HomeMy WebLinkAboutSWP272000(10) (2) 1/7�
CITY OF RENTON
PANTHER CREEK WETLANDS MOSQUITO ABATEMENT PROGRAM
MOSQUITO CONTROL ALTERNATIVES REPORT
_DECEMBER 11 , 1991
Prepared for
The City of Renton
Y1 .3nni.na/Buiidinci/Public Works Department
Prepared by
Terry Whitworth , PhD . Entomologist
Whitworth Pest Control , Inc .
TABLE OF CONTENTS
Forge
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Problem Statement . . . . 4
Review or Mosquito Control Tactics in other Areas . . . . . . . . . . . 7
Comparison or Mosquito Control Options . . . . . . . . . . . . . . . . . . . . . 11
Biological Control Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Chemical Control Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Biorationalchemicals 17
Syntheti4Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Citizen Mosquito Control Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
DOE Mosquito Control Policy. . . . . . . . . . . . . . . . . . . 20
Conclusions and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
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INTRODUCTION
This report is to satisfy a condition of a determination of
non-significance issued by the hearing examiner on February 27 ,
1989 . The city was required to explore mosquito control options
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for the Panther Creek Wetlands with a review of positive and
negative impacts before rhP and_-o 1_
L>fx P6SSJbL .voSQjk6 LonAJ�
�-$ The city has made a variety of mosquito abatement efforts in and
around the Panther Creek Wetlands since the mid- 1970 ' s - The author
has been involved in these efforts since 1979 . Control efforts
were begun in response to complaints from homeowners in the Talbot
Hill area above the wetlands . Early measures which involved
misting wetland borders with pesticides , did little to abate the
problem_ In the early 1980 ' s the dominant species of mosquitoes
were identified and several aerial applications of residual
synthetic pesticides were made . These treatments appeared to be
effective, but environmental concerns eliminated this approach
by the mid- 1980 ' s . Since then, the city has directed its efforts
toward solving the mosquito problem, while also addressing citizen
and governmental concerns about protecting the fragile wetland
environment.
Historically mosquito-borne diseases have caused more human illness
and death than all other diseases combined. As a result,
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mosquitoes have probably been studied more than any other insect.
Hosquito control principles have been long-established and
remained virtually unchanged for the past 40 years .
The most effective , and long lasting form of mosquito control is
the elimination of mosquito breeding habitat, by filling , dredging ,
channelizinq or water level manipulation _ Other options include
biological , and chemical control .
The value of preserving large rural wetlands as sites for waterfowl
breeding and feeding has been recognized for decades , but small
urban wetlands like the Panther Creek site , until recently, were
considered to be of little value . However, as urban wetlands have
been eliminated , with expanded construction of parking lots ,
driveways, and buildings , flooding problems have increased . This
has lead to an increased awareness of the value of urban wetlands
and growing political and regulatory requirements to protect them.
THE PROBLEM
In 1991 the author conducted a detailed study of the mosquito
problem in the Panther Creek Wetlands )( see attached report ) .
There are three common genera of mosquitoes which occur i.n the
Panther Creek Marsh , Coquillettidia, Culex, and Aedes .
4
T
Coquillettidia includes only a single species , ( C . preturbans )
while Culex, and Aedes include several species each . Also found
occasionally in the area were Culiseta sp. and Anopheles sp.
Coquillettidia preturbans have been the most serious pest in
the marsh . It thrives in this environment because its larvae
attach to rooted aquatic vegetation such as cattails , one of
the dominant plants in the marsh . This species has only a
single generation per year unlike most mosquitoes . Eggs may
-hatch as early as, March and adults usually begin emerqinq in
early May. Adult emergence can occur over a 2-3 month period ,
though most adults will have emerged by mid-July.
Incidentally, this species occurred in much lower numbers and
much later (July ) in 1991 than in past years .
Culex, species have free-floating larvae which thrive in
stagnant pools throughout the swamp . They emerge later than
Coquillettidia and are not nearly as pesky to humans , though
they can carry disease. Members of this genus have multiple
generations , but at the Panther Creek site , they tend to
appear, from mid-summer until late September. Species of this
genus favor warm, stagnant or polluted water.
