Aphis gossypii Glöver is one of the main cotton insect pests, causing significant losses in the crop. In order to reduce these damages, frequent applications of insecticides are carried out, despite reported cases of resistance. One auxiliary tool of resistance management is the combination of natural and synthetic products because the combinations can deliver comparable or greater pest toxicity while reducing the necessary dose of the synthetic molecules, thus maintaining its effectiveness. Therefore, the present work evaluated the toxicity of Ocimum basilicum essential oil, the synthetic insecticide thiamethoxam and the combination of these in the control of cotton aphid. The acute toxicities of thiamethoxam and the essential oil were obtained through dose response assays; then, combinations of the two products were assessed. The essential oil had a high concentration of linalool and it exhibited toxicity to the cotton aphid. The combination of the two products caused high mortality, particularly when they were applied as the LD 50 of the thiamethoxam + LD 50 of the essential oil and the 50% LD 50 of the thiamethoxam + 50% LD 50 of the essential oil. This work concludes that O. basilicum L. essential oil combined with thiamethoxam may be an alternative in the population management of the cotton aphid and may contribute in the future to the management of resistance and reduce the environmental impact of pesticides.