Piperonyl butoxide synergizes the larvicidal activity of Origanum vulgare essential oil and its major constituents against the larvae of Aedes albopictus and Culex pipiens quinquefasciatus

•37 compounds were successfully identified from Origanum vulgare essential oil.•O. vulgare EO were toxic to Aedes albopictus and Culex pipiens quinquefasciatus.•O. vulgare EO’s major compounds thymol and carvacrol were toxic to mosquito.•Piperonyl butoxide improved the toxicity of O. vulgare EO, thymol and carvacrol.