In the mosquito-control business, the primary measure of how things are going is called the “landing rate count.’’
It might also be called the slap test, because it entails standing in a spot for one minute and counting bites, like this: One. Slap! Two. Slap! And so on.
Judging by slap rates over the last month, South Florida could be facing another mean mosquito season. An early, wet start to the rainy season has triggered an unusually early explosion of buzzing hordes — and calls for help from bugged residents.
“This year it’s been extensive, intensive spraying since May,’’ said Chalmers Vasquez, mosquito control operations manager for Miami-Dade County. “I don’t even remember the last year we started spraying in May.’’
Drier weather over the last few weeks has helped, but when the heavy rains come again mosquito control agencies across South Florida are concerned about rising public health risks from illnesses spread by some species, including Dengue fever, West Nile virus and malaria. No cases have been reported in South Florida this year — but the mosquito season doesn’t typically peak until sometime in July.
Counties combat mosquitoes with chemicals that carry their own risks, particularly to the environment. The insecticides sprayed from trucks and planes — common brand names include Bi-Mist 30+30 and Dibrom — typically contain “broad spectrum” pesticides such as naled or permethrin.
They can irritate the eyes or skin of people exposed to low concentrations in fogging treatments, but they’re potentially toxic to marine and aquatic life. Studies have show they can have ripple effects across the marine food web, killing fish and conch larvae, but also affect desirable insects such as endangered butterflies that live in coastal hammocks.
Those residual impacts make controlling mosquitoes in South Florida extremely challenging. The island chain of the Florida Keys is surrounded by mangrove islands, fragile coral reefs and seagrass beds in federally protected waters. Miami-Dade is bordered by Everglades National Park and Biscayne National, both of which ban aerial and truck spraying, as do many state parks.
“It’s a balance that we need to walk of environmental protection and protecting people from mosquitoes,’’ said Michael Doyle, director of the Florida Keys Mosquito Control District.
Because of the restrictions on chemical spraying near water, for instance, the Keys’ control program employs a lot of larvicide — bacteria that selectively target the developing offspring of the region’s most common blood-sucker, the black salt marsh mosquito.
Mosquito control operations take steps to limit human exposure as well, scheduling spraying in pre-dawn or night hours that maximize the impact on bugs and minimize it to people.
While salt marsh mosquitoes are largely an annoyance, other species can be more dangerous, passing on a host of illnesses, including dengue, a nasty, flu-like illness that sickens some 50 million people annually. In severe cases, it can be fatal and there is no known treatment.
Dengue, carried by a mosquito called √Aedes aegypti, reemerged in Key West in 2009 with 27 cases, the first recorded in the continental United States since 1945. Another 66 cases were confirmed last year. Since 2010, Miami-Dade, Broward and Palm Beach counties also have reported a handful of cases.