DNREC Mosquito Control Section’s spraying season begins with larviciding wooded wetlands

Date Posted: Wednesday, March 22nd, 2017
Categories:  Division of Fish and Wildlife DNREC

DOVER – Weather-permitting, DNREC’s Mosquito Control Section within the Division of Fish & Wildlife will begin its annual spring woodland pool spraying campaign Thursday, March 23 downstate and possibly Friday, March 24 upstate, treating wooded wetlands near select populated areas in New Castle, Kent and Sussex counties. In most years, about 10,000 forested acres that produce large numbers of early season mosquitoes are strategically sprayed, using larvicides applied by helicopter and fixed-wing aircraft.

“The amount of spraying needed is determined by where and how wet the woodlands are, and can vary from year to year, depending on location and amount of precipitation that has occurred over the past autumn, winter and early spring,” said Delaware Mosquito Control Administrator Dr. William Meredith of DNREC’s Division of Fish & Wildlife. “Up until the recent nor’easter, our woodlands were much drier than normal for this time of year, but with recent rainfall standing water is now at about 70 percent of normal levels. This means we might treat 7,000-8,000 acres statewide during the upcoming weeks, instead of our usual average of about 10,000 acres.”

Over the next few weeks, Mosquito Control will apply a bacterially-produced insecticide, Bti. “Like all insecticides used by Delaware Mosquito Control, the U.S. Environmental Protection Agency has determined that Bti, when used in accordance with EPA-approved instructions as required by federal law, can be applied without posing unreasonable risk to human health, wildlife or the environment,” Dr. Meredith said.

Aerial spraying of woodland pools must be completed before the forest canopy fills in, usually around mid-April, because foliage prevents the insecticide from reaching woodland pools and other wet spots on the forest floor containing mosquito larvae. The spring campaign marks the beginning of Delaware’s annual mosquito season, which in most years continues until mid-October or early November, depending upon when the first killing frost occurs.

“If larval stages of early season mosquitoes are not successfully controlled, an intolerable number of biting adult mosquitoes could take wing in late April and remain through late June, becoming particularly troublesome within one to two miles of their woodland pool origins, and significantly affecting quality of life and human health for residents and visitors alike,” said Dr. Meredith.

“Delaware has about 100,000 acres of wet woodlands during most springs, and it’s not possible for logistical or budgetary reasons to larvicide all woodland mosquito-producing habitats,” Dr. Meredith continued. “Targeting wet woodlands near populated areas is the best return on investment in providing mosquito relief to the most people.”

With Zika virus in the news recently, Dr. Meredith said Mosquito Control’s initial annual spray campaign is not as focused on disease control as the section’s work will be later in the season. “The mosquito species in Delaware with the potential to transmit Zika is the Asian tiger mosquito, not the spring woodland pool mosquito,” he said, adding that Asian tiger mosquitoes typically appear later in the season.

“However, now is not too early for the public to take action to reduce backyard mosquito-producing habitat for species such as the Asian tiger mosquito that are known to carry illnesses such as West Nile virus and chikungunya as well as possibly Zika,” Dr. Meredith said.

Residents are strongly encouraged to reduce mosquito-producing habitat by cleaning clogged rain gutters and downspout extenders, keeping fresh water in birdbaths, draining abandoned swimming pools and preventing or emptying standing water from containers such as scrap tires, cans, buckets, flower pot liners, unused water cisterns, children’s toys, upright wheelbarrows, uncovered trash cans, depressions in tarps covering boats or other objects stored outside.

As in the past, public notice of when and where spraying for adult mosquitoes will occur this year will be available via daily radio announcements and by calling 800-338-8181 toll-free. Interested parties may also subscribe to receive email, text or phone message notices of mosquito control spraying in their area by signing up on the Spray Zone Notification System at

To request localized mosquito control, please call Mosquito Control’s field offices:

  • Glasgow Office, 302-836-2555, serving New Castle County and the northern half of Kent County, including Dover.
  • Milford Office, 302-422-1512, serving the southern half of Kent County south of Dover and all of Sussex County.

For more information about Delaware’s Mosquito Control program, please call the Dover office at 302-739-9917.

DNREC’s Mosquito Control Section provides statewide services to about 935,000 Delaware residents and 7.5 million visitors annually to maintain quality of life and protect public health by reducing the possibility of mosquito-borne illnesses such as West Nile virus, eastern equine encephalitis, chikungunya and Zika virus. Throughout the warmer months, Mosquito Control monitors and treats mosquito populations that emerge from wetland areas found throughout the state, including ditches, stormwater ponds, wet woodlands and coastal salt marshes. The Section also works year-round on water and marsh management projects designed to reduce mosquito populations, and provides the public with information on dealing with mosquitoes, from reducing backyard mosquito production to avoiding mosquito bites.

Media contact: Joanna Wilson, DNREC Public Affairs, 302-739-9902.

Vol. 47, No. 68


DNREC Logo The Delaware Department of Natural Resources and Environmental Control (DNREC). Want your news hot off the press? Join the DNREC press release email list. Send a blank email to
For more information, contact the DNREC Public Affairs Office, at 302.739.9902

The Division of Fish & Wildlife conserves and manages the fish and wildlife resources of the state, including restoration of habitats, and provides safe fishing, boating and hunting opportunities. Follow the Division on FaceBook.

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