Aedes species are known as floodwater mosquitoes and also have
free-floating larvae . They are serious pests where
5
fluctuating water levels occur. Species of this genus were
responsible for the majority of complaints received in
1991 . The best defense against this pest is to have a water
management plan which prevents frequent water level
fluctuations _ This species has multiple generations and under
the right conditions ( warm weather after rain or high water )
produce new generations in as little as one week . This genus
was rarely collected in past years , but it occurred in large
numbers in 1991 from April to September. Aedes does not come
to light traps as well as the other two groups and many were
hand-collected during our monitoring effort. Perhaps they
were abundant in previous years, but not collected because we
relied almost exclusively on light traps for our samples in
the past .
The mosquito problem in the Panther Creek wetlands has resulted in
a classical dilemma which is also occurring throughout the nation
wherever wetlands and human populations are in close proximity.
Governmental regulations , backed by citizen support , require
wetland preservation , but those same citizens have little tolerance
for mosquitoes . Wetland protection efforts have limited many
proven mosquito abatement tactics, such as filling , dredging , or
draining wetlands . Until recently, conventional synthetic
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pesticides such as Dursban 2G provided economical , effective
mosquito control . In the past few years "environmentalist"
opposition to these pesticides has grown and resulted in regulatory
changes which greatly limit aquatic insecticides that can be used
at the Panther Creek site . The result is the only pesticides
allowed at this site are the "biochemical" materials which include
Altosid and Bacillus thuringiensis israelensis ( Bti ) . These
products can be effective when used properly, but they are much
more expensive . A cost comparison example which includes only
material cost is mosquito treatment with Dursban 2G costs about_
S5 . 00/acre while Altosid XR costs S550.00/acre .
The Panther Creek site has up to 65 acres of wetlands rsee attae4t -
wetlands inventory, -june__ L9-9-1 ) so the total chemical cost for
Dursban 2G would be $300 . 00 , while the cost of Altosid XR would be
$33 , 000 . 00 . a hundred fold difference . Bti is much less expensive ,
but is very short- lived ( about 24 hours ) and must be reapplied
regularly to be effective . It also will not control
Coguillettidia, which lives underwater attached to the roots and
stems of plants ( most larvae float at the surface ) .
A REVIEW OF MOSQUITO CONTROL TACTICS IN OTHER AREAS
In an effort to develop an overview of mosquito control options , I
interviewed a number of mosquito control experts statewide and
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nationwide . Names were obtained from the membership rolls of the
American Mosquito Control Association .
Most experts on mosquito control manage mosquito abatement
districts in areas where mosquitoes pose a human disease threat _
These managers are invariably publicly funded , with limited
budgets , and usually use proven control techniques . Until
recently, proven techniques meant, where possible and economically
feasible , to fill , dredge , or drain mosquito breeding sites _ In
areas where this was not feasible , long lasting synthetic
larvacides and adulticides were used. They were relatively
inexpensive , and effective . However, environmental concerns grew
about the effect of these pesticides on non-target organisms , and
the public has demanded safer alternatives . Unfortunately, " safer"
has often meant more expensive and less effective .
Districts on the East Coast and California are ahead of those in
the Northwest , because they were pressured to change their tactics
many years ago . This pressure has developed only recently in the
Northwest. The following is a summary of mosquito control programs
I investigated throughout the United States.
Within Washington Jim Thompson , head of the Grant County Mosquito
Abatement district and Executive Director of the Northwest Mosquito
Control Association is probably one of the most innovative mosquito
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manaqers in the state . Other active managers I interviewed were
Dick Morton ( Benton County ) , and Al Huber (Yakima County ) . Each of
these individuals are responsible for mosquito problems in eastern
Washington , where disease transmission is a major concern . They
have recently begun moving away from hard chemicals and are
increasing the use of products like Altosid and Bacillus
thuringiensis . However synthetic larvacides and fogging of adults
is still a major part of their programs . Limited funds have kept
them from researching much new technology.
