Perchlorate and hexavalent chromium are both significant anthropogenic pollutants in many areas of the world. Furthermore, these pollutants are often found in surface water where mosquitoes breed. Using Culex quinqufaciatus, a common vector of encephalitis, we tested the hypothesis that perchlorate, hexavalent chromium, or the combination of pollutants, would interact with control strategies for mosquito larvae based on the bacteria Bacillus thuringiensis var. israelensis (Bti). Significantly more Bti (56%) was required for control when perchlorate was removed from the system. Similarly, when Chromium was removed from the system, significantly (77%) more Bti was required for control. The implications of this research for both ecosystem health and mosquito control are substantial.