Apiaceae essential oil nanoemulsions as effective wheat protectants against five arthropod pests

The essential oils (EOs) produced by a number of Apiaceae species are well known for their insecticidal efficacy against a wide spectrum of insects, including vectors, stored product and agricultural pests. In the real world, rawly formulated EOs are scarcely effective due to their low chemical stability, limited persistence into the environment, and poor hydrophilicity. Therefore, for practical applications they need to be encapsulated using nanocarriers. In the present study, we evaluated two novel EO-based nanoemulsions (NEs), derived from Pimpinella anisum and Trachyspermun ammi, two plants with documented insecticidal effectiveness, for the management of stored product insects causing economic damages, including Tribolium castaneum, Tribolium confusum, Tenebrio molitor, Trogoderma granarium adults or larvae, and Acarus siro adults or nymphs. The NEs were prepared by a high-pressure homogenization procedure and determined according to the distribution of particle size through dynamic light scattering. Pimpinella anisum EO resulted mainly dominated by the phenylpropanoid (E)-anethole and other minor compounds, while T. ammi EO was mainly composed of thymol, p-cymene, and γ-terpinene and other minor constituents. Each EO-based NE was tested at two concentrations (500 and 1000 ppm) on stored wheat. We evaluated mortality values of the arthropod pests after 4 h, 8 h, and 16 h, and daily from 1–7 days. Complete mortality was achieved for T. castaneum larvae on wheat sprayed with 1000 ppm of 4% (w/w) P. anisum EO-based NE after 6 days of exposure. Similarly, the 8% (w/w) T. ammi EO-based NE killed 100.0% of the tested T. confusum larvae after 7 days to 1000 ppm. When A. siro adults was exposed to 1000 ppm of the 8% (w/w) T. ammi EO-based NE, 89.4% of the tested individuals were killed after 7 days. Binary EO-based NE combination toxicity tests were also carried out. Almost all T. molitor adults (97.8%) died after 7 days to 1000 ppm of 3% (w/w) T. ammi + 3% (w/w) P. anisum EO-based NE. The 3% (w/w) T. ammi + 3% (w/w) P. anisum EO-based NE killed 98.6% of T. granarium adults after 7 days at 1000 ppm. Overall, the tested Apiaceae EO-based NEs exhibited relevant pesticidal efficacy under short exposure intervals, therefore they could be taken into account as auxiliary management tools towards the sustainable protection of durable commodities in storages.