Efficacy of pulegone, and eugenol alone and in combination with synthetic insecticides for the management of three stored product beetle pests

The rising public concern over the safety and environmental impact of synthetic insecticides, along with the evolution of resistance, are driving entomologists to search for new pest control alternatives. Essential oils and their constituents have been proposed as the most promising alternatives due to their wide spectrum of biological activity and synergistic interaction with traditional insecticides. Therefore, the present work evaluated the toxicity of a monoterpene, pulegone (250 and 500 mg/kg), and a phenylpropene, eugenol (250 and 500 mg/kg), alone and in combination with deltamethrin (0.1 and 0.25 mg/kg), pirimiphos-methyl (2.5 and 5.0 mg/kg), and thiamethoxam (0.1 and 0.5 mg/kg) against Rhyzopertha dominica, Sitophilus oryzae, and Tribolium castaneum on wheat grains. Pulegone exerted significant toxicity at 250 and 500 mg/kg against the three beetle species, with complete mortality after 14 days of exposure, complete inhibition of progeny production, and complete protection of treated wheat grain after 75 days of treatment. While eugenol at the higher application rate tested (500 mg/kg) caused 68.3, 31.7, and 5.0 % mortality in adults of R. dominica, S. oryzae, and T. castaneum, with reduction in progeny production of 81.3, 67.7, and 79.7%, respectively. In combination treatments, pulegone reduced toxicity against tested insect species when mixed with the three insecticides, indicating an antagonistic effect. While treated wheat grains with binary mixtures of eugenol (500 mg/kg) with deltamethrin, pirimiphos-methyl, and thiamethoxam enhanced their toxicity, resulting in higher mortality rates, fewer emerged adults, and a lower loss in weight of wheat grains than those obtained in individual treatments. Based on these findings, we suggest that pulegone and eugenol might be viable options for usage in protecting stored wheat against the tested insect species. Additionally, eugenol has the potential to enhance the toxicity of synthetic insecticides, which could reduce their application rates and manage the resistance to these insecticides. •Pulegone showed significant toxicity against all insect species, giving complete mortality, full inhibition of progeny production, and complete protection of treated wheat.•Eugenol enhanced the toxicity against the three insect species when combined with deltamethrin, pirimiphos-methyl, and thiamethoxam.•Pulegone exhibited an antagonistic effect when mixed with the three synthetic insecticides.