This study aimed to evaluate the synergy and response homogeneity of the Spodoptera frugiperda larvae population to the essential oil of Piper aduncum in combination with insecticides formulated with two active ingredients in ready mixtures: Imidacloprid/beta-Cyfluthrin, Teflubenzuron/ alpha-Cypermethrin and Thiamethoxam/lambda-Cyhalothrin, compared with piperonyl butoxide (PBO positive controls).By the ratio of the LC 50 and LD 50 of the insecticides taken singly and their respective synergistic combinations with essential oil and (PBO), the synergism (FS) factors for comparison with each other were obtained.The slope of the dose/concentration-mortality curves was used to determine the relative toxicity promoted by synergistics and the homogeneity of response.Residual contact revealed a significant potentiation for commercial insecticides formulated with ready mixtures Thiamethoxam/lambda-Cyhalothrin ) and Teflubenzuron/alpha-Cypermethrin (FS= 968.3 -1294.4),when combined with the essential oil of P. aduncum.In the topical contact, there were significant potentiation only for the ready mixtures of Teflubenzuron/alpha-Cypermethrin ) insecticides when combined with essential oil.The synergistic combinations presented homogeneous response by topical contact as well as residual, for at least a synergistic combination with essential oil of P. aduncum.The FS significance values of combinations of the P. aduncum essential oil with ready mixtures insecticides Thiamethoxam/lambda-Cyhalothrin and Teflubenzuron/alpha-Cypermethrin, may indicate this essential oil as an alternative to PBO for synergistic effect.