3 - Nuisance Mosquito Control Pilot Program Report ~`~y °t Bou~er Nuisance Mosquito Control
Pilot Program Report
Prepared for:
City of Boulder
Office of Environmental Affairs
P.O. Box 791
Boulder, Colorado 80306
Prepared by:
OtterTail Environmental, Inc.
10200 W. 44`h Ave., Ste. 210
Wheat Ridge, CO 80033
Phone:303-858-8350
~O~t~r~ail
Environmental z
January 2009
I
TABLE OF CONTENTS
1.0 INTRODUCTION AND PILOT PROGRAM DEVELOPEMENT ...........................................................1
INTRODUCTION ..........................................................................................................................................................1
PILOT PROGRAM DEVELOPEMENT .............................................................................................................................1
2.0 METHODS ......................................................................................................................................................3
2.1 STANDARD WNV PROGRAM METHODS SUMMARY ......................................................................................3
2.1.1 Standard Mosquito Larvae Surveillance and Control Methods ................................................................3
2.1.2 Standard Adult Mosquito Surveillance Methods .....................................................................................3
2.2 PILOT PROGRAM METHODS ..........................................................................................................................4
2.2.1 Pilot Program Larval Site Selection Methods ..........................................................................................4
2.2.2 Pilot Program Larval Surveillance and Control Methods ........................................................................5
2.2.3 Pilot Program Adult Surveillance and Control Methods .........................................................................5
3.0 RESULTS ........................................................................................................................................................6
3.1 LARVAL SURVEILLANCE AND CONTROL RESULTS ........................................................................................6
3.1.1 Evaluation of Nuisance Mosquito Larval Control Threshold .................................................................8
3.1.2 Results of the Mosquito Working Group Collaboration ..........................................................................9
3.2 ADULT MOSQUITO SURVEILLANCE AND CONTROL RESULTS ........................................................................9
3.3 EVALUATION OF THE EFFECTS OF THE PILOT PROGRAM ON COMPLAINT NUMBERS ...................................14
3.4 EVALUATION OF THE EFFECT OF INCREASING THE SPRAY THRESHOLD ON ADULT SPRAYING FREQUENCY
............................................................................................................................16
3.5 EVALUATION OF TRAP BC- 43 TO ASSESS THE EFFECTS FROM NOT CONDUCTING NUISANCE LARVAL
CONTROL ON NEARBY SITES .......................................................................................................................17
3.6 EVALUATION OF POTENTIAL ENVIRONMENTAL IMPACTS OF PESTICIDE USE ..............................................19
3.6.1 Potential Long-Term Impacts ofBti Treatments on Biota .....................................................................19
3.6.2 Potential Effects of ULV Spraying on the Environment .......................................................................20
4.0 SUMMARY OF PILOT PROGRAM RESULTS ......................................................................................21
5.0 PILOT PROGRAM OPTIONS,. .............................................................,....,.......................,.......,......,.......22
FIGURES
Figure 1 Percentages of Site Treatments for Nuisance and Culex Larvae per Month, 2007 ..................................7
Figure 2 Percentages of Site Treatments for Nuisance and Culex Larvae per Month, 2008 ..................................7
Figure 3 Weekly Adult Trap Counts at Sombrero Marsh (Trap H2), 2006-2008 ................................................11
Figure 4 Weekly Adult Trap Counts at Sombrero Marsh (Trap BC-32), 2006-2008 ...........................................11
Figure 5 Weekly Adult Trap Counts at Gapter Rd/Old Tale (Trap BC-O1), 2006-2008 ......................................12
Figure 6 Weekly Adult Trap Counts at Stazio Ballfields (Trap C11), 2006-2008 ................................:..............12
Figure 7 Weekly Adult Trap Counts at Thorne Institute (Trap C12), 2007-2008 ................................................13
Figure 8 Weekly Adult Trap Counts at EBCC (Trap C 13), 2007-2008 ...............................................................13
Figure 9 Weekly Adult Trap Counts at San Lazaro MHP (Trap BC-43), County ULV Spray Events, and
Nuisance-Only Larval Occurrences at Sites Within One Mile of the Trap, 2007-2008 ........................19
TABLES
Table 1 Comparison of Larval Surveillance and Control During the Pilot Program vs. What Would Have Been
Performed With the Standard WNV Program .........................................................................................6
Table 2 Larval Treatment Summary by Month, 2007 and 2008 Combined ........................................................8
Table 3 Comparison of Larval Populations Controlled During the Pilot Program vs. What Would Have Been
Controlled with the Standard WNV Program ..........................................................................................8
Table 4 Number of Treatments for Nuisance-Only Species Mosquitoes by Property, 2007-2008 .......................8
Table 5 Comparison of Site Treatments, Site Locations Treated, and Estimated Nuisance Larval Population
Controlled with Differing Dip Count Thresholds, 2007-2008 .................................................................9
Table 6 Number of Adult Mosquitoes' per Trap for the 2007 Season .................................................................10
Table 7 Number of Adult Mosquitoes per Trap for the 2008 Season .................................................................10
Table 8 Average Number of Mosquitoes of the Pilot Program Area Traps, 2006-2008 .....................................14
City of Boulder Pilot Program Report ; OtterTail
Environmental
Table 9 Trap Counts for Greenbelt Meadows Neighborhood Temporary Trap, 2008 ........................................15
Table 10 Comparison of Larval Surveillance and Control Activities at 35 Habitat Sites Within One Mile of the
Greenbelt Meadows and Gapter Rd. Neighborhoods Had They Been Included in the Pilot Program vs.
