Toxicological Stability of Piper aduncum L. Essential Oil in the Control of Insect Pests of Stored Products

Piper aduncum L. essential oil (PAEO) contains bioactive compounds with acknowledged insecticidal potential against various agricultural pests. Nevertheless, there is limited information about its long-term toxicological stability. In this sense, this study sought to assess the toxicological stability of PAEO after storage for 12 months at different temperatures (5 °C, 20 °C, and 35 °C) and light conditions (exposed to light or not), focusing on four insect pest species of stored grains: Sitophilus zeamais (Coleoptera: Curculionidae), Tribolium castaneum (Coleoptera: Tenebrionidae), Oryzaephilus surinamensis (Coleoptera: Silvanidae), and Cryptolestes ferrugineus (Coleoptera: Cucujidae). The toxicological stability of PAEO was evaluated every four months using concentration-mortality bioassays. Dillapiole was the predominant constituent, representing 70.34% of the identified compounds. At the conclusion of the 12-month evaluation, the PAEO demonstrated increased toxicity to the species S. zeamais, O. surinamensis, and C. ferrugineus. High temperature (35 °C) and light exposure significantly reduced the toxicity of PAEO to all four species. In conclusion, the efficacy of PAEO against insect pests is best preserved when kept in amber bottles, at temperatures not exceeding 20 °C, and shielded from light.