In Portland , Oregon , Peter DeChant is in charge of the Multnomah
County Mosquito Abatement Program. As in Washington , the program
has minimal funds and creative research opportunities are very
limited.
In California Dr. Bruce Eldridge is director of mosquito research
at University of California, at Davis . He is an acknowledged
mosquito expert and is pursuing a variety of creative mosquito
control approaches . I discussed the Panther Creek Wetland problem
with him in detail , but he could add little to what we already
know. He provided me with names of several other experts including
Dr. William Hazelltine , Manager of Butte County, California,
Mosquito Abatement District, Cy Lesser Maryland Department of
Agriculture , and Judy Hansen , Cape May, New Jersey. I called each
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of these persons and found that, though they have different
mosquito problems , they are also dealing with the same small pool
of solutions. Their districts also suffer from underfunding which
makes it difficult to research new mosquito control options .
In California and on the East Coast the use of Gambusia ( top-feeder
minnows ) to control mosquito larvae is one of the most effective
alternatives to pesticides . The use of biological control agents
will be discussed in more detail later.
In the process of preparing This document . I reviewed manv
articles and texts . One of the best is titled , "Guidelines for the
Ecological Control of Mosquitoes in Non-Tidal Wetlands of the San
Francisco Bay Area" . Research for this document was supported by
the California Mosquito and Vector Control Association and the
University of California Mosquito Research Program.
Ecological control is defined as "the exploitation of ecological
relationships to reduce population size or production rate of a
disease vector or pest organism" . This method leads to reduced
average and peak mosquito densities and is useful where
environmental concerns require a reduction in the use of
pesticides . It is also useful to consider ecological factors when
restructuring wetlands to ensure you don ' t create new mosquito
habitat. In general , this control method alone , is not acceptable
le
to citizens who want to preserve wetlands while havinq no
mosquitoes .
It appears that , if ecological controls are to be used in the
Panther Creek Wetlands site , some major changes must be made . To
determine what changes would be most likely to provide the desired
results , many hydrological factors must be taken into account ( see
Hydrological Factors , Appendix #1 ) . 130 I�WJ5
L�" fir,s',.J, b T 7
Wetlands typically experie e extreme changes in quantity and
quality of water supplies . A major rainstorm may introduce
sediments , oils , and other pollutants to the wetland . An extended
s�Sdrought may cause it to go dry. Detailed studies by the city are
kyj--*109Y 4'\A 'nv�k-o,.d 1,c s /
underway to determine the sees of w- r_xr _�* the Panther Creek
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site, r ui o popu ations.
COMPARISON OF MOSQUITO CONTROL OPTIONS
The following is a review of the cities choices with the Panther
Creek Wetlands , as I see it :
Option 1 . Suspend city mosquito control efforts and let
homeowners handle the problem individually.
Pros - Saves the city money.
- Does not disturb the wetland .
Cons - May anger residents above wetlands .
- May lead to homeowner remedies which are
hazardous to the environment .
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Since state law ( see RCW 17 . 28 . 170 ) mandates that property owners
must control mosquitoes on their property, the city may be
obligated to control mosquitoes originating on their propertv.
Option 2 . Continue treating water with Altosid Briquets and
fogging upland areas with Scourge , make no habitat
changes .
Pros - Does not require large up-front dollars .
- Wetland is preserved.
Cons - Mosquito control success will vary depending_
on water levels . etc .
- Pesticide usage will remain the same or
higher depending on water levels .
- Would cause continuing concerns about impact
of treatments on environmental quality.
This approach is probably the best choice until effective ,
acceptable alternatives have been clearly identified .
Option 3 . Make habitat changes to improve mosquito control
efforts such as access paths through vegetation or
small ponds. Improve paths along edge .
Pros - Relatively inexpensive .
- Would allow more consistently effective
mosquito control.
- Would not change the present wetland .
Cons - Channels would have to be kept open.
