Biotoxicity of essential oils and their nano-emulsions against the coleopteran stored product insect pests Sitophilus oryzae L. and Tribolium castaneum herbst

Abstract

The insecticidal activity of anise, thyme, and coriander essential oils in bulk and prepared nano-emulsions formulations were evaluated against the adults of stored grain pests Sitophilus oryzae and Tribolium castaneum. The prepared essential oil nano-emulsions exhibited poly dispersity indices ranging from 0.209 to 0.37, and zeta potentials between −14.5 and −27.8 mV. The smallest oil nano-emulsion droplet diameter was coriander (88.83 nm) and the largest was anise (103.57 nm). Although no significant differences in the toxicity of the three oils against T. castaneum were detected, anise and thyme oils were significantly more toxic than coriander oil to S. oryzae. Preparing the anise and thyme oils as nano-emulsion formulations significantly increased the toxicity by 1.50- and 1.47-fold, respectively, against T. castaneum. The nano-emulsions were also significantly more toxic (1.41–1.48 times) than the bulk essential oils to S. oryzae. The anise nano-emulsion showed the highest toxicity against S. oryzae and T. castaneum, with LC50 values of 3858.88 and 4985.1 mg/L respectively. GC–MS analysis of anise essential oil revealed that ultra-sonication caused a 2.73-fold decrease in the anethole level in the nano-emulsion and completely removed nine minor compounds. The anise oil nano-emulsion was the most effective insecticide, reducing S. oryzae emergence by 94.64% and protecting nearly 84.5% of wheat grains from T. castaneum infestation. Finally, the tested NEs or EO had not any negatively significant effect on wheat seed germination rate.