Synergistic Efficacy of Plant Essential Oils with Cypermethrin and Chlorpyrifos Against Spodoptera littoralis, Field Populations in Egypt

Background: The essential oils of the plant synergize the synthetic chemical pesticide activity against pests. Controlling pests mainly with synthetic chemical pesticides causes the resistance to build up in these pests like S. littoralis. Methods: This study was conducted to evaluate the synergistic effect of garlic and thymol oils with cypermethrin and chlorpyrifos on field populations of S. littoralis. Also, the impact of the mixtures on activities of three enzymes: Glutathione Stransferase (GST), general esterase (άβEST) and mixed function oxidase (MFO) of S. littoralis using dipping technique. Results: Bioassay shows elevated LC50 for each of cypermethrin and chlorpyrifos alone. Whereas, the toxicity of cypermethrin and chlorpyrifos were synergized 2.81 to 9fold; 2.74 to 8.35fold by garlic oil respectively, but far less synergism occurred with thymol oil. The analysis showed the GST, άβEST and MFO were notably inhibited by garlic and thymol oils synergism with cypermethrin and chlorpyrifos in S. littoralis. Conclusions: The results concluded that inhibition of the enzymes could be the result of the synergist of the essential oils when it mixed with synthetic insecticides to control S. littoralis in the field.