Pimpinella anisum essential oil nanoemulsions against Tribolium castaneum - Insecticidal activity and mode of action

The red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae), is an economically important pest of stored products. As possible alternative to conventional insecticides for its management, plant essential oils have gained interest owing to their effectiveness and eco-friendly features. However, they also show some drawbacks such as low stability, poor water solubility and diffusion, and limited persistence in the environment. A good strategy to overcome these disadvantages is represented by green nanotechnologies. Herein, we developed a nanoemulsion based on the essential oil from Pimpinella anisum L. (Apiaceae) containing 81.2% of (E)-anethole and evaluated its toxicity on T. castaneum adults and F1 progeny, as well as its morphological and histological impact. The anise oil nanoemulsion was characterized by the formation of a semi-solid interphase between oil and water, mean drop size was 198.9 nm, PDI was 0.303, zeta potential was -25.4±4.47 mV and conductivity was 0.029 mS/cm. The nanoemulsion showed toxicity on T. castaneum (LC50=9.3% v/v), with a significant impact on its progeny. Histological damages triggered by feeding and exposure to the anise nanoemulsion were also analyzed by scan electron microscopy (SEM). Overall, our findings showed that the development of nanoemulsions allows to improve the stability of P. anisum essential oil enhancing its efficacy against stored grain pests and contributing to reduce the use of harmful synthetic insecticides.