What Was Performed With the Standard WNV Program, 2007-2008 ...................................................16
Table 11 Comparison of the Number of County ULV Spray Applications Using the Pilot Program's 250
Threshold vs. the Previous Pre-Pilot Threshold of 100 .........................................................................17
Table 12 Comparison of Larval Surveillance and Control Activities at 13 Habitat Sites Within One Mile of the
San Lazaro MHP Neighborhood Had They Been Included in the Pilot Program vs. What Was
Performed With the Standard WNV Program, 2007-2008 ....................................................................18
Table 13 Theoretical Larval Populations Based on Differing Dip Counts in 0.5 Acre Habitat ............................22
APPENDIX A:
Map A-1 Pilot Program Larval Sites
Map A-2 Pilot Program Adult Trap Locations
City of Boulder Pilot Program Report ~ i Atte~I'ail
Environmental
1.0 INTRODUCTION AND PILOT PROGRAIVI DEVELOPEIIAENT
INTRODUCTION
Since the spring of 2003, the city of Boulder has conducted a vector management program designed to
protect public health and biological resources from the effects of West Nile Virus (WNV). The design of the
West Nile Virus Mosquito Management Plan (WNV program) allows for mosquito control with the larvicide,
Bacillus thuringiensis israelensis (Bti) only for species of mosquitoes that are known to most effectively
transmit the disease to humans (Culex or vector species) and bypasses treating habitats that only contain
species of mosquito larvae that are a nuisance to people (nuisance or non-vector species). It also contains a
contingency plan for adult mosquito ultra low volume (ULV) spraying applications if WNV activity
escalates to a public health emergency. For more detailed background information about WNV and the
vector program in Boulder, please reference the 2006 City of Boulder West Nile Virus Mosquito
Management Plan prepared by OtterTail and the city of Boulder (www.environmentalaffairs.com).
While the results of the WNV program suggest that it has been highly effective at protecting the public
against the threat of WNV, there were certain issues that developed with the vector-only approach to
mosquito control. These issues were:
1) In May and June of 2006, mosquito breeding conditions were ideal, and the city of Boulder received
hundreds of complaints about nuisance mosquito activity from softball players and attendees at
Stazio Ballfields and golfers at Flatirons Golf Course. These Parks and Recreation (P&R) facilities
began realizing decreased revenues from declining attendance associated with these complaints.
2) The city received a large number of complaints in 2006 about high numbers of nuisance mosquitoes
from city and county residents living adjacent to several Open Space and Mountain Parks (OSMP)
properties.
3) The city was informally requested by the Board of County Commissioners and Boulder County
Public Health (BCPH) to begin performing larval control for nuisance mosquitoes. The county felt
that they were spraying pesticides for adult mosquitoes (adulticiding) more often than if the city
would conduct nuisance larval control on the city lands that are nearby county lands.
