A critical step in managing adult mosquito populations is known as source reduction where the goal is to reduce or eliminate standing water conditions that mosquitoes need to lay their eggs. Some mosquito species prefer temporary water holding containers such as tree holes, plant pots, and even discarded tires to serve as these larval development sites. These mosquito species are often referred to as “container” mosquitoes and include species such as Aedes albopictus (Skuse) and Ae. aegypti (L.), both vectors of dengue, chikungunya, and Zika viruses. 

Combatting and removing illegally discarded tires is an important challenge for the city of New Orleans in the fight against dangerous mosquitos. Recent surveys showed that tire dumping in public rights of way has more than doubling from 2010 to 2018. And, more tires mean more mosquito development sites. In fact, a previous discarded tire survey logged over 1,000 used tires throughout the city, with more than half of those tires occupied by mosquito larvae. Eliminating these tires to reduce mosquito development sites is critical to managing the mosquito problem, but this has proved to be a challenge for several reasons including a lack of awareness concerning the link between tires and mosquitoes among residents, and locating discarded tires for removal.  

To help the City of New Orleans tackle this issue, researchers surveyed tire piles and adult mosquitoes across 12 sampling sites in the city between May and October of 2020. Their goal was to better understand where and why tires were likely to be found in the city, as well as what mosquito species were more likely to be found in these areas with discarded tires. They hypothesized that tire distribution across the city would be linked to median income and vacancy of residences. In other words, they suspected that tires were more likely to be found in lower income neighborhoods with more abandoned homes that would serve as dumping grounds. To address these questions, researchers looked at many factors including median income, population density, tire counts, and heat severity.  

They also predicted that mosquito species distribution would differ in areas with a high tire density. To investigate this theory, they needed to look at data that could give them more information on a smaller scale. Variables such as rainfall and temperature were generally good factors used to predict mosquito distribution, but in this case both factors were likely to be relatively uniform across the city and therefore may not offer much help when trying to understand differences between neighborhoods. However, vegetation cover and urbanization across the city were more likely to differ from one neighborhood to the next. Another variable they wanted to consider was the condition known as the urban heat island effect where areas with more concrete and pavement absorb solar heat during the day and release it at night. This urban heat island effect combined with differences in vegetation could be creating microclimates that could influence mosquito species distribution across the city. For mosquito abundance and distribution, they focused on three species: Culex quinquefasciatus (Say) which is a vector for West Nile virus (WNV) and St. Louis encephalitis virus (SLE), as well as Ae. albopictus and Ae. aegypti.  

When researchers compared the mosquito collection data with urban heat island estimates and the various social factors, the data showed that tire abundance was in fact higher in low-income neighborhoods with lower population density. For mosquito species distribution, they found that Ae. albopictus were found in higher numbers in areas with higher tire abundance and a lower heat severity rating. For the other two species, Ae. aegypti were more abundant in areas of high heat and Cx. quinquefasciatus were more abundant in areas of low heat.  

To sum all of this up, their data showed that low-income areas with more abandoned homes in New Orleans were more likely to have discarded tires. And these areas with high tire density and low heat severity were also more likely to have higher populations of Ae. Albopictus, a medically important species. These findings give the City of New Orleans direction on where to prioritize source reduction efforts in the city, as well as offering more information to educate low-income communities on the risk posed by discarded tires as a potential exposure pathway for their communities.   

Article by: Mike Bentley, PhD, BCE

References

Rebeca de Jesús Crespo, Alexandros Pavlakis, Jennifer Breaux, Claudia Riegel, Discarded vehicle tires and their association with mosquito vector abundance across socioenvironmental gradients in New Orleans, LA, Journal of Medical Entomology, Volume 61, Issue 5, September 2024, Pages 1240–1250, https://doi.org/10.1093/jme/tjae092

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