Sensory quality of essential oils and their synergistic effect with diatomaceous earth, for the control of stored grain insects

Essential oils (EOs) have gained increasing interest as a low-toxic, eco-friendly alternative to synthetic repellents and insecticides against insect pests. However, they have scarce practical application in the protection of stored grain because of their limited efficacy and their interference with the organoleptic properties of the grain. In this study, we evaluated the olfactory profile of the EOs of Foeniculum vulgare, Pistacia lentiscus, and Ocimum basilicum, and their toxicity against the main stored grain pest Sitophilus granarius. Trained assessors identified O. basilicum and F. vulgare, as more suitable than the P. lentiscus EO for the wheat treatment. In laboratory tests, the most toxic EO was the P. lentiscus (LC₅₀ = 36.36 μL·kg^-1) while, the least toxic, was the F. vulgare one (LC₅₀ = 77.59 μL·kg^-1). The EOs were also tested combined with diatomaceous earths (DEs) showing synergistic effects (co-toxicity coefficient values ranging from 1.36 to 3.35 for O. basilicum and F. vulgare EOs, respectively). Overall, O. basilicum resulted as the best EO for the wheat treatment, considering its insect toxicity and olfactory profile. In real storage conditions, the wheat co-treated with O. basilicum EO and DEs showed a significantly lower mean infestation (1.5 insect kg^-1) than the non-treated wheat (7.0 insect kg^-1).