PILOT PROGRAM DEVELOPEMENT
After the 2006 mosquito season, the city conducted several meetings to develop a strategy to address these
issues. As a result, the Nuisance Mosquito Control Pilot Program (pilot program) was developed. The pilot
program was started in 2007 and was intended to be a two-year trial program to reduce the nuisance
mosquito populations within the areas of concern. During the development of the pilot program, the
following goals were determined to be needed:
1) Treat Larval Sites For Nuisance-Only Occurrences: The city would perform control treatments for
any type of mosquito larvae in breeding sites deemed to be potentially important producers of large
numbers of nuisance mosquitoes that were within influence of the areas of concern. These breeding
sites were predetermined during planning meetings before the initial field season began. The city did
this for two primary reasons: 1) to reduce the number of nuisance mosquito complaints; 2) as an
incentive to have the county make an effort to decrease adult spraying.
A) Reduce the Number of Nuisance Mosquito Complaints: The city wanted to reduce the number of
complaints originating from patrons of the city's revenue-generating facilities and selected
residential neighborhoods.
City of Boulder Pilot Program Report I .Otte mTai,l
B) Decrease County Adult Sprang: The city was concerned about the environmental effects of the
county's adulticiding on adjacent lands, so they were willing to compromise and treat the pilot
program.larval sites for all types of mosquitoes if the county would make an effort to decrease
adult spraying. This would increase the number of Bti applications on the city wetlands and their
biota, but would potentially benefit other biota by reducing adulticide applications, which is
considered to be more harmful than Bti.
In order to get nuisance larval control performed by the city, the county decided to compromise
and increased the adult mosquito threshold that triggered adulticiding from 100 mosquitoes per
trap a night to 250 in these problem areas where the city would do nuisance control.
2) Implement aNuisance-Only Larval Control Tri Bring Threshold: Many groups had segments of
their constituency that were divided on the issue of treating for nuisance mosquitoes. Some wanted
to maintain avector-only program to keep some of the wetlands from receiving additional Bti
applications, while others wanted all types of mosquitoes to be treated.
A compromise was reached to use a threshold for nuisance mosquito treatment. Although there
would still be a Bti treatment anytime Culex larvae were found breeding, the city implemented a dip
count threshold for nuisance larvae so that a site breeding low levels of nuisance species and no
Culex would not have pesticides applied to it.
3) Establish a Mosquito Workin Group: The city wanted to establish a "Mosquito Working Group"
involving staff from the city's Office of Environmental Affairs (OEA), OSMP, and P&R
departments, along with staff from BCPH and OtterTail to develop best management practices
(BMPs) for mosquito control per the city's Integrated Pest Management (IPM) process.
4) Evaluate the Potential Environmental Impacts of Pesticide Use: As part of this pilot program, the city
decided to address some of their ongoing concerns about the potential impacts of pesticides on the
environment. This included an evaluation of the potential effects of the county adulticide
applications on waterways and the city Bti applications on biological resources.
City of Boulder Pilot Program Report 2 ~tterTail
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2.0 METHODS
2.1 STANDARD WNV PROGRAM METHODS SUMMARY
The following section provides a brief overview of the city's standard WNV program methods. For a
detailed explanation of the larval surveillance methodology used for the WNV program, please see the 2006
City of Boulder West Nile Virus Mosquito Management Plan.
2.1.1 Standard Mosquito Larvae Surveillance and Control Methods
Larval mosquito surveillance and control methods employed by OtterTail were aimed at reducing the
potential of the mosquito-borne disease, West Nile Virus. The program's focus for larval control was to
identify if Culex species were present before initiating control efforts. To increase the effectiveness and
efficiency of larval control efforts, OtterTail identified two groups of mosquitoes: 1) Culex species (or
vector) category and 2) all other species into a nuisance only (or non-vector) category.
The threshold for larval control was presence of Culex species. The method allowed for nuisance
mosquitoes to persist in the environment if vector species were not present. This approach typically requires
more surveillance, but resulted in less treatment of wetlands and other nonvector mosquito breeding habitats.
Unlike an indiscriminate mosquito control program, where presence of any type of mosquito larvae triggers
treatment, the presence or absence of Culex species was determined before the site-specific larval treatment
could occur.
Finding and documenting consistent Culex breeding sites was an important component for the program
because, once identified, these sites could be routinely monitored and systematically controlled. One goal of
larval mosquito control is to prevent the need for adult mosquito control spraying, which is typically less
effective and more expensive than larval control. By differentiating between vector and non-vector larvae,
the larval mosquito program also provided an early WNV warning system. Because larvae obviously show
up before adults, if vector larvae are identified, it gives us approximately two weeks more notice than if only
adults are identified.
