Toxicological Stability of Piper aduncum L. Essential Oil During Storage Against Stored-Product Insect Pests

Piper aduncum L. essential oil (PAEO) has insecticidal potential, but its performance under different storage conditions remains incompletely characterized. We compared PAEO stored at 5, 20, or 35 °C protected from light and, in a separate experiment at 20 °C, under light-protected or light-exposed conditions. Adults of four stored-product beetle species were tested after 4, 8, and 12 months. Initial GC-MS characterization showed that dillapiole accounted for 70.34% of the chromatographic area. Replicate-level mortality counts were analyzed using binomial-probit models. Assessment time was associated with concentration–mortality responses for all four species; the trajectories were species dependent and often non-monotonic. Exploratory within-assessment model comparisons generally showed higher median lethal concentrations for the bottles stored at 35 °C or exposed to light at 4 and 8 months, although these patterns differed by species. The storage experiments were not factorial. Each condition had one oil bottle, and differences between assessment dates cannot be attributed solely to oil aging because concurrent fresh-oil controls were unavailable. PAEO remained insecticidally active at each assessment, but chemical changes and their mechanisms were not tested longitudinally.