Sarah Rothman’s work suggests plants may play a role in higher West Nile virus exposure in low-income communities.
Picture escaping from the most dangerous animal in the world. Are you running from a grizzly bear, swimming from a shark, or hiding from some otherwise terrifying predator? You should be applying bug spray instead, because mosquitos transmit diseases that kill more humans than any predator on Earth.
Tragically, lower-income people face a greater risk of mosquito-borne illnesses than wealthier individuals. Studies at the University of Maryland Department of Environmental Science and Technology are unraveling the root causes of such inequity in urban environments.
Sarah Rothman, PhD candidate in the Department of Environmental Science and Technology recently won the UMD three-minute thesis research presentation award for her talk describing some of that work. Her video went on to represent UMD in the U21 3Minute Thesis (3MT) competition, which features work from 600 universities. You can see her video here.
“My research investigates how the distribution and density of different plant species on a city block play an important role in the abundance of mosquitos and West Nile Virus infection rates,” Rothman said. “I hope this work can give us insight for controlling mosquitos through vegetation, and hopefully address an environmental injustice for urban residents.”
Previous work by Rothman’s mentor, Professor Paul Leisnham, and his colleagues showed that mosquitos in Baltimore, MD, are more numerous and longer lived on blocks with more lower income residents, abandoned buildings and empty lots. Rothman found those mosquitos are also more likely to carry West Nile Virus, the most common mosquito-borne disease in the continental U.S.
More mosquitos with higher infection rates is a double whammy that means higher potential exposure to West Nile Virus for residents on lower-income blocks.
To understand how a city block’s socio-economics could influence mosquitos, Rothman turned to their source of food. Plants. Mosquito larvae feed on the microbes that form in standing water around dead and decaying leaves. Her surveys of Washington, DC and Baltimore City found that the most common plant species on low income blocks were non-native, while high-income blocks hosted mostly native species.
Previous laboratory studies showed that decaying non-native plants tend to support faster mosquito growth and larger adults than native plants. In addition, the two most common mosquito species in the region are more likely to co-exist among non-native plants. That has implications for disease transmission, because one mosquito plays a greater role in amplifying West Nile virus among birds, which spread the disease more widely, and the other is thought to play a greater role in transmitting it to humans.
Rothman’s work is the first to put all these pieces together and look at the influence of plant species on mosquito populations along socio-economic lines. She hypothesizes that the outsized abundance of non-native plants on low-income blocks compared to high-income blocks not only supports faster-growing, larger adults, but that this leads to a higher number of mosquitos of both species and contributes to inequitable West Nile Virus exposure.
Rothman’s next step will be to raise mosquitos in the lab on the plant species representative of the different blocks she surveyed to see how they influence mosquito development, size, longevity and overall population growth rate. Her work will give insight into how to control mosquitoes using vegetation.
“If we find a relationship between certain plants and high mosquito population growth, then we can focus on prevention and potential management by surveying areas for these plants and addressing the problem,” Rothman said. “Surveying for non-native plant species is easier and quicker than surveying for mosquito larvae, which can be small and difficult to find, allowing mosquito control agencies to target areas that are likely to have the greatest infestations in a more efficient manner.”
