Insecticidal activity of rosemary essential oil against primary and secondary storage beetles in the presence and absence of grain

Abstract

Rosemary oil, an essential oil (EO) isolated from Rosmarinus officinalis (Lamiaceae), possesses unique properties, functioning both as a food additive and an insecticidal agent. However, the application of EOs, including rosemary oil, as fumigants for stored commodities faces challenges due to their varying efficacy across pest species and the influence of stored grain on EO performance. This study examined the fumigant toxicity of rosemary oil on adults of various storage beetle species, including primary (Rhyzopertha dominica, Sitophilus granarius, S. oryzae) and secondary pests (Oryzaephilus surinamensis, Tribolium confusum), under conditions with and without wheat kernels. The results revealed significant species-specific differences in susceptibility, with O. surinamensis and R. dominica being more sensitive (LC₅₀ values of 9.82 and 16.07 μlL⁻¹, respectively) compared to S. oryzae, S. granarius, and T. confusum (LC₅₀ values of 45.19, 46.44, and 47.74 μlL⁻¹, respectively). The presence of wheat significantly reduced EO efficacy, with declines ranging from 1.5 to 4 times, depending on the species. Notably, this work newly revealed that the tested secondary pests (O. surinamensis and T. confusum) exhibited a greater decrease in efficacy in the presence of grain compared to the primary pests. These findings suggest that while rosemary EO shows potential as a fumigant for grain storage, species-specific sensitivity and reduced efficacy in grain-filled environments, particularly for secondary pests, warrant further investigation.