Florida Mosquito Populations Are Booming, but Diseases Aren’t

  • By:
    Stu Hutson – (352) 273-3569
  • Sources:
    Jonathan Day – jfda@ufl.edu, (561) 778-7200 x132
    Roxanne Rutledge Connelly – crr@ufl.edu, (772) 778-7200 x172

Alan Curtis uses his legs as bait in order to gauge the number of biting mosquitoes present after Hurricane David in 1979
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GAINESVILLE, Fla. — Sometimes, the tiny vampires cover Alan Curtis’ legs in writhing black. Other times, only a few come for a nibble.

Most days of the year – usually during the halcyon colors of twilight – Curtis, a mosquito expert with the Indian River Mosquito Control District, treads out into the marshes in his shorts and stands scarecrow for what’s called a “landing count.”

In other words, how many mosquitoes show up for dinner (i.e., his legs) in a span of 60 seconds.

“It’s probably about the best way to get an estimate of how many biting mosquitoes are out there at the moment,” Curtis said. “And it’s easy to see that it’s a good year for the mosquitoes.”

But it hasn’t been a good year for mosquito-borne pathogens.

Despite great concern earlier this year that conditions were ripe for outbreaks of mosquito-borne diseases such as West Nile virus and eastern equine encephalitis, researchers at the University of Florida’s Institute of Food and Agricultural Sciences say that the largest mosquito population in the last four years doesn’t seem to be commonly carrying diseases that are a threat to humans.

The lucky turn came in the form of an unusually intense and well-timed dry spell earlier this year, said Jonathan Day, professor of medical entomology at the university’s Florida Medical Entomology Laboratory (FMEL) in Vero Beach.

Mosquitoes aren’t the lone culprits in the life cycle of pathogens like West Nile virus. Their short life spans and flight ranges relegate them to the position of the local delivery men of disease. Much like the postal service needs airplanes, mosquitoes must pass their pathogen packages on to birds for the diseases to be widely spread.

The peak time for bird blood sucking is during nesting season, when the birds are uncommonly stationary and easy targets – usually from April to June. However, this year, the dry weather during that time meant there was no water in which mosquito eggs could hatch, and so few birds were infected.

Florida has had relatively wet weather since that time. And with none of the major storms or droughts that have disrupted mosquito populations over the last four years, reports from across the state show that their numbers are booming again, said Roxanne Rutledge Connelly, associate professor of medical entomology at the FMEL.

Exact numbers are difficult to gather because there are a variety of methods to evaluate the level of mosquito activity. While some counties use traps that lure mosquitoes in with carbon dioxide, other counties only count the number of requests they get for mosquito control. Then, of course, there are those like Curtis, who offer their own bodies as tools of measurement.

One thing all the methods agree upon, though, is that the number of mosquitoes is “off-scale” – more than can be accurately measured.

“Don’t let the fact that a major outbreak is nearly impossible fool you into not taking precautions,” Connelly said. With such large numbers of mosquitoes, disease will continue to be a threat until biting season ends in November.

For example, there have been 72 cases of eastern equine encephalitis in horses this year, all of which occurred in horses that most likely weren’t properly vaccinated against the disease. Florida residents should continue to control local mosquito populations by getting rid of standing water and protect themselves by wearing repellent.

“It’s like the chances of getting struck by lightning,” Day said. “Getting West Nile or something like it from a mosquito bite is unlikely. But just like you shouldn’t play golf in a thunderstorm, it’s best to be smart about how you deal with mosquitoes.”

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