In balancing environmental effects, cost effectiveness, and public health needs, Bti was chosen as the
primary treatment method. Other larval control materials were available but were not used for the WNV
program. Bti is a larvicide that is a naturally occurring protein which is toxic to mosquito larvae upon its
ingestion. It provides a residual treatment that can last for approximately two days.
Since new mosquito larvae may hatch after the product dissipates, the sites need to be inspected for mosquito
larvae every 1 to 2 weeks, depending on the time of the season. The existence of mosquito larvae between
monitoring periods has the added benefit of allowing mosquito larvae to still be part of the aquatic food
chain, but will be eliminated before they can emerge as adults. This helps protect the public from WNV,
while still providing an important food source for many animals.
Bti was applied at the recommended rates, thereby minimizing any potential adverse impacts to areas being
treated. Routine post-treatment checks were conducted in 24 hours to assure the larval population was
controlled. If any Culex larvae were found, a second application of the control material was applied.
2.1.2 Standard Adult Mosquito Surveillance Methods
Adult mosquito population surveillance is a crucial component of any successful WNV and mosquito control
program. Adult surveillance can provide information on what types of mosquito species are in an area as
well as information on their abundance. Adult mosquito surveillance is also critical to disease surveillance.
Mosquitoes collected from the mosquito traps can be tested for a variety of mosquito-borne diseases,
including WNV.
City of Boulder Pilot Program Report 3 ~~Cl~d~l
OtterTail uses two different types of mosquito traps to monitor adult mosquito populations in the WNV
program, the gravid trap and the carbon dioxide (COz) light trap (light trap). The light traps are based on the
principle that most adult mosquitoes are attracted to light, COZ (via respiration), and heat. The light trap
collects a wide variety of adult female mosquitoes that are seeking a blood meal. The gravid trap mimics
sources of mosquito breeding habitat and attracts gravid female mosquitoes that are seeking a spot to lay
their eggs. Due to its mimicking of stagnant breeding habitats, which is the preferred breeding habitat of
Culex mosquitoes, gravid traps typically collect a much larger amount of Culex species than nuisance
species. Both types of traps were set overnight and on the following morning the nets were collected and
returned to the OtterTail lab where the mosquitoes were identified and counted. Once identified, the
mosquitoes were then sorted by species and the vector mosquitoes were submitted to the Colorado
Department of Public Health and Environment (CDPHE) for WNV testing.
Beginning in June, twelve light traps and four gravid traps were set so that each would cover an
approximately one-mile radius. Traps were set in areas of suitable harborage for adult mosquitoes within the
WNV program area. The city cooperated with the University of Colorado (CU) and BCPH in order to
provide complete surveillance coverage for the city. The 16 city traps, in combination with the BCPH and
CU traps, provided comprehensive surveillance of the Boulder urban area. All 16 traps were set on a weekly
basis until mid-September.
OtterTail used the adult mosquito data to calculate potential WNV infection rates and to help city officials
determine local areas of concern for public awareness and safety. This data could also be used to guide any
potential adulticide efforts within the city, which was an important health and environmental issue to city
officials and residents.
2.2 PILOT PROGRAM METHODS
2.2.1 Pilot Program Larval Site Se/ecfion Methods
In the winter of 2006-2007 the city of Boulder and OtterTail analyzed the four years of larval surveillance
data from the city's WNV program to identify which sites should be added to the pilot program project area
to most effectively reduce nuisance mosquito populations in the areas of concern (revenue generating areas,
high complaint residential areas and areas potentially influencing county spraying). The initial
recommendations included 137 sites from the WNV program that were within a one mile radius of the city
revenue generating areas and residential areas that were producing high numbers of complaints of nuisance
mosquitoes. After negotiations among several city departments (OEA, P&R, and OSMP) and city boards, 57
sites were approved to be added into the pilot program project area for nuisance mosquito larval control
(Map A-1). Although they were not areas believed to be a source of the mosquitoes affecting the high
complaint areas, P&R added several breeding sites located around Boulder Reservoir and Pleasantview
Soccer Fields during the site selection negotiations, to reduce the nuisance mosquito populations around
those areas. The final sites that were added to the pilot program are located on the following city-owned and
private properties:
Parks and Recreation Properties Open Space and Mountain Parks Properties
• Gerald Stazio Ballfields • Sombrero Marsh
• Flatirons Golf Course • Burke II
• Pleasantview Soccer Fields
• Boulder Reservoir Private Properties
• Valmont Park • Western Disposal property in or near city limits
• Christensen Park • Thomas Hogan and Charles Pancost properties
• East Boulder Community Center (EBCC) near EBCC
• Kentucky Property
City of Boulder Pilot Program Report 4 .~~te mTila
1
2.2.2 Pilot Program Larval Surveillance and Control Methods
OtterTail used the same methods as those in the WNV program, with the following four changes:
1) Recorded nuisance and Culex species separately on the larval surveillance field form and database.
