higher doses. One-way ANOVA indicated significant differences among treatments, and probit analysis revealed low LC₅₀ values for garlic and black pepper, confirming their high potency. Grain weight loss analysis further demonstrated that treatments with more toxic oils reduced post-infestation damage. These findings suggest that essential oils, particularly garlic and black pepper, could be effectively integrated into sustainable pest management strategies, reducing reliance on chemical insecticides and protecting stored grains in West Bengal and similar agroecological regions. This study provides the first evidence of the comparative efficacy of these oils against S. oryzae in the region, highlighting their potential impact on local post-harvest pest management practices.