Characterization and insecticidal effects of the essential oil and nanoemulsion of Pogostemon cablin on populations of Sitophilus zeamais

Insect pests pose significant risks to stored grains worldwide, and while synthetic pesticides are effective, they have environmental and health drawbacks. Plant essential oils (EO), with insecticidal properties, offer a promising alternative. This study evaluated the toxicity of Pogostemon cablin (patchouli) EO and its nanoemulsion on nine populations of Sitophilus zeamais, a major pest of stored grain. Fifteen compounds were identified in the EO, of which patchoulol was the major compound (55.04 %). The EO was tested through topical, contact, and fumigation exposures. Repellency and population growth effects were also assessed. The EO demonstrated fast insecticidal action, with an average median lethal time (LT₅₀) of 53 h. All populations showed similar responses, with the Viçosa population being the most susceptible, and Sete Lagoas the most tolerant. EO and nanoemulsion concentrations required to cause 50 % mortality ranged from 0.30 to 6.37 μL mL⁻¹ (contact) and 0.029–0.037 μL mL⁻¹ (fumigation). The EO and its nanoemulsion were effective repellents against the Viçosa population at LC₅₀ and LC₇₀ levels across all exposure times. For the Sete Lagoas population, repellency was also observed, except for LC₅₀ at 4, 6, and 8 h, and LC₇₀ after 24 h. Increasing nanoemulsion concentrations reduced reproductive index (ri) and grain consumption in both populations. Population decline (ri < 0) began at 50.15 μL kg⁻¹ (Viçosa) and 67.29 μL kg⁻¹ (Sete Lagoas). These results highlight the potential of P. cablin EO for managing S. zeamais in stored grain.