Prior to the pilot program, OtterTail noted nuisance species only when Culex species were not
present. When Culex species were present, even if nuisance species were also present, the visit was
recorded as having only Culex species. This was because the nuisance species were also controlled
whenever Culex was present.
2) During each field visit, technicians differentiated between areas of a site that were not currently
breeding and those that were, to more accurately be able to estimate what each site's larval
production potential would be.
3) Began larval surveillance and control several weeks earlier than the standard WNV program to
control the nuisance species that typically emerge earlier than Culex species.
4) Implemented a dip count threshold (1 larva per dip) for nuisance species so sites with only low levels
of nuisance species and no Culex would not have Bti applied to it. (Presence of any Culex is the
standard for treatment in the standard WNV program.)
2.2.3 Pilot Program Adult Surveillance and Control Methods
The pilot program used the same methods previous to the program, with the following six changes:
1) Since gravid traps typically collect a much larger amount of Culex species than nuisance species,
they were not used in the pilot program's adult mosquito surveillance; light traps were used
exclusively.
2) For the pilot program, the city of Boulder and OtterTail chose two additional locations for adult
mosquito monitoring (see Map A-2). The two additional traps were used in combination with two of
the WNV program traps to monitor adult mosquito populations within the pilot program area and to
aid in the evaluation of the success of the pilot program's larval control efforts. Since the focus of
the additional surveillance was to monitor adult mosquito populations around the high complaint
areas of the pilot program, extra traps were not placed around the Boulder Reservoir or Pleasantview
Soccer Fields. The four locations and trap names used in the pilot program were:
Standard WNV Program Traps Additional Pilot Program Traps
- Sombrero Marsh (Trap H2) -Thorne Institute (Trap C12)
- Stazio Ballfields (Trap C11) -East Boulder Community Center (Trap C13)
3) OtterTail used trap data provided by BCPH to help with the evaluation of the pilot program. As part
of their standard mosquito control program, BCPH set traps on a weekly basis throughout the county
during the pilot program. Three of the BCPH traps were set in locations near the pilot program and
BCPH provided the city of Boulder and OtterTail the trap data from those locations. The three traps
that they provided data for were:
BCPH Program Traps
- Old Tale/Gapter Road (Trap BC-01)
- Sombrero Marsh Trap (BC-32)
- San Lazaro (Trap BC-43)
City of Boulder Pilot Program Report ~ -~tte mTa it
4) OtterTail began adult surveillance several weeks earlier than the standard WNV program to control
the nuisance species that typically emerge before Culex species.
5) OtterTail did not submit Culex mosquitoes from the additional pilot program traps to CDPHE for
WNV testing, as WNV monitoring was not the purpose of these new traps.
6) BCPH raised their adult trap threshold associated with their 3 traps listed above, that would trigger
adulticiding from 100 to 250.
3.0 RESULTS
3.1 LARVAL SURVEILLANCE AND CONTROL RESULTS
As shown in Table 1, over the course of the two-year study, a total of 1,878 individual larval site visits were
performed on the 57 potential breeding sites. Approximately 75 acres of active breeding habitat were
identified and treated at 32 sites. There were a total of 54 site treatments performed for Culex-only species,
88 site treatments performed when both Culex and nuisance species were present and 33 site treatments for
nuisance-only species over the course of two seasons. Therefore the pilot program increased the number of
site treatments by 33 (or 19%), which increased the amount of acreage treated by 11 acres (30%) and the
amount of Bti applied by 57 pounds (30%).
