| Summary: | (1) Background: Condition-specific competition, when the outcome of competition varies with abiotic conditions, can facilitate species coexistence in spatially or temporally variable environments. Discarded vehicle tires degrade to leach contaminants into collected rainwater that provide habitats for competing mosquito species. We tested the hypothesis that more highly degraded tires that contain greater tire leachate alters interspecific mosquito competition to produce a condition-specific advantage for the resident, <i>Culex pipiens</i>, by altering the outcome of competition with the competitively superior invasive <i>Aedes albopictus</i>. (2) Methods: In a competition trial, varying densities of newly hatched <i>Ae. albopictus</i> and <i>Cx. pipiens</i> larvae were added to tires that had been exposed to three different ultraviolet (UV)-B conditions that mimicked full-sun, shade, or no UV-B conditions in the field. We also measured <i>Cx. pipiens</i> and <i>Ae. albopictus</i> oviposition preference among four treatments with varying tire leachate (high and low) and resources (high and low) amounts to determine if adult gravid females avoided habitats with higher tire leachate. (3) Results: We found stronger competitive effects of <i>Cx. pipiens</i> on the population performance and survival of <i>Ae. albopictus</i> in tires exposed to shade and full-sun conditions that had higher concentrations of contaminants. Further, zinc concentration was higher in emergent adults of <i>Ae. albopictus</i> than <i>Cx. pipiens</i>. Oviposition by these species was similar between tire leachate treatments but not by resource amount. (4) Conclusions: These results suggest that degraded tires with higher tire leachate may promote condition-specific competition by reducing the competitive advantage of invasive <i>Ae. albopictus</i> over resident <i>Cx. pipiens</i> and, combined with <i>Cx. pipiens’</i> preferential oviposition in higher resource sites, contribute to the persistence of the resident species.
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