The effects of UV radiation on tire deterioration and pollutant release on competition between Aedes albopictus and Culex pipiens mosquitoes

Background/Question/Methods

Although recycling programs have reduced stockpiles of scrap tires in the US, vast numbers of tires are still deposited throughout landscapes nationwide. In Maryland, over 5.5 million disused tires require proper disposal each year. Many scrap tires are illegally dumped in peridomestic areas. Among the most important environmental impacts from tires is their degradation when exposed to ultraviolet (UV) radiation, and the resultant leaching of numerous soluble inorganic (e.g., in particular, zinc) and organic contaminants. Studies have shown clear toxicological effects of tire leachate on a few focal aquatic taxa, but there is a lack of knowledge on the effects of tire leachate on the most aquatic communities. This project investigates the relationship of scrap tire contamination on the ecologies of the invasive mosquito Aedes albopictus and the co-occurring resident mosquito Culex pipiens. A. albopictus competes for microbial food with the C. pipiens in water-holding containers throughout urban and rural landscapes. Specific objectives of this project were to: (1) Examine tire degradation under different UV radiation treatments in the laboratory (full sun, shade, and  no UV conditions); (2) Assess effects of UV radiation on microbial growth and larvae development through metabolic rate measurements.  

Results/Conclusions

Discarded tires exposed to full sun conditions leached higher zinc concentrations than tires exposed to shade and no UV conditions, after 150 days of exposure to treatments. Both, A. albopictus and C. pipiens larval metabolic rates were higher under full sun conditions than shade and no UV conditions.  Metabolic rate of microbial communities is greater under no UV conditions, and lowest under full sun conditions. These findings suggest that larvae of both species are likely expending higher energy browsing food resources, development, and maintenance under full sun conditions.  Survival for both species were lowest under full sun than shade and no UV conditions, and A. albopictus had consistently higher survival than C. pipiens across all UV conditions. These results show clear effects of UV conditions on tire deteriation, microbial production, and mosquito larval development and survival. Because A. albopictus and C. pipiens often co-occur in the same individual tire habitat and compete for microbial resources, tires provide ideal model systems for testing the effects of a habitat gradient (environmental toxin) on the outcome of competition. Ongoing experiments are testing of the effects of tire degradation, under different UV conditions, on interspecific resource competition between A. albopictus and C. pipiens.