Table 1 Comparison of Larval Surveillance and Control During the Pilot Program vs. What Would
Have Been Performed With the Standard WNV Pro ram
Increase Due to
Year Pilot Program Standard WNV pilot Program;
(Nuisance)1 Program (Culex)Z
Number Percent
2007
Potential Breeding Site Locations 57 57 0 0.0%
Number of Site Investigations 832 721 111 13.3%
Number of Site Treatments 54 41 13 24.1%
Number of Site Locations Treated 17 16 1 5.9%
Total Treated Acreage 42.2 34.9 7.3 17.3%
Pounds of Bti Used4 211 174.5 36.5 17.3%
2008
Potential Breeding Site Locations 57 57 0 0.0%
Number of Site Investigations 1,046 865 181 17.3%
Number of Site Treatments 121 101 20 16.5%
Number of Site Locations Treated 22 19 3 13.6%
Total Treated Acreage 33.4 17.8 15.6 46.7%
Pounds of Bti Used' 167 89 78 46.7%
2-Year Avera e
Potential Breeding Site Locations 57.0 57.0 0.0 0.0%
Number of Site Investigations 939.0 793.0 146.0 15.5%
Number of Site Treatments 87.5 71.0 16.5 18.9%
Number of Site Locations Treated 19.5 17.5 2,0 10.3%
Total Treated Acreage 37.8 26.4 11.5 30.3%
Pounds of Bti Used" 189.0 131.8 57.3 30.3%
Notes:
1: The implemented program for those two years
2: Results if the Standard WNV program had been done instead of the Pilot Program
3: Difference between Pilot Program and what would have occurred had the Standard WNV Program been implemented instead
4: Amount of B[i used when applied at the typical 5 lbs. per acre application rate
City of Boulder Pilot Program Report ~ ~OtterTail
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The number of site locations receiving Bti treatments and the amount of Bti being used for mosquito control
was a concern of several city staff members and residents. Although the amount of Bti that was used
increased by 30%, the results of the pilot program show that the additional site treatments for nuisance
mosquitoes increased the number of site locations treated by only 4 locations (or 10%) over the course of the
program. The increase in site investigations (15.5% increase) and treatments (approximate 19% increase)
due to the pilot program also increased the overall labor and material costs associated with those activities.
To help understand patterns of larval species presence and treatments throughout the season, the number of
site treatments were added together for the two years of the pilot program and shown by each month
(Figures 1 and 2). As expected, the majority of the early season treatments that were performed were for
nuisance only species. Of the 175 site treatments performed over the course of the program, 50% were on
sites when both Culex and nuisance species were present, 31 % when Culex only species were present and
19% for nuisance-only species (Table 2).
Figure l Percentages of Site Treatments for Nuisance and Culex Larvae per Month, 2007
¦ % of Site Treatments for Culex-Only Species
of Site Treatments for Culex and Nuisance Species
of Site Treatments for Nuisance-Only Species
100%
lt7`Y
80% - - - 33% 32% 33%
60% - -17%
1t}Q36 1[?0% 7~e 37%
40% - - - -
20% - 3296
Apr May Jun Ju! Aug Sep Oct
Figure 2 Percentages of Site Treatments for Nuisance and Culex Larvae per Month, 2008
¦ %of5ite Treatments forCulex-Only Species
%of5ite Treatments forCulex and Nuisance Species
of Site Treatments for Nuisance-Only Species
100% 996 5%
80% 38% -
5196 GQ~6
60% 8390 - -fi3%
lU0%
40% - - -
11 54%
IM
~~%Q
Apr May lun Jul Aug Sep Oct
City of Boulder Pilot Program Report 7 ~tte mTa it
Table 2 Larval Treatment Summary by Month, 2007 and 2008 Combined
Percent
Month Apr May Jun Jul Aug Sep Oct Total of Total
Number of Site Treatments for Culex-
Only Species 0 0 5 14 22 13 0 54 31%
Number of Site Treatments for Culex and
0 1 9 36 26 16 0 88 50%
Nuisance Species
Number of Site Treatments for Nuisance-
Only Species Due to Pilot Program 6 7 5 5 8 2 0 33 19%
Total Site Treatments 6 8 19 55 56 31 0 175 100%
The number of sites breeding mosquito larvae and their treatments suggest that a substantial number of adult
nuisance mosquitoes would have become airborne had the pilot program not been implemented. The larval
surveillance data was used to estimate larval populations controlled during the pilot program vs. what would
have been controlled with only the standard WNV program. The estimates show that an average of over 39
million more mosquito larvae were controlled per year due to the pilot program (Table 3). Table 4 shows
the properties where treatments for nuisance-only mosquitoes occurred over the course of the pilot program.
