Mosquitoes
All mosquitoes found within the District's boundaries belong
to one of two groups: Floodwater
mosquitoes or permanent and stagnant water mosquitoes. Membership in one or the other group is
dependent on the type of environment in which the female mosquito chooses to
lay her eggs.
FLOODWATER MOSQUITOES, such as Aedes vexans, lay
their eggs on dry ground in areas that are subject to flooding following
sufficient rainfall. These eggs lay
dormant until sufficient inundation occurs to initiate hatching. Hatching is synchronized, and development
from egg to a blood-feeding adult can occur within 7 to 10 days. Areas within the District serving as
production sources for such mosquitoes include swamp and marsh margins, roadside
ditches, poorly maintained detention ponds and the floodplains of the Des
Plaines River and associated creek systems.
Floodwater mosquito species are the most bothersome and prolific
mosquitoes affecting District residents.
STAGNANT WATER MOSQUITOES lay their eggs directly on the
water surface, either singly or in a cluster or raft. The production sources are constantly replenished with the next
generation's eggs, resulting in constant emergence of new adults. Human biting species occurring within the
District include Coquillettidia perturbans, Anopheles punctipennis,
and Anopheles quadrimaculatus.
More importantly, however, are species in the Culex pipiens
complex, which are known to be competent vectors of Saint Louis Encephalitis,
West Nile Virus and are believed to be responsible for both amplification of
the virus in birds and transmission to man.
This District therefore places a high priority on the suppression of the
members of this medically important group.
The
Terrain
The topography of the District is quite diversified. Although much of the area was originally
swampland and floodplain, early settlers in the area installed field tiles and
open ditches to drain much of the land for agricultural use. Unfortunately, heavy urbanization in recent
years has caused the destruction of many of these drainage systems, and has
resulted in the reintroduction of flooding problems solved long ago. This has resulted in the creation of a large
number of both floodwater and stagnant water mosquito sources in close
proximity to heavily populated areas.
In addition, undeveloped outlying areas in, and adjacent to, the
District contain extensive acreage of floodwater mosquito production
sites. Urbanization also creates its
own mosquito problems with the construction of catch basins, detention/retention
ponds, culverts and man-made water holding containers like tires, flower pots,
un-maintained swimming pools, clogged rain gutters, stagnant bird baths, etc.
Control
Methods
The operations of the District are designed to conform to
the concepts set forth in the theory of integrated pest management. Primary emphasis is placed on the elimination
of target populations when they are in their most vulnerable and concentrated
stage of development. In the case of
mosquitoes this is, of course, the aquatic larval stage. Principle focus is placed upon annual
surveys of the District to locate and map both permanent and temporary mosquito
production sources, and to routinely inspect these areas, treating only those
sources found to produce mosquitoes.
Additional efforts are made to eliminate sources through water
management projects whenever possible.
Finally, temporary relief is provided through adult control measures in
those areas in which surveillance traps indicate a need. Public education about
mosquitoes and their control is also an integral part of our management
approach. The District continually
evaluates ongoing control practices in effort to provide the latest integrated
pest management approaches and methods least likely to affect human/wildlife
health or the environment.
Field
Operations
Mapping
An effective mapping system to aid field personnel in
locating mosquito production sources is crucial to any mosquito abatement
operation. The mapping system used by
the NWMAD is an extension of the township mapping system. The 242 square miles of the District are
contained within all or part of 9 contiguous townships; each of these is, in turn, divided into 36
one square mile units called sections.
By applying a catalogue number to each potential source within a
specific section in a given township, we can quickly refer to and locate a
given source within the District. Over
5,500 potential mosquito production sources have been found and catalogued to
date.
Once the potential source has been located and numbered,
color-coding of the map is implemented to further distinguish the type of
mosquito
source. In this fashion, red denotes
water sites (or portions thereof) which are considered temporary, green is used
to indicate semi-permanent or permanent water sites which potentially can
produce mosquitoes and blue is reserved for those water holding areas which
have not shown any mosquito production for at least four years. Color-coded maps, then, allow the District
to quickly adjust its focus to a particular type of mosquito production source
as field conditions change.
Aquatic Larval Control
Once an accurate mapping system has been established, a
routine inspection and treatment program can be implemented to control
mosquitoes while they are concentrated, relatively immobile, and accessible in
the larval stage. The NWMAD larviciding
program is the principle thrust of its overall operation, accounting for
approximately 90% of "in season" manpower effort. An attempt is made to inspect each potential
source at approximately 7-10 day intervals throughout the mosquito production
season. Only those sources found to
harbor mosquito larvae are treated.
Using the catalogue numbers created during the mapping process,
inspection and treatment records for each source are compiled in a computer
data base, which is then used to monitor the frequency of visits and mosquito
production at a given source. Those
sources found to be dry during the drought conditions are temporarily removed
from the inspection lists, allowing man-hours to be directed to those sources
most likely to produce mosquitoes. All
sources temporarily removed from the inspection list are reinstated after
sufficient rainfall to cause inundation has occurred.
