Effect of grain mass on insecticidal activity of rosemary essential oil against storage beetles

Abstract: The use of essential oils (EOs) as fumigants for treating stored commodities is
hindered by their varying efficacy on different pest species. Another challenge in using EOs
practically is maintaining a sufficiently high concentration and understanding how the
commodity affects EO efficacy. In this study, we examined rosemary (Rosmarinus officinalis)
oil through laboratory tests to assess its fumigant toxicity on adults of two storage beetle
species, Sitophilus oryzae and Tribolium confusum, both with and without grain (wheat).
Results revealed that R. officinalis oil was toxic to both S. oryzae and T. confusum, with similar mortality rates of both species. However, the efficacy of the oil was significantly reduced in the presence of wheat grain. Specifically, the LC50 and LC99 values increased by approximately 1.5 to 4 times when the grain was present compared to treatment without the grain. Our results indicate that rosemary oil can be used as a fumigant for treating bulk grain in practice, but its reduced efficacy in bulk grain must be taken into account.