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Vector-borne diseases pose a severe threat to human and animal health. <i>Culex pipiens</i> L. (Diptera: Culicidae) is a widespread mosquito species and serves as a vector for the transmission of infectious diseases such as West Nile disease and Lymphatic Filariasis. Synthetic insecticides have been the prime control method for many years to suppress <i>Cx. pipiens</i> populations. However, recently, the use of insecticides has begun to be questioned due to the detrimental impact on human health and the natural environment. Therefore, many authorities urge the development of eco-friendly control methods that are nontoxic to humans. The bacterial associates [<i>Xenorhabdus</i> and <i>Photorhabdus</i> spp. (Enterobacterales: Morganellaceae)] of entomopathogenic nematodes (EPNs) (<i>Sterinernema</i> spp. and <i>Heterorhabditis</i> spp.) (Rhabditida: Heterorhabditidae and Steinernematidae) are one of the green approaches to combat a variety of insect pests. In the present study, the mosquitocidal activity of the cell-free supernatants and cell suspension (4 × 10⁷ cells mL⁻¹) of four different symbiotic bacteria (<i>Xenorhabdus nematophila</i>, <i>X. bovienii</i>, <i>X. budapestensis</i>, and <i>P. luminescens</i> subsp. <i>kayaii</i>) was assessed against different development stages of <i>Cx. pipiens</i> (The 1st/2nd and 3rd/4th instar larvae and pupa) under laboratory conditions. The bacterial symbionts were able to kill all the development stages with varying levels of mortality. The 1st/2nd instar larvae exhibited the highest susceptibility to the cell-free supernatants and cell suspensions of symbiotic bacteria and the efficacy of the cell-free supernatants and cell suspensions gradually declined with increasing phases of growth. The highest effectiveness was achieved by the <i>X. bovienii</i> KCS-4S strain inducing 95% mortality to the 1st/2nd instar larvae. The results indicate that tested bacterial symbionts have great potential as an eco-friendly alternative to insecticides.