- The program relies primarily on the use
of pesticides.
This approach is similar to option 1 and should be considered , if
the final decision is no major habitat modification will be done .
Option 4 . Provide wetland outflows with gates to allow
manipulation of water levels in the wetland .
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Pros - Would be relatively inexpensive .
- Would not require extensive chanq_es in the
wetlands .
- Would provide a method of environmental
control of mosquitoes .
Cons - Altering water levels will have a negative
impact on some marsh inhabiting plants and
animals .
- Without channels , it is not clear how well
the wetlands would drain if gates were
opened .
Option 5 . Channelize the wetlands to prevent standing water.
Pros - Would reduce mosquito breeding sites .
- Would reduce size of areas that need to be
treated , and reduce pesticide use .
Cons - Could reduce size of wetlands .
- Would require periodic maintenance to prevent
channels from filling .
- Could cause downstream flooding_ .
- Would be relatively expensive .
This proposal and the ones that follow may invoke the "no net loss
Cal
of wetlands" policy of the/ and Federal government . These
changes would certainly change the nature of the wetlands , but
whether it would cause a net loss would have to be determined by
regulatory officials .
Option 6 . Build a series of ponds connected by channels with
water levels controlled by flood control gates .
Pros - Wetlands nature is retained.
- Open water would encourage fish, ducks .
geese . and other wildlife , while reducing
mosquitoes .
- Mosquito predators such as Gambusia may
survive and breed in this situation .
- Would reduce size of mosquito breeding sites
and amount of pesticides needed .
- Water levels could be manipulated to control
mosquitoes .
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- Could make the area attractive to the public
for fishing; bird watching ; etc .
Cons - Ponds would have to be dredged periodically
to keep silt out.
- Application of aquatic herbicides may be
needed to control floating weeds and rooted
vegetation.
- Could be expensive to develop and maintain .
Option 7 . Construct a large lake with a flood pate .
Pros - Would reduce mosquito breeding sites .
- Could open the area up for public recreation .
- Would allow water level manipulation which
would help control mosquitoes .
Cons - Would be expensive to construct .
- Would eliminate wetlands, as such .
- Would require aquatic weed control .
- Could contribute to downstream flooding .
Option 8 . Utilize a combination of these options.
Construction of a series of ponds or a lake , creates open water
which reduces survival of larval mosquitoes because of wind and
wave action . To minimize mosquito and weed production these water
bodies need steep sides , and around 1 foot drop for every 3 feet
from shore . The water needs to be as deep as possible , at least 6
feet deep at low water levels to minimize rooted aquatic vegetation
and maximize fish survival . This option comes with its own share
of problems . Ponds or lakes will tend to fill with silt from
runoff if they are not dredged periodically. If they are allowed
14
to fill , another swamp will be created . Open water can also
develop problems with Eurasian milfoil and algae . These problems
can be treated with aquatic herbicides, but there many associated
expenses and environmental concerns .
Equipping the outlet with a gate will allow manipulation of water
levels and provide a means of controlling mosquito larvae by
desiccation . Fluctuating water levels have been used successfully
in California and on the East Coast to control many species of
mosquitoes . Once eggs have hatched , many larvae will die when
water levels drop suddenly. This approach risks aggravating Aedes
problems if previously dry areas are re-wet for a week or more .
Another solution would be to construct a series of ditches which
would keep the wetlands free of standing water. When water
accumulates after rains , it would be drain out rapidly and provide
little mosquito breeding habitat. However , this would also change
the nature of the wetlands. For some ideas on how to modify
mosquito breeding habitat see New Jersey' s recommendations ,
Appendix 2 , on "Best Management Practices for Mosquito Control " .
BIOLOGICAL CONTROL ALTERNATIVES
The Panther Creek Wetlands contain a variety of vertebrates which
can reduce mosquito populations ( see 1991 Wildlife Survey ) . The
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wetland is populated with three-spined sticklebacks , and several
species of frogs which will feed on mosquitoes . It also has
several species of swallows which feed almost exclusively on tlyinq
insects . Though bats were not inventoried in the wetlands . it is
likely that some inhabit the area and they teed nocturnally on
flying insects like mosquitoes .