Table 3 Comparison of Larval Populations Controlled During the Pilot Program vs. What Would
Have Been Controlled with the Standard WNV Pro ram
Pilot Program Standard WNV Increase Due to Pilot Program
Year
(Nuisance)1 Program (Culex)z Number Percent
2007 Estimated Larval Population Controlled3 254,321,825 185,711,800 68,610,025 27%
2008 Estimated Larval Population Controlled 25,193,240 15,635,227 9,558,013 38%
2-Year Average 139,757,532 100,673,514 39,084,019 28%
Notes:
1: The implemented program during 2007 and 2008
2: The back-calculated population if the Standard WNV Program had been conducted instead of the Pilot Program
3: Estimated Larval Populations were calculated by multiplying # per dip by 10 (each dip is approx. 1/10 of a sq. ft.) by the sq. ft. of breeding habitat
Table 4 Number of Treatments for Nuisance-Only S ecies Mos uitoes b Pr•o erty, 2007-2008
# of Treated Total # of Total # of
Property Name (Managing Department) Sites on Treatments Treatments 2-yr
Property in 20072 in 20082 Total
Boulder Reservoir (P&R) 6 9 12 21
Burke II (OSMP) 1 0 1 1
East Boulder Recreation Center (P&R) 3 0 3 3
Pleasantview Soccer Fields (P&R) 1 1 1 2
Sombrero Marsh (OSMP) 1 1 1 2
Stazio Ballfields (P&R) 1 2 2 4
'Total l3 13 20 33
Notes.
1: Total number of separate sites on property
2: Total number of treatments was obtained by combining the treatments from all of the separate breeding sites on
the property during the season
3.1.1 Evaluation of Nuisance Mosquito Larval Control Threshold
To evaluate the effectiveness of the 1 larva per dip larval control threshold, mosquito breeding data obtained
during the pilot program were analyzed. As shown in Table 5, during the two-years of the pilot program,
there were 81 times when habitat sites had nuisance-only larvae present at numbers under the 1 per dip count
threshold. Therefore, if the larval dip count threshold was lowered to the presence of nuisance larvae, there
would have been 81 more site treatments at 15 additional site locations within the pilot program area. This
City of Boulder Pilot Program Report s ~tterTail
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would have controlled an estimated additional 1 % of nuisance larvae in 2007 and an additional 11.9% of
nuisance larvae in 2008.
Table 5 Comparison of Site Treatments, Site Locations Treated, and Estimated Nuisance
Larval Po elation Controlled with Differin Di Count Thresholds, 2007-2008
Nuisance-Only Dip Count Threshold (q/dip) Difference Between ? 1.0 and >0 Thresholds
Year
21.0 2 0.5 > 0 Number Percent
2007
Number of Additional Site Treatments When
Only Nuisance Mosquitoes are Found 13 15 26 13 50.0%
Number of Additional Site Locations Treated
When Only Nuisance Mosquitoes are Found 8 9 13 5 38.5%
Number of Additional Larvae Controlled
68,610,025 68,904,025 69,281,060 671,035 1.0%
When Only Nuisance Mosquitoes are Founds
2008
Number of Additional Site Treatments When
Only Nuisance Mosquitoes are Found 20 30 88 68 77.3%
Number of Additional Site Locations Treated
12 17 27 15 55.6%
When Only Nuisance Mosquitoes are Found
Number of Additional Larvae Controlled
9, 558,013 10,017,069 10, 851, 636 1, 293, 624 11.9%
When Only Nuisance Mosquitoes are Founds
2-Year Average
Number of Additional Site Treatments When
Only Nuisance Mosquitoes are Found 16.5 22.5 57.0 40.5 71.1%
Number of Additional Site Locations Treated 10.0 13.0 20.0 10.0 50.0%
When Only Nuisance Mosquitoes are Found
Number ofAdditional Larvae Controlled
39,084,019 39,460,547 40,066,348 982,329 2.5%
When Only Nuisance Mosquitoes are Founds
r.'otes
1: Estimated larval populations were calculated by multiplying p per dip by 10 (each dip is approx 1/10 of a sq ft) by [he sq ft of breeding habitat
3.1.2 Results of the Mosquito Working Group Collaboration
A mosquito working group involving staff from OEA, OSMP, P&R, BCPH, and OtterTail was formed in
2007. The group discussed best management practices (BMPs) for mosquito control per the city IPM
process and looked at the management of specific city properties to ensure that all cultural and mechanical
controls for mosquitoes were being done within the confines of management priorities. An added benefit of
this working group was a better collaboration between both city departments and city and county staff for
overall mosquito management.
