The Role of Tire Leachate in Condition-Specific Competition and the Persistence of a Resident Mosquito from a Competitively Superior Invader

SIMPLE SUMMARY: Condition-specific competition is when the outcome of competition varies with environmental conditions. Tradeoffs between species’ competitive abilities and tolerances to adverse conditions are common and can facilitate or inhibit insect invasions and their impacts. Many studies have shown that the resident mosquito Culex pipiens persists with the competitively superior invasive mosquito Aedes albopictus in urban areas of the United States. Discarded vehicle tires are common developmental aquatic habitat for these species and degrade when exposed to ultraviolet (UV)-B light to release a suite of contaminants. We tested the hypothesis that more highly degraded tires that contain greater amounts of contaminants produce a condition-specific advantage for Cx. pipiens by altering the outcome of competition with Ae. albopictus. We found stronger competitive effects of Cx. pipiens on the population performance and survival of Ae. albopictus in tires exposed to shade and full-sun conditions that had higher concentrations of tire leachate than no UV-B conditions. This suggests that increased tire degradation and tire leachate promotes condition-specific competition and facilitates the regional persistence of Cx. pipiens after the invasion of Ae. albopictus. ABSTRACT: (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, Culex pipiens, by altering the outcome of competition with the competitively superior invasive Aedes albopictus. (2) Methods: In a competition trial, varying densities of newly hatched Ae. albopictus and Cx. pipiens 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 Cx. pipiens and Ae. albopictus 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 Cx. pipiens on the population performance and survival of Ae. albopictus in tires exposed to shade and full-sun conditions that had higher concentrations of contaminants. Further, zinc concentration was higher in emergent adults of Ae. albopictus than Cx. pipiens. 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 Ae. albopictus over resident Cx. pipiens and, combined with Cx. pipiens’ preferential oviposition in higher resource sites, contribute to the persistence of the resident species.