Background: Compatibility of entomopathogenic nematodes (EPNs) with insecticides is a crucial mainstay of inte‑ grated pest management (IPM) programs. This study was designed to evaluate the joint action of EPN species and insecticides when employed to deter 3rd and 4th larval instars of cabbage white butterfy, Pieris rapaeL. (Lepidoptera: Pieridae) under laboratory conditions. EPNs [Steinernema carpocapsae(All strain), S. feltiae(Filipjev), Heterorhabditis bacteriophora(HP88), and H. bacteriophora(Ar‑4)], at concentrations of 50, 100, and 125 IJs/larva, were tested with 3 insecticides (lambda‑cyhalothrin, emamectin benzoate, and indoxacarb) at LC 25 and LC 50 values. Additionally, expression profles of 2 detoxifcation genes (CYP6AE120 and PrGSTs1) when the 4th instar larvae were treated by H. bacteriophora(HP88) and lambda‑cyhalothrin were examined. Results: Data indicated that statistically signifcant mortality of 2 larval instars of P. rapaewas observed in vitro among EPN species and pesticide concentrations. At concentration of 50 IJs/larva, LT 50 values were 2.385 and 3.92 days for S. carpocapsae(All strain) and H. bacteriophora(Ar‑4), respectively, on 3rd instar larvae; also, these values were 3.506 and 3.107 days for S. feltiaeand H. bacteriophora(Ar‑4), respectively, on 4th instar larvae Lambda‑cyhalo‑ thrin was the most toxic insecticide, followed by emamectin benzoate and indoxacarb at LC 25 and LC 50 , respectively. An additive efect was observed between EPN species with LC 25 and LC 50 of the tested insecticides, except for lambda‑cyhalothrin at LC 50 with H. bacteriophora(Ar‑4), and indoxacarb, with all EPNs showing antagonistic efects on mortality of 3rd instar larvae after 3 days post‑treatment. The interaction between the tested pesticides at LC 25 and LC 50 and EPN species, showed an additive efect, excluding lambda‑cyhalothrin at LC 25 with S. carpocapsae(All strain) and LC 25 of indoxacarb with H. bacteriophora(Ar‑4), which showed potentiation efects. The interaction of S. feltiae(Fil‑ ipjev) with tested insecticides at LC 50 exhibited an antagonistic efect on the mortality of 4th instar P. rapaelarvae after 3 days post‑treatment. The expression of both CYP6AE120 and PrGSTs1 was signifcantly up‑regulated with lambda‑ cyhalothrin, followed by H. bacteriophora(HP88) compared to control. Conclusions: The fndings suggested that combining EPNs and the pesticide concentrations can be a practical strategy for managing P. rapaeand could pave the way to using new control technologies in protecting organic farm vegetables from lepidopteran pests