(Reuters) - In Mississippi, a small team of entomologists has begun the first survey of mosquito populations in decades. Experts do not believe the kind of mosquitoes most likely to carry the Zika virus are active in the state, but they cannot know for sure.

By contrast, the Florida Keys Mosquito Control District, has been active since the late 1920s. With an annual budget of over $15 million, it now deploys four helicopters, two airplanes and 33 inspectors covering 125 square miles.

Because they are funded by local taxpayer dollars, U.S. mosquito control programs reflect deep economic disparities between communities, leaving some at-risk locations badly unprepared for the virus that is spreading through the Americas.

First detected in Brazil last year, Zika has been linked in that country to more than 1,300 cases of microcephaly, a rare birth defect defined by unusually small heads.

The outbreak is expected to reach the continental United States in the coming weeks as temperatures rise and mosquito populations multiply. In interviews with Reuters, more than a dozen state and local health officials and disease control experts say they worry they will have neither the money nor the time to plug gaping holes in the nation’s defenses.

They say the poorest communities along the Gulf of Mexico with a history of dengue outbreaks are at the highest risk.

States in the south are “woefully under-invested,” said Dr. Thomas Dobbs, epidemiologist for the Mississippi State Department of Health. “You have these gaping holes in capacity,” he said, with many poor communities mobilizing their first mosquito control efforts in years.

Among the best-prepared is Harris County, Texas, which includes the city of Houston. It dedicates $4.5 million a year to controlling disease carriers, or vectors, such as mosquitoes, ticks or rodents.

The 50-year-old program is considered one of the best in the country. Traps have been set up in 268 areas in the county to capture and catalog mosquitoes and test them for pesticide resistance. It is adding new traps for the Aedes aegypti mosquitoes that carry Zika.

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New York City plans to spend $21 million over three years to combat the virus. Aedes aegypti have never been found in the city, so its efforts will target Aedes albopictus, a mosquito believed to be capable of spreading the virus.

At the other end of the spectrum, some communities may only have a “Chuck in the truck” - someone who does spraying runs with a fogger attached to his pickup, said Stan Cope, president of the American Mosquito Control Association. Many municipalities do not even have that much.

The Obama administration has asked Congress for nearly $1.9 billion to fight Zika, including $453 million to assist with emergency response, laboratory capacity and mosquito control. Lawmakers in the House of Representatives and Senate have presented their own funding proposals, which each fall far short of that sum.

STOPGAP FUNDING

To help plug some of the gaps until Congress acts, the U.S. Centers for Disease Control and Prevention is adding $38 million to an existing infectious diseases grant program to expand lab testing capacity and surveillance for Zika.

For the first time, CDC will also provide an additional $15 million to help local programs most in need, CDC entomologist Janet McAllister told Reuters.

She said states’ proposals are due by the end of May and could cover funding for trucks, equipment and chemicals, as well as hiring contractors.

The CDC has also earmarked $25 million for at-risk states and territories, though the funds would primarily go health departments to help them deal with Zika cases.

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But the CDC money is not expected to reach states until August at the earliest, late in the game to do mosquito surveillance.

The agency estimates that Aedes aegypti could be present in as many as 27 U.S. states, though the chief worry will be areas with recent dengue fever cases, McAllister said. Those include South Florida, South Texas, Southern California, areas along the U.S. border with Mexico, Louisiana and Hawaii. (Graphic: tmsnrt.rs/1QvaMW6)

Frank Welch, medical director for the office of community preparedness for Louisiana, a state with 64 different types of mosquitoes, said his concern was that federal emergency funding might get delayed until the fall.

“That would certainly be too late for immediate Zika preparedness,” he said.

DIFFERENT ANIMAL

Even communities with established, well-funded insect-fighting programs may lack the tools to prevent an outbreak.

“We don’t feel horribly confident that anybody in the world is very good at controlling these mosquitoes,” said Susanne Kluh, Scientific-Technical Services Director for the Greater Los Angeles County Vector Control District.

One reason is that most U.S. programs are designed to deal with nuisance mosquitoes or those carrying West Nile, which are controlled by spraying at night and dropping tablets that kill mosquito larvae into catch basins.

Confronting Aedes aegypti, a daytime biter that lives in and around homes and breeds in tiny containers of water, is more expensive and inherently less efficient.

“It’s a different animal. It requires a very different method to control,” said Michael Doyle, a former CDC entomologist who directs mosquito control in the Florida Keys.

In 2009, Doyle oversaw efforts to fight dengue, also carried by Aedes aegypti. Inspectors went door to door every week, dumping containers of water in back yards that could serve as breeding sites, spraying pesticides to kill adult mosquitoes and using a liquid non-toxic bacterial formulation to kill larvae. After every rainstorm, they continue to spray 80,000 acres with the larvicide.

That has proved expensive at $16 per acre (0.4 hectare) plus helicopter costs. The efforts have only reduced the Aedes aegypti mosquito population by half since 2010, which Doyle said is not enough to prevent disease transmission.

In California, Aedes aegypti mosquitoes arrived as recently as 2013 and have spread to seven counties from south of Fresno to San Diego. “It has really changed the manpower needs,” Kluh said.

Kluh said her district traditionally treats easily accessible public areas, such as catch basins, storm drains and the occasional swimming pool.

“This battle against these mosquitoes happens in every backyard and in tiny sources as small as a bottle cap filled with sprinkler water.”