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 F progeny, as well as its morphological and histological impact. The aniseed 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 (LC = 9.3% v/v), with a significant impact on its progeny. Morphological and histological damages triggered by feeding and exposure to the aniseed nanoemulsion were analyzed by scanning electron microscopy (SEM) and light microscopy. 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.

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Three essential oils extracted from German chamomile, Matricaria chamomilla, Anise, Pimpinella anisum and cumin, Cuminum cyminum were assessed against two of the major stored grain insect species, Sitophilus oryzae (L.) and Tribolium castaneum (Herbst). The chemical composition of the essential oils was determined by gas chromatography (GC) and GC/mass spectrometry. The bioactivity of the oils determined was assessed against both species. A concentration of 100000 ppm, essential oils caused 100% mortality of S.oryzae after 96 h. of exposure, whereas, T. castaneum were more tolerant to the oils than S. oryzae. At this concentration, the values of F 1 progeny production, progeny reduction (%) and grain weight loss (%) of both insect species were lower than other concentrations. Eventually, all oils exhibited a negative impact on some biological aspects of both insects. These results highlight the potential of these oils as grain protectants and antifeedants, and consequently could be suitable for the management of insect pests in grain stores.

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