Picture a sky darkened by mosquitoes, an infestation so vicious that animals lumber toward lakes to seek relief. Baseball games are cancelled, and gardening requires head-to-toe gear.
Sounds like a thing of the past? Not necessarily. “We are keeping the wolf at the door,” said William Meredith, program administrator of the Mosquito Control Section of the Delaware Division of Fish and Wildlife, part of the Department of Natural Resources and Environmental Control. “If we weren’t working behind the scenes, we’d be one season away from experiencing those conditions again.
There are multiple reasons to stay on top of the mosquito population. Public health is a primary concern. Certain species carry West Nile virus and Eastern Equine Encephalitis (EEE), which affect both humans and horses. (The viruses can’t be transmitted from horses to humans.) In July, a crow tested positive for West Nile.
Peak activity for both viruses is from August to mid-October, according to the DNREC.
Mosquitoes can also transmit parasites and viruses responsible for malaria, dengue fever and yellow fever.
Economically speaking, mosquitoes can take a big bite out of tourism, particularly at the beach. And, quite simply, they’re annoying. Even just a few of these unwanted guests could spoil an outdoor picnic or camping trip.
Delaware’s Mosquito Control Section manages everything from pushing paperwork to securing funding to monitoring and controlling the population. “We’re soup to nuts,” said Meredith, a biologist with a doctorate.
Yet many residents have no idea of the huge effort and vast amount of time necessary to control these pests. The work starts in earnest in mid-March and continues until the fall freeze.
A plague of large proportion
In Delaware, the story of man versus mosquito is an old one. In 1788, an article in Columbian Magazine detailed the “evil” that afflicted residents near present-day Lewes.
“He, therefore, who shall visit this spot, whether from business or curiosity, will soon be taught to contemplate the moment of his departure with peculiar satisfaction,” according to the piece.
The counties of Kent and Sussex were named for two of the most malaria-ridden counties in England, Meredith noted. There are stories of Delaware livestock being bled to death by clouds of 10,000 mosquitoes, and it’s said that John Dickinson’s wife avoided his plantation near Dover because there were too many mosquitoes.
Prevention methods included spilling kerosene into standing water and applying oils to the skin. Then a well-traveled friend told Mary Wilson Thompson about places in Central America that drained swamps, ponds and other wetlands to reduce the mosquito population.
Thompson, who had a vacation home in Rehoboth, led a crusade to create parallel-grid ditches to drain excess water. The project gave jobs to the Civilian Conservation Corps. (CCC), which in 1933 started digging these canals across 44,000 acres of Delaware marshland. The Mosquito Control Section was established to oversee the project, and it took over when the CCC’s mosquito-control camps were abolished in 1937. (Once part of the highway department, its current home in an environmental protection agency is a rarity; only a handful of states have the same structure.)
As a preventative approach, ditching had problems. About 80 percent of the ditches drained water from places where mosquitoes weren’t even breeding. Ditching also devastated wetlands, home to birds, fish and other animals.
In 1956, when saltwater mosquito landing rates reportedly topped 50 per minute, concerned mothers organized a march on Dover to get the government to take action. Jack Smyth, publisher of the Delaware State News, ran with the story. “They talked about third world conditions in most of the lower portion of Delaware,” Meredith said.
As a result, using chemicals became more prominent. Pilot Allen Chorman recalls spraying for mosquitoes in 1967 for Joseph R. Hudson Aerial Spraying in Milford. “Mosquito Control would call down to Joe’s house and tell us where we were going,” he recalled. Although he missed the DDT era, the chemicals were harsh. “I wanted to fly so bad back in the day, I didn’t think about it,” said Chorman, who flew in an open cockpit.
Keeping an eye on ‘skeeters’
Instead of taking a routine, knee-jerk reaction to mosquito control, the section today heavily monitors the population before calling for aerial applications.
Surprisingly, the inspectors for the most part rely on tried-and-true devices. They use a white dipper, for instance, to take water samples to monitor larvae. “It’s pretty crude, but it works great,” said K.C. Conaway, program manager of the section’s Southern Kent County & Sussex County office in Milford. (There’s also a Newark office.)
To monitor adults, inspectors turn to New Jersey light traps. Developed in the 1940s, the trap has a light bulb to attract the bugs, and a fan to suck them through a funnel into a container with a pesticide strip. There are more than 30 traps located throughout the state.
Technicians identify the contents and enter data into a computer program. “They give us a good historic record about what type of mosquito is out there, and they let us know how treatments are working,” Meredith said.
To date, there are 57 different species in Delaware, including the aggressive Asian tiger mosquito that needs only a small amount of water to breed and leaves itchy, long-lasting welts. The section is currently awaiting positive identification on a possible 58th species that normally occupies warmer climes.
Other primitive but effective surveillance methods include standing in a mosquito-friendly area and counting how many mosquitoes land on you in a given time period. Sometimes, there are so many mosquitoes landing at once that inspectors hop right back in their car.
The section also encourages complaints from the public. “It helps us determine where to work,” Meredith said. “We put a lot of stock in public complaints.”
An ounce of prevention
Back in the 1960s, spraying covered a wide area and targeted adults. Today, the section also goes after immature mosquitoes using larvicides.
Jeff Corman, pilot for Allen Chorman & Son, offers an overview of mosquito spraying./h3>
Jeff Corman, pilot for Allen Chorman & Son, offers an overview of mosquito spraying.
Jeff Chorman, who uses a helicopter to hit small areas, particularly in the built-up beach area—may spend up to 14 hours a day in the air. But the areas are targeted. “We only spray larvicides when the larvae are there,” Meredith said.
Adulticides target flying or resting adults. Chorman might use a fixed-wing airplane or helicopter to deliver the application, depending on the area. The insecticides and the approach have been so effective that Allen Chorman & Son has seen a reduction in the mosquito-spraying side of their business in the past 50 years, Jeff Chorman said.
Still, mosquitoes are resilient, and the population varies from year to year and from month to month. During wet times, the section might call for an aircraft every day. The demand might taper off in dry months. Even so, warm weather and longer days speed the larvae’s growth cycle.
Mosquitoes that can breed in even a small amount of water—such as the depression in a tarp—can be problematic no matter the weather. Lately, swimming pools in foreclosed properties have become happy homes for mosquitoes, Meredith said. Staff may apply the insecticides to small areas using backpack sprayers or hand-tossed products. Trucks, meanwhile, address ditches alongside the road.
Natural control methods include stocking water bodies with larvae-eating fish. “They eat them like candy,” Conaway said. “They just love them.” Creating channels from ponds to isolated water-filled depressions allow the fish to travel to their food source.
Together, the natural methods and the insecticides are doing a good job, Meredith said. Indeed, most Delawareans think swatting the occasional mosquito or reaching for bug spray every now and then is ordinary. In fact, it’s anything but.
“They think this is natural, but this is very unnatural,” Meredith said of the controlled population. “And we work hard to make it seem that way.”