It was well after midnight on a hot and sticky weeknight in Washington Heights in Upper Manhattan when the hunt got underway.
A police car rolled slowly through the empty neighborhood in the predawn hours, its lights casting shadows on the buildings as a voice over a loudspeaker blared a warning to clear the streets.
Following behind, at six miles per hour, was a white pickup truck carrying men in protective clothing and equipped with a machine intended to cast off a cloud of poison targeting the prey: mosquitoes.
The droplets would awaken any insects in the area, cause them to take flight and then kill them.
The spraying is called adulticide — as opposed to larvicide, or killing insects before they hatch — and it was the first time that such a truck had ever rolled through the neighborhood.
They were taking aim at Aedes albopictus, also known as the Asian tiger mosquito, a relative of the dreaded Aedes aegypti, the main transmitter of the Zika virus around the world.
While the Asian tiger mosquito has not yet been shown to be an effective vehicle for the spread of Zika, and there have been no locally transmitted cases in New York City, officials are still moving aggressively against the pest.
“We are just trying to kill Aedes mosquitoes,” Mary T. Bassett, the city’s health commissioner, said in a speech on Friday at New York Law School. “We are trying to push down a potential vector without evidence that it is yet a public health threat.”
At the current rate, Zika is on course to infect more than 90 million people around the world in the first wave of the epidemic, according to a study published last month in the journal Nature. That includes about two million women of childbearing age, and it could result in tens of thousands of babies born with devastating birth defects.
The already dire forecast could become even worse if sexual transmission, so far a proven means of contracting the virus, becomes more common and widespread or if the Asian tiger mosquito emerges as a competent carrier. Even the smallest genetic mutation in Zika could alter the ability for the virus to be spread by that mosquito.
While it is unclear what course the disease will take, officials say the battle against Zika must be broadly fought to keep the virus at bay. After all, as the country is witnessing in the greater Miami area, a cluster of locally transmitted Zika cases is difficult to stop once it is established.
Daniel Kass, New York City’s deputy commissioner for environmental health, said the city was better positioned than most other places to deal with the threat.
Still, the albopictus is in many ways a much more wily and industrious insect than the Culex mosquito, which carries West Nile virus and has been the focus of the city’s control efforts for the past 15 years.
“It is very labor intensive,” Mr. Kass said. “Not just for the city but for the public as well.”
The aegypti and albopictus mosquitoes share some traits that make them difficult to kill.
They can breed in a space as small as a bottle cap with a dollop of water. They lay their eggs just above the water line, so simply emptying a vessel with standing water will not kill them. Eggs can survive for months, waiting for the necessary rain to hatch.
And they are prodigious breeders.
Joseph M. Conlon, a retired Navy entomologist who is a technical adviser to the American Mosquito Control Association, gave an example of how fast their population can grow.
At the start of the mosquito season, even if there were just a single male and female Aedes in Manhattan in April, and 75 percent of their offspring were killed, that would still leave 800 million by October. If only 30 percent of their offspring died, there would be 50 billion.
Albopictus mosquitoes were not even found in North America until the 1980s, when they hitched a ride from Southeast Asia inside used tires shipped to Texas.
They are now found in about 30 states and are able to thrive in much cooler climates than aegypti mosquitoes, which has been in the country far longer, having arrived in the United States probably during the early days of the slave trade.
While both insects like to feed during the day, there are differences between them. Most critically, the aegypti feeds only on humans and prefers multiple meals of blood, making it a highly efficient virus spreader.
The albopictus, on the other hand, feeds on both humans and animals, which in turn lessens the odds that it will be as effective in passing the virus.
But they are both hard to kill, and New York City is investing heavily in its campaign. Of the $21 million that officials have dedicated to combat Zika over the next three years, $11.2 million is being used to improve mosquito control.
The number of trucks used for spraying is increasing to 27 from seven, and the city has doubled the amount of spraying it does both on the ground and from the air.
The health department has also trained and licensed about 60 people from other city agencies to exterminate mosquitoes and has expanded the use of backpacks to spray in small, confined locations.
New York has deviated from the Centers for Disease Control and Prevention’s guidance on mosquito control, which has been used in places like Miami. There, each case of Zika contracted overseas has been tracked and then an aggressive control effort is made near the home of the infected person.
But in New York, a city of over eight million people with nearly 500 imported cases of Zika — about one-quarter of the national total — health officials have preferred to use enhanced surveillance, demographics and information about known travel patterns of residents to target certain parts of the city as opposed to tracking individuals.
To aid in the effort, the number of mosquito traps across the city have also been doubled, with 60 focused on the albopictus. The sites are surveyed weekly and more traps are added to locations with high mosquito populations.
This week the city is starting a website — www.nyc.gov/health/mosquito — so the public can track mosquito spraying and other surveillance information.
In addition to killing the pests, the city is also looking for any mosquito that could be carrying the Zika virus. The health department has five mosquito trappers and five taxonomists who sort through the catch every day.
One of the taxonomists is Feven Asefaha, who estimates that on a busy day she sorts through 1,000 mosquitoes, casting off the males and putting the females in a vial, where they will be crushed and then tested for Zika.
“Time goes fast when you are sorting through mosquitoes,” said Ms. Asefaha, as she sat in front of a microscope and a petri dish holding the latest batch of insects.
In another room in the lab, the mosquitoes are run through machines that look like printers but are actually sophisticated testing equipment. They cost $75,000 each; the city has bought two more and has three on order to keep up with the growing demand.
Jennifer Rakeman, the assistant commissioner for the Public Health Laboratory, said the department could handle the workload. “But if we had a measles outbreak or some other emergency, we would max out,” she said.
The city is also starting a more robust campaign to make the public aware of its role in the effort against the virus.
Still, officials acknowledged the challenges they face.
“It is going to be problematic to get rid of those mosquitoes,” Mr. Conlon said.
When Mr. Conlon testified before Congress in April, he made it clear that traditional control efforts would not be enough.
“We need a national initiative where we make it simply socially unacceptable to have conditions in a backyard that allows mosquitoes to grow, like the antismoking campaign or anti-littering campaign,” he said.
The stakes are high.
If the aegypti remains the primary transmitter, mosquito-spread viruses will be largely confined to Latin America, the Caribbean and the Gulf States.
Should the albopictus become an effective transmitter, however, most of the United States, parts of Canada, much of western Europe as well as South and East Asia would all be at greater risk.
The Pan-American Health Organization recently reported that tests on albopictus mosquitoes in Mexico came back positive for Zika.
But perhaps most worrisome is the role the mosquito has played in spreading other similar viruses, especially chikungunya, which causes fever and muscle pain.
Dr. Bassett, the city’s health commissioner, said in her speech on Friday she was optimistic that there would be no local outbreaks of Zika, though she added that the city was prepared if one occurred.
Still, she said, in a globalized world where new and exotic microbes are only a plane ride away, the city could not let down its guard. “Get ready,” Dr. Bassett said. “We are going to have more of these kind of outbreaks in the future.”