Outline of
Madison's Mosquito Control Program
The
Madison Health Department oversees a Mosquito Control
Program that consists of a number of distinct but
complementary components. The primary goal of this
program is to control the population of mosquitoes in
order to reduce the public health threat of
mosquito-borne diseases and the nuisance associated with
large numbers of biting mosquitoes annoying residents.
Recently, there has been a great deal of media and public
attention given to Eastern Equine Encephalitis (EEE) and
West Nile Virus (WNV), two important mosquito-borne
diseases. The Town's Mosquito Control Program is based on
an integrated pest management (IPM) approach.
The first
component of this program is surveillance. The Town
coordinates with the State DEP and State Health
Department in the reporting of dead bird sightings in
Town. West Nile Virus seems to affect birds, particularly
crows, and the reporting of dead birds to the State
Health Department is an important surveillance tool in
tracking the spread of this disease. Dead birds that meet
certain criteria established by the State DEP may be
submitted to the DEP for virus isolation. The Connecticut
Agricultural Experiment Station collects mosquitoes from
a trap site in Madison and analyzes these mosquito pools
for the presence of WNV and EEE. The Town's mosquito
control contractor regularly inspects known mosquito
breeding areas in salt-marshes and publicly-owned
properties throughout town. These inspections consist of
collecting a sample of standing water and counting the
number of mosquito larvae and pupae present. The Madison
Health Department logs complaints from residents of the
incidence of biting adults in areas throughout town and
passes this information on to the contractor. Finally,
the Health Department and/or contractor perform bite
counts in areas identified by resident complaints to
verify the relative number of adult mosquito populations.
All of these surveillance activities, combined, provide a
picture of the abundance of mosquito populations and
their life stages, as well as the identification of
disease-carrying mosqutoes and/or birds. This
surveillance system allows population reduction
activities that can be more accurately targeted for
maximum effect.
The
second component of the mosquito control program is
population reduction through larval control. The Town's
mosquito control contractor places a biological
insecticide (Bacillus thuringiensis israelensis; Bti)
into portions of the salt-marshes and Town-owned
properties in which larvae are present, based on the
inspections noted above. This Bti is placed weekly during
the warmest part of the summer, and bi-weekly in the
spring and fall. In addition to this, the contractor
places another biological insecticide (Bacillus
sphaericus) into catch basins in which there is a
likelihood of mosquito breeding. The catch basins are
treated several times per year, beginning in mid-June and
ending in mid-September. These insecticides attack only
mosquito larvae, and do no harm to other aquatic
organisms. Bti is a cousin of other varieties of Bt that
are commonly used in gardens to control cabbage loopers
and other caterpillar pests. Bacillis sphaericus is
targeted to the Culex species of mosquito, which are some
of the most competent vectors of WNV and thrive in dirty
waters with high organic contents, such as catch basins.
The
Town's mosquito control program does not directly address
the control of breeding on most private property. The
public plays a very important role in the control of
mosquitoes. It is imperative that the public survey their
own property and eliminate any sources of standing water
that could become breeding areas for mosquitoes. Any
water that stands for more than 5 days could allow
mosquito breeding. Mosquitoes that have been shown to
most commonly carry WNV and EEE do not fly more than few
hundred yards, and thus, individual actions in each yard
are important in controlling the potential spread of
these diseases.
If
mosquito populations aren't sufficiently controlled in
the larval stage, large numbers may develop into adults
in just a few days during the warmest weather. Swarms of
adult salt-marsh mosquitoes can fly up to 15 miles and/or
be blown by the prevailing winds and become a nuisance to
large areas of town. Salt-marsh mosquitoes bite
aggressively throughout the day. Most freshwater mosquito
species, on the other hand, do not fly more than a few
hundred yards and primarily bite at dawn or dusk.
Following this outline is information on personal
protective measures that can be used to avoid mosquito
bites. Resident complaints and Town or contractor bite
counts are used to determine if a nuisance level of
adult-biting salt-marsh mosquitoes are present in an
area. If EEE or WNV is detected in a pool of mosquitoes
or a bird in town, the Town Health Department and First
Selectman, in consultation with the State DEP and
Department of Public Health (DPH) may recommend
ground-level spraying to control adult mosquito
populations in targeted areas.
A mild
insecticide may be sprayed into the air of the affected
area. The insecticide that is used is a synthetic
pyrethroid and is applied with a truck-mounted Ultra-Low
Volume mist sprayer. This technique ensures the maximum
coverage of the area with minimal insecticide.
Pyrethroids are synthetic versions of natural
insecticides derived from chrysanthemum flowers and
exhibit very low toxicity to mammals. These insecticides
break down in sunlight in 4 hours and leave no residue.
The disadvantage of this adulticiding is that it only
eliminates those mosquitoes that are hit with the spray;
there is no residual control. It is far more efficient
and cost-effective to control the mosquito populations in
the marsh, in their larval stage. This is why the Town's
control program concentrates heavily on larviciding.
