Weather permitting, DNREC’s Mosquito Control Section will start its annual spring woodland-pool spraying on Wednesday, March 25, treating wooded wetlands near populated areas in New Castle, Kent and Sussex counties. Several thousand acres where early season woodland pool mosquitoes breed in quantity will be treated by helicopter and possibly fixed wing aircraft, with the focus on areas near cities, towns and large developments.


Weather permitting, DNREC’s Mosquito Control Section will start its annual spring woodland-pool spraying on Wednesday, March 25, treating wooded wetlands near populated areas in New Castle, Kent and Sussex counties. Several thousand acres where early season woodland pool mosquitoes breed in quantity will be treated by helicopter and possibly fixed wing aircraft, with the focus on areas near cities, towns and large developments.

Control efforts will target the immature (larval) stages of early-season woodland pool mosquitoes. Aerial spraying of woodland pools must be completed before the forest canopy fills in with leaves, usually around mid-April, because leaves will prevent the insecticide from reaching pools and other wet spots containing larvae on the forest floor.

If larval stages of these early season mosquitoes are not successfully controlled, an intolerable number of biting adult mosquitoes could take wing by early to mid-May and remain through late June, becoming particularly troublesome within one to two miles of their woodland pool origins, and significantly affecting local quality of life for residents and visitors alike. 

According to Mosquito Control Program Administrator Dr. William Meredith, with about 100,000 acres of wet woodlands in Delaware, it is not possible for budgetary, logistical and environmental reasons to larvicide all woodland mosquito-rearing habitats. “For best return-on-investment in providing mosquito relief to the most people, only woodland pools near populated areas will be treated,” said Meredith. “During these tight budget times, it’s more important than ever that we deliver our needed control services as cost effectively as possible.”

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

The amount of spraying needed is determined by where the woodlands are and how wet they are, which can vary from year to year depending on the location and amount of precipitation that has occurred over the past autumn, winter and early spring. “Woodland pool wetness in downstate areas is pretty normal this year, although upstate areas have been a bit drier,” Meredith said, noting that could change over the next few weeks if we get a lot of rain. “The relatively mild temperatures this past winter probably won’t have much bearing on this year’s mosquito production,” he added.

The annual spring woodland-pool treatment program in late March and early April marks the beginning of Delaware’s mosquito season, which in most years continues until around late October and can last as long as mid-November, depending upon when the first killing freeze occurs. On a year-round basis, the Mosquito Control Section also performs non-insecticidal work, involving water and marsh management projects designed to reduce mosquito production. These projects often have marsh habitat restoration or enhancement components that benefit fish and wildlife populations.

While some species of spring mosquitoes may carry West Nile virus, the mosquito species primarily responsible for transmitting this disease to humans or horses - mainly the common house mosquito and close relatives - arrives later in the year from sources other than woodland pools. The other mosquito-borne disease of concern to humans and horses in Delaware, eastern equine encephalitis, is primarily transmitted by the common saltmarsh mosquito during late summer and early fall, as well as by a few species of freshwater mosquitoes from mid-summer into autumn.

“Delaware is in the top 10 states in the country for percent wetlands cover, making us a naturally ‘buggy’ state.  We’re also in the top 10 states for human population density, with both factors then combining for an unholy mix of mosquito-induced complications and challenges,” Meredith said.

The public is encouraged to do its part to reduce mosquito-rearing habitat by cleaning clogged rain gutters, keeping fresh water in birdbaths, draining abandoned swimming pools and emptying standing water from such containers as scrap tires, cans, flower pot liners, unused water cisterns, upright wheelbarrows, uncovered trash cans, depressions in tarps covering boats or other objects stored outside.  

For more information on Delaware’s Mosquito Control program, call 739-9917 in Dover. To request local relief, call Mosquito Control’s field offices at 836-2555 (in Glasgow) for New Castle and northwestern Kent counties, or 422-1512 (in Milford) for most of Kent and all of Sussex counties.

Advance public notice of when and where spraying will occur is given daily via radio announcements, on a toll-free hotline at 800-338-8181, or on DNREC’s website, www.fw.delaware.gov/services/MosquitoSection.htm.

Interested parties may also subscribe to receive e-mail notices by visiting the DNREC homepage -- click on “Email List Subscription” under Services and follow directions to sign up for mosquito control spray announcements.