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TUESDAY, Dec. 6, 2016 (HealthDay News) -- New research hints at why the number of mosquitoes has jumped 10-fold in the past 50 years in certain U.S. states: Increased urbanization and shrinking levels of the pesticide DDT in the environment could be major factors.
"At first glance, recent increases in mosquito populations appear to be linked to rising temperatures from climate change, but careful analyses of data over the past century show that it's actually recovery from the effects of DDT," said study co-author Marm Kilpatrick. He is an associate professor of ecology and evolutionary biology at the University of California, Santa Cruz.
Still, Kilpatrick said, climate change may be a factor going forward.
"On the cold edge of a species' distribution, temperature matters a lot. In Washington, D.C., for example, where Aedes aegypti is not common now, it might become more common if the winters get milder," Kilpatrick said in a university news release.
Apart from the mere annoyance of mosquito bites, the insects can carry numerous diseases and viruses. The A. aegypti mosquito is considered the main culprit in spreading the Zika virus, which is believed to have caused thousands of devastating birth defects in babies, mainly in Brazil. The most common birth defect seen since the outbreak began in April 2015 is microcephaly, where the infant's head is too small and its brain is underdeveloped.
Kilpatrick's team based its findings on an analysis of mosquito-monitoring programs.
Why might urbanization -- which the study linked to mosquito levels in New Jersey and California -- be a factor?
The study authors suggested that it could boost the number of mosquitoes that feed on humans because there are more people around to bite.
As for DDT, which was commonly used through the early 1970s until it was banned, levels of the pesticide appeared to stick around.
"Everyone knew DDT was an extremely effective insecticide, but I was surprised by how long-lasting its effects were. In some areas, it took 30 to 40 years for mosquito populations to recover," Kilpatrick said.
The study was published in the Dec. 6 issue of the journal Nature Communications.
-- Randy Dotinga
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