Essential Oil-Based Nano-Biopesticides: Formulation and Bioactivity against the Confused Flour Beetle Tribolium confusum

Post-harvest pest control can rely on few approved pesticides and tools; hence, there is a rising interest in new sustainable, eco-friendly approaches. In this study, eight commercial essential oils (EOs) (anise Pimpinella anisum, artemisia Artemisia vulgaris, fennel Foenicum vulgare, garlic Allium sativum, lavender Lavandula angustifolia, mint Mentha piperita, rosemary Rosmarinus officinalis, and sage Salvia officinalis) were selected for their bioactivity and commercial availability, and then formulated in nano-emulsions. Repellency and acute toxicity of the developed nano-formulations were tested against a key stored product pest, Tribolium confusum (Coleoptera: Tenebrionidae). All the developed nano-emulsions presented optimal physical characteristics (droplet dimension = 95.01–144.30 nm; PDI = 0.146–0.248). All the formulations were repellent over time tested against adult beetles, in area preference bioassays. The best repellent was the anise EO-based formulation (RC50 = 0.033 mg). Mortality values from cold aerosol trials showed that the majority of tested EOs caused immediate acute toxicity, and garlic EO nano-emulsion caused the highest mortality of T. confusum adults (LC50 = 0.486 mg/L of air). EO-based nano-insecticides, used as cold aerosol and gel, are promising control methods against stored product pests, which can be integrated and combined with other sustainable biorational approaches.

Behavioral and Antennal Responses of Tribolium confusum to Varronia globosa Essential Oil and Its Main Constituents: Perspective for Their Use as Repellent

Essential oils of aromatic plants represent an alternative to classical pest control with synthetic chemicals. They are especially promising for the alternative control of stored product pest insects. Here, we tested behavioral and electrophysiological responses of the stored product pest Tribolium confusum, to the essential oil of a Brazilian indigenous plant, Varronia globosa, collected in the Caatinga ecosystem. We analyzed the essential oil by GC-MS, tested the effects of the entire oil and its major components on the behavior of individual beetles in a four-way olfactometer, and investigated responses to these stimuli in electroantennogram recordings (EAG). We could identify 25 constituents in the essential oil of V. globosa, with anethole, caryophyllene and spathulenole as main components. The oil and its main component anethole had repellent effects already at low doses, whereas caryophyllene had only a repellent effect at a high dose. In addition, the essential oil abolished the attractive effect of the T. confusum aggregation pheromone. EAG recordings revealed dose-dependent responses to the individual components and increasing responses to the blend and even more to the entire oil. Our study reveals the potential of anethole and the essential oil of V. globosa in the management of stored product pests.

Influence of Synthetic Flavorings on the Migration Activity of Tribolium confusum and Sitophilus granarius

Flavorings and volatile biologically active substances, used by humans for various purposes, may potentially have fumigating, repellent, or attractive effects on various species of anthropod storage pests. Tribolium confusum Jacquelin du Val, 1863 (Tenebrionidae) and Sitophilus granarius (Linnaeus, 1758) (Curculionidae) are the two most abundant pests of grain and grain products; the damage they cause to stored products of horticulture is 5–20% of the total yield of grain crops. In the experiment, we video-recorded migratory activity of beetles and evaluated it according to standard time periods (10, 20, 30, 60, and 120 seconds after the start of the experiment). No reliable influence of the 15 tested flavoring substances (benzyl alcohol, benzoic acid, toluene, hydroquinone, phenethyl alcohol, pinene, methylparaben, kojic acid, formic acid, isoamyl alcohol, tartaric acid, glycine, succinic acid, stearic acid, and ethylenediaminetetraacetic acid) on moving activity of Tribolium confusum was found. Exposure to benzyl alcohol brought a reliable decrease in locomotor activity of Sitophilus granarius (it exerted an attractant effect on imagoes as compared with the variant of the experiment without aromatic substances): 6.09 times more imagoes of S. granarius remained at a minimal distance from the aroma source than in the control, 6.07 more while exposed to hydroquinone, 5.50 to phenethyl alcohol, 4.50 to glycine, 3.44 to EDTA, 3.30 to toluene, 3.18 to methylparaben, 2.84 to succinic acid, 2.65 to benzoic acid, and 2.15 more when exposed to formic acid compared with the control variant of the experiment. Other surveyed flavoring substances (benzyl alcohol, pinene, kojic acid, isoamyl alcohol, tartaric acid, and stearic acid) had no significant effect on migratory activity of imagoes of S. granarius. The results allow us to recommend benzyl alcohol, hydroquinone, phenethyl alcohol, and glycine as potential luring substances or components of multicomponent flavoring mixtures during the assessment of the number of S. granarius in grain storage and processing facilities.