Essential oils (EOs), from plants’ secondary metabolism, present bioactive compounds that may have insecticidal activity. Their use associated with parasitoid hymenoptera can be an alternative, however, little is known about the impact of EOs on the diamondback moth, Plutella xylostella and parasitoids. This work aimed to evaluate the effect of oils from Eucalyptus citriodora (EOEC) and Schinus terebinthifolius (EOST) (0.5% and 1%) on eggs and larvae of P. xylostella and on Trichogramma pretiosum. P. xylostella eggs were immersed in solutions containing EOs and in water (control). Treated cabbage leaf discs were offered to larvae. Eggs with EOs were offered to T. pretiosum females to evaluate parasitism and emergence. Already parasitized P. xylostella eggs were immersed in the treatments to observe the effect on the emergence of parasitoids. The survival of T. pretiosum adults exposed to EOs was recorded. The average number of inviable eggs was higher in treatments with EOs, ranging from 6.9 ± 1.31 to 13.0 ± 1.12 than in the control (3.5 ± 0.32) (p < 0.05). The average number of dead caterpillars was higher in treatments with EOs, ranging from 1.4 ± 0.24 to 2.2 ± 0.19 than in the control (0.1 ± 0.06) (p < 0.05) Leaf consumption in 48 h did not differ between the EOST treatment (0.05) (5.42%) and the control (9.7%). For the other treatments it was significantly lower: 3.8% (EOEC 0.5), 1.6 (EOEC 1), and 3.4 (EOST 1). Eggs treated with EOs prior to exposure to the parasitoid had lower parasitism rates than eggs that were already parasitized and subsequently treated with EOs. The mortality of adults exposed to EOs was 3% to 6%. The EOs of E. citriodora and S. terebinthifolius were toxic to eggs and larvae of P. xylostella, acted as feeding deterrents, and had minimal impact on parasitoids. As a result, they are promising for use in IPM.