Mosquitoes in sewage-contaminated streams grow bigger and faster than those in purer waters, find a new study.
According to a report in Discovery News, over a 16-week study period last summer, Luis Fernando Chaves, an ecologist at Emory University in Atlanta and colleagues sampled water quality and mosquito larvae from two streams, one that receives contaminated overflows and one that doesn't, in the Atlanta area.
In every sample they collected from the contaminated stream, they found mosquito larvae. In a clean stream, on the other hand, larvae showed up less than 10 percent of the time.
In a follow-up experiment, the researchers grew mosquitoes in containers that held either normal tap water or polluted water.
The polluted tanks were full of ammonia phosphates, which are abundant in sewage and are known to feed the bacteria and microorganisms that mosquitoes eat.
The experiment showed that the mosquitoes that had access to that sewage-nutrient richness hatched from their eggs more quickly, were more likely to survive and grew to be larger than the pollution-free mosquitoes.
Besides having more to eat in polluted streams, mosquitoes also have less to worry about, according to Chaves.
Mosquitoes breed in water, but they breathe air, while the fish that eat them can't survive in the sewage-tainted water.
An earlier study by the Centers for Disease Control and Prevention found that bigger floods led to more mosquitoes, particularly Southern house mosquitoes, which are a known carrier of West Nile virus.
The latest research helps explain why.
"We've known for a while that it's likely that these combined sewage overflows were creating not only a mosquito problem but a West Nile problem," said Rosmarie Kelly, a public health entomologist at the Georgia Department of Community Health in Atlanta.
The new work is "adding to this knowledge."
"What it means for people is that we need to push to have cleaner streams in cities," study lead author Luis Fernando Chaves, an ecologist at Emory University in Atlanta, told Discovery News.
"One way to reduce these artificial problems is to ensure the water quality of these streams by not dumping sewage in them," he added.
According to Kelly, the best way for people to protect themselves and their neighbors is to wear bug repellent and dump out any reservoirs of standing water in their yards.