Studies have shown that three-spined sticklebacks feed extensively
on mosquito larvae and pupae . However they rarely occur in
Sufficient numbers to cause a major reduction in mosquito
populations (Chapman , 1985 ) . Since these fish are already present
in the Panther Creek wetlands , its apparent that they alone cannot
keep breeding mosquitoes under control .
There are a variety of insectivorous birds inhabiting the wetlands .
Birds such as tree swallows could be encouraged by the installation
of nest boxes along the wetland borders . It is generally believed
that, while animals like birds and bats can reduce mosquito
populations, they cannot control them.
The use of stocked Gambusia sp ( mosquito fish ) to reduce mosquito
populations has been well-documented (Chapman , 1985 ) . Under ideal
circumstances, this minnow can substantially reduce populations of
mosquito larvae and pupae . It is a hardy and adaptable fish which
can be quite prolific . It cannot be considered a panacea for
16
mosquito problems and there are many records of control failures
with Gambusia . It is best used as part of an integrated pest
management ( IpM ) program. This fish has been implicated in the
elimination of rare and endangered minnows ( through habitat
destruction ) and will eat eggs of desirable fish species . Any
decision to stock Gambusia would require prior permission from the
Washinqton State Department'(of Wildlife . a-�O
CHEMICAL CONTROL ALTERNATIVES
Chemical applications to water for mosquito control are -regulated
by the Department of Ecology ( see attached DOE mosquito control
policy, September 1991 ) . Normally only Bacillus thuringensis
israelensis ( Bti ) and methoprene liquid (Altosid ) are allowed for
use on mosquitoes by Department of Ecology in the state of
Washington . To justify the use of "stronger" chemicals it must be
shown that Bti or Altosid would be ineffective or fail to abate a
public health problem.
BIORATIONAL CHEMICALS
1
Bacillus thuringensis israelensis ( Teknar and Bactimos ) is an
endospore forming bacterium which when ingested by early instar
larvae can kill them . It has the advantage of being relatively
host specific, but it must be reapplied frequently to be effective ,
` 17
and as a result is very expensive . It also does not control some
mosquitoes , such as Coquillettidia which attach to vegetation below
the water surface .
Methoprene ( Altosid ) is a growth regulator which prevents the
emergence of normal adult mosquitoes . It is available in liquid ,
pellet , and briquet form . The advantage of this product is that it
does not remove immature mosquitoes from the food chain and it
tends to have minimal impact on non-target organisms . It is also
available in a long lasting briquet form which reduces the
frequency of treatments needed . All biological chemicals tend to
be much more expensive than synthetic chemicals .
SYNTHETIC CHEMICALS
Larvacides
The DOE mosquito control policy ( as of September 1991 ) lists
acceptable synthetic mosquito control larvacides . The list is
in order of perceived hazard to the aquatic environment .
Monomolecular surface film ( Aerosurf MSF ) leads the list alonq
with Golden Bear Oil . Products such as temephos , fenthion ,
and chlorpyrifos are at the end of the list because they tend
to be broad spectrum and eliminate many non-target
invertebrates from the aquatic environment .
18
Adulticides
Mosquito adulticides are applied to upland areas only and
therefore are regulated by the Washington Department of
Agriculture . There are no special restrictions on adulticides
and therefore any product registered in Washington State and
labeled for outdoor misting of mosquitoes can be used . In
environmentally sensitive areas , products like Scourge ( SBE'
1382 ) , a synthetic pyrethroid , are preferred. This product is
short- lived ( about 4 hours ) and is sate around birds and
mammals . In heavy mosquito infestations it must be reapplied
frequently to achieve control . A newly registered product for
adult mosquito control is permethrin ( also a synthetic
pyrethroid ) which can last up to 7' days after application .
