The Culex pipiens complex is a major and prevalent pest of dipterans for the most part of the world. The addition of sub-lethal quantities of chemical toxicants, such as fungicides and herbicides, can change the toxicity of certain insecticides on mosquito larvae. Hence, the purpose of the current study was to evaluate toxicity of certain insecticides individually and in combination with the sub-lethal concentrations of myclobutanil (1 µg ml^-1) or S-metolachlor (0.140 µg ml^-1) against C. pipiens larvae after 24, 48 and 72 h of exposure. Depending on the combination of the sub-lethal concentrations of S-metolachlor and myclobutanil, as well as the LC₅₀ values of each studied insecticide, the insecticides exhibited distinct interaction reactions (e.g., antagonistic and/or synergistic effects) on C. pipiens larvae. Permethrin mixed with myclobutanil or S-metolachlor at sub-lethal concentrations produced a synergistic effect and enhanced permethrin's toxicity on C. pipiens larvae during exposure durations (except for the sub-lethal concentration of S-metolachlor after 72 h). On the other hand, following exposure times, combining imidacloprid or cyromazine with sub-lethal concentrations of myclobutanil or S-metolachlor was an antagonistic impact and reduced the toxicity of both insecticides on C. pipiens larvae. Only after 24 h of exposure did the sub-lethal concentrations of myclobutanil or S-metolachlor increase the lethality of indoxacarb; however, after 48 and 72 h of exposure, they decreased the toxicity of indoxacarb. It will be worthwhile to evaluate the impact of insecticides on fish and mosquito larvae when sub-lethal levels of herbicides and fungicides are present.