Three types of larvicide's are used in the District's control
efforts. A monomolecular film (MMF) is applied to the surface of the water using motorized backpack
sprayers, truck-mounted power sprayers, and all-terrain-vehicles. MMF's will kill all mosquito developmental stages at
the water surface. Microbial insecticides Bacillus thurengiensis israelensis (Bti) &
Bacillus sphaericus formulated granules
are applied to inundated areas covered with dense vegetation. The granules effectively penetrate the
ground cover, and the Bti then kills the larvae. Application of these microbial insecticides at the labeled rates
pose little health concern to humans, wildlife and the environment according to the
EPA. Finally, methoprene (Altosid), a
mosquito/midge/blackfly specific insect growth regulator, formulated into briquettes/pellets
is applied to catch basins and floodwater areas. This material prevents the mosquito pupae from making the
transformation to adulthood. It has the added benefit of allowing mosquito
larvae development, thus, providing for the food chain and nourishing natural
mosquito larva predators and parasites.
Source Reduction
Eliminating the aquatic larval habitats of the mosquito is the most effective and efficient method of controlling mosquitoes. Due to current wetland restrictions the majority of of the Districts source reduction efforts are now focused on construction/ development consultation and homeowner source reduction methods. In addition, the District works with Forest Preserve Districts and environmental groups interested in constructing wetlands less conducive to mosquito production.
Adult Control
Although corrective water management projects and the
routine inspection and treatment of mosquito production sources are
unquestionably the principle focus of the District's efforts, provisions in the
overall program must be made to reduce adult populations when they reach an
unacceptable level from either a nuisance or public health standpoint. Nuisance mosquito populations, for example,
can sometimes increase drastically due to invasion from the extensive untreated
wetlands which border the District on three sides. Additionally, dispersal behavior characteristic of floodwater
mosquitoes can be extensive making adult mosquito control more difficult. An
alert from the Illinois Department of Public Health of a potential outbreak of
St. Louis encephalitis or West Nile Virus would constitute grounds for adult
control aimed at species of the Culex pipiens complex. In any case, adulticiding operations are
viewed to be a temporary, but necessary, solution to a pressing problem.
The decision to prepare for and initiate adulticiding
operations is based on the disease surveillance, projected emergence date, the projected density of
that population, and the prevailing weather conditions at the time of
emergence. Adult population levels are
monitored daily through the use of New Jersey light traps and gravid traps. Finally, adulticiding is carried out only
when prevailing wind speed and temperatures are within acceptable limits. Treatment is carried out a few hours between
sunset and midnight or a few hours just before sunrise, when the mosquitoes
exhibit the most activity.
The District's adulticiding program uses Ultra Low Volume
(ULV) spray machines mounted on truck beds to disperse a non-thermal aerosol of
the synthetic pyrethroids; Anvil (sumithrin) or Scourge (resmethrin). The average particle size (mass median
diameter) sprayed is around 15 microns, and is dispersed creating a 300 foot
swath width. All spray units are serviced
and recalibrated on a routine basis.
Droplet diameter and rate of application conform to regulations and
label recommendations in accordance with the Federal and State EPA, the
Illinois Department of Public Health and the Illinois Department of
Agriculture.
Entomology
Department
The District laboratory provides the information on current mosquito population levels and weather conditions necessary to make timely and prudent tactical decisions in both the larval and adult control programs. In addition, it provides for the education of field employees, as well as the general public. The specific responsibilities of the laboratory staff are as follows:
Placement of New Jersey light traps, gravid traps and other traps to monitor the migration and movements of adult mosquitoes into and within the District.
Daily collecting, sorting, and
identification of all adult mosquitoes obtained from the light traps during the
mosquito production season.
Daily sorting and identification of all
larval mosquitoes collected by field operators.
Testing mosquitoes for St. Louis
encephalitis, West Nile Virus and other arboviruses with in-house detection methods or outside arboviral laboratories.
Monitoring of rain gauges and computerized
weather stations to provide information necessary to predict flights of
floodwater mosquitoes.
Testing and calibration of all ULV spray
units used to abate adult mosquitoes as required by State law.
Education of employees to prepare them for
tests required to obtain the Illinois Department of Agriculture Applicator/Operator Pesticide
licenses.
Presentation of educational programs to
interested public groups, such as grade schools, junior and senior high
schools, library and public service organizations.
Responding to public telephone inquiries
concerning District operations.
Assisting residents with their particular
non-mosquito insect problems, as time permits.
Collection of data for research projects.
The Entomology Department may be contacted at: entomologydept @ nwmadil.com
Internal Services
The Department of Internal Services is responsible for the
upkeep of equipment utilized by the District, necessary for the implementation
of control procedures. A fleet of 50+ trucks, modified with District control
equipment, are regularly serviced and maintained year-round. In addition, 2 All-Terrain-Vehicles (ATV)
for larviciding in large sources often inaccessible to crews on foot, 1 backhoe
and 1 dump truck are maintained.
Internal Services also regularly maintains power backpacks,
pump-packs, and granular spreaders used throughout the season by field workers
in the suppression of mosquito populations.
Inventory, security, and safe storage of insecticides also lies within
the Department's jurisdiction.
Personnel
Structure
The District maintains a staff of 12 full-time employees and hires approximately 52 seasonal workers during the mosquito production season. All employees involved in field operations are licensed by the Illinois Department of Agriculture for mosquito control work. This organizational structure keeps personnel costs down while providing the experienced supervision needed to efficiently carry out the objectives of the District.