MIAMI – Two more tropical disease-carrying mosquitoes have been found on the U.S. mainland for the first time, caught in traps near Florida's Everglades.
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The scientists involved say this could raise the risk of mosquito-borne viruses reaching people and birds, but health officials say it's too early to sound an alarm.
The new arrivals from Latin America and the Caribbean — Culex panocossa and Aedeomyia squamipennis — were trapped in October in rural areas bordering Everglades National Park by University of Florida Institute of Food and Agricultural Sciences entomologist Nathan Burkett-Cadena and Florida Medical Entomology Laboratory researcher Erik Blosser.
Their research is being published in the Journal of Medical Entomology and the journal Acta Tropica.
In the traps, they discovered that native species were crowded out by thousands of Culex panocossa mosquitoes and hundreds of Aedeomyia squamipennis mosquitoes.
Both species can be found on a few Caribbean islands as well as from Mexico into South America. They lay their eggs on water lettuce — invasive weeds that float in the canals, drainage ditches and other waterways crisscrossing Florida neighborhoods.
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"'Hundreds' is substantial, particularly when you get a hundred from a single trap. This is not a single specimen that blew in from a storm — this is a reproducing species," Burkett-Cadena said.
About 15 invasive mosquitoes now live in Florida, including nine that have arrived in the last decade. One, Aedes aegypti, is blamed for spreading the Zika virus, along with dengue fever and chikungunya.
The new arrivals are another sign that climate change, along with increased tourism and global trade, has made Florida more hospitable to exotic species, Burkett-Cadena said.
Health officials downplayed the immediate cause for concern, saying more research was needed.
"We have seen in Florida some invasive mosquito species that have become significant and others that have not," Florida Department of Health spokeswoman Mara Gambineri said in an email Tuesday.
One of roughly 200 mosquito species worldwide known to transmit diseases to humans, Culex panocossa can spread Venezuelan equine encephalitis, a family of viruses that includes the Everglades virus.
The native Florida mosquito Burkett-Cadena and Blosser were hoping to trap also can infect humans with Everglades virus, but it rarely has the opportunity to do so because humans rarely venture into its remote wetlands habitat.
The new Culex species in Florida lives closer to civilization, potentially increasing the risk of Everglades virus exposure, Burkett-Cadena said.
Aedeomyia squamipennis spreads bird malarias, including the kinds that have devastated Hawaii's native bird populations. These parasites already are found in Florida, but the introduction of a new carrier that feeds predominantly on birds could be worrisome for struggling Florida birds, Burkett-Cadena said.
Gambineri said many factors can determine whether a disease-carrying invasive species becomes a significant concern, such as its choice of host, its habitat, its tolerance of cooler temperatures and competition from other species.
Janet McAllister, a medical entomologist with the U.S. Centers for Disease Control and Prevention, said other species capable of transmitting Venezuelan equine encephalitis already live in the country. The most recent U.S. outbreak was in the 1970s, infecting humans and horses in Texas and Louisiana.
"It's pretty complex and pretty difficult for virus transmission to occur, which is a good thing," McAllister said.