L1bv,
Products like Dursban ( chlorpyrifos ) are also long lasting and
effective but there is more concern about its effect on non-
target organisms .
CITIZEN 140SQUITO CONTROL OPTIONS
There are a variety of things homeowners can do to reduce mosquito
breeding on their property. Standing water anywhere outdoors will
provide mosquito breeding sites . Things like bird baths and wading
pools should be emptied weekly to keep larvae from reaching the
adult stage . Other possible breeding sites include old tires ,
19
plugged putters , and mud puddles. These tactics will reduce Culex
populations. but would not effect Aedes or Coquillettidia which
breed in wetlands .
Homeowners can also go indoors to avoid mosquitoes and equip doors
and windows with screens . When outdoors they can wear protective
clothing and mosquito repellent . Many people resent the tact that
they can ' t enjoy their property at certain times of year, without
protecting themselves . They tend to blame the citv for the
/y kt (1 �y oufi S 5o y,t o� T��r+�c�ty�cl/2c r1 t �s2u5Q d �s Po�u/ ii+e a w
mosquitoes, since mart
DEPARTMENT OF ECOLOGY MOSQUITO CONTROL POLICY
w�SQ� WS
In September 1991 . DOE issued a final draft of a mosquito control r
policy ( see attachment ) . This policy was developed by a committee
of state regulators ( DOE , Department of Health , and Department of
Agriculture ) and industry representatives, including the author . To
apply pesticides to water for mosquito control a short-term
modification permit must be obtained from DOE . To obtain this
permit the applicator must: 1 . Present a treatment plan , 2 .
Comply with the State Environment Policy Act ( SEPA ) checklist
requirements and 3 . Get a determination of nonsignificance ( DNS ) .
The DOE must be informed of the time period when treatments will
occur and have access to the results of any monitoring program
available . The public must be notified at least 24 hours in
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advance of any maior treatment. DOE regulates only pesticide
applications to water while the Department of Agriculture regulates
upland treatments . No state permit requirements exist for
applications to upland areas .
CONCLUSIONS AND RECOMMENDATIONS
The solution to this mosquito problem must be left to the citizens
and the political entities governing the Panther Creek Wetlands .
In my opinion , the approach which would provide the most reduction
in mosquito populations , while retaining the wetland character , is
the construction of a series of ponds with water control gates .
This would result in improved fish and waterfowl habitat and the
open water would greatly reduce mosquito breeding. However , this
approach would be expensive to develop and might be costly to
maintain .
Individuals or special interest groups who insist on preserving
wetlands need to recognize that preservation comes with a price
tag. A wetland so close to an urban area will be a continuing
source of citizen complaints about mosquitoes and require ongoing
city expenditures to keep them in check. If the site were to
become a public recreation area , perhaps better funding to maintain
the area would follow. In Washington State the Centennial Clean
Water Act , managed by the Department of Ecology, provides grants to
21
local communities to preserve and manage wetlands . The city may
want to consider pursuing assistance through this avenue to improve
the wetlands . Before initiating expensive changes in the Panther
Creek site , the city should recognize that mosquitoes are breeding
z-
throughout the Hiqhway 167 corridor and adults can fly up to 7
miles from where they breed. The brushy hillside between Talbot
Hill and the wetlands will continue to harbor some adult mosquitoes
from elsewhere , even if they are controlled in the wetlands .
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w
s
REFERENCES
Chapman, H. C . Editor. 1985 . Biological Control of Mosquitoes .
American Mosquito Control Association , Fresno , CA .
218 P .
Collins . J . N . & V. H . Resh. 1989. Guidelines for the Ecological
Control of Mosquitoes in Non-tidal Wetlands of the
San Francisco Bay area. California Mosquito and
Vector Control Association . 93 P .
Mulhern, T . D. 1980- A Training Manual for California Mosquito
Control Agencies . CMCA Press , Visalia, CA .
O ' CarroII , G. 1988 . Best Management Practices for Mosquito Control
& Freshwater Wetlands Management. New Jersey
Department of Environmental Pretection . 74 P .
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