A direct result of that collaboration was the initiation of larval monitoring on the Xcel Energy property
adjacent to Leggett-Owen and Valmont reservoirs. Prior to the 2007 season, this private property had not
been monitored for mosquito larvae by the city or county. The mosquito working group initiated talks with
Xcel Energy to discuss access for the county mosquito contractor to map potential breeding sites, monitor for
both Culex and nuisance species, and to allow larval control for Culex and nuisance mosquito larvae. Over
the course of the city's pilot program, the county was able to perform 22 site inspections and 4 site
treatments on habitat areas within the Xcel Energy property. These treatments likely prevented a substantial
amount of mosquitoes from developing into adults and helped reduce trap numbers at the city's C 11 trap
(Figure 6), which is within a quarter of a mile of the Xcel Energy property.
3.2 ADULT MOSQUITO SURVEILLANCE AND CONTROL RESULTS
The four pilot program light traps collected a total of 6,093 mosquitoes during the 2007 season and 11,617
during the 2008 season. The total adults collected during the pilot program resulted in species within the
genus' Aedes and Ochlerotatus being the most abundant, followed by Culex, Culiseta, and finally
City of Boulder Pilot Program Report 9 ~tte mTa ~1
Coquillettida and Anopheles (Tables 6 and 7). There was an average of 85 adult mosquitoes per trap per
night in 2007 and an average of 138 adult mosquitoes per trap per night in 2008.
Table 6 Number of Adult Mosquitoes per Trap for the 2007 Season'
Culex s Ae. Oc. s Ano heles s Co uillettidia s Culiseta s verage
pp' / pp' p pp' q pp' pp' Total of All Total per
Trap Location (Name)
# % RAZ # % RA # % RA # % RA # % RA Trapnights Trapnight
Sombrero Marsh (H2) 298 14.5% 1,713 83.6% 0 0.0% 2 0.1% 36 1.8% 2,049 114
Stazio Ballfields (C31 399 17.8% 1,815' 80.9% 0 0.0% 6 0.3% 24 1.1% 2,244 125
Thorne Institute (C32) 285 50.2% 270 47.5% 2 0.4% 0 0.0% 11 1.9% 568 32
East Community Center (C13) 105 8.5% 1,116 90.6% 0 0.0% 1 0.1% 10 0.8% 1,232 68
Total of All Traps 1,087 17.8% 4,914 80.6% 2 0.03% 9 0.1% 81 1.3% 6,093 339
Average 272 1,229 0.5 2 20 1,523 85
Notes:
1: Season was May 8 to September 11 For a total of 72 trap nights
2: % RA =Percent Relative Abundance
Table 7 Number of Adult Mosquitoes per Trap for the 2008 Season'
Culexspp. Ae./Oc.spp. Anophelesspp. Coquillettidiospp. Culisetospp. verage
Trap Location (Name) Total of All Total per
# % RAZ # % RA # % RA # % RA # % RA Trapnights Trapnight
Sombrero Marsh (H2) 243 8.0% 2,768 90.8% 0 0.0% 0 0.0% 39 1.3% 3,050 145
5tazio Ballfields (C11 289 12.4% 2,033 87.0% 0 0.0% 0 0.0% 14 0.6% 2,336 111
Thorne Institute (C12) 239 4.7% 4,750 94.4% 0 0.0% 0 0.0% 45 0.9% 5,034 240
East Community Center (C13) 107 8.9% 1,084 90.6% 0 0.0% 0 0.0% 6 0.5% 1,197 57
Total of All Traps 878 7.6% 10,635 91.5% 0 0.00% 0 0.0% 104 0.9% 11,617 553
Average 220 2,659 0.0 0 26 2,904 138
Notes:
1.:season was April 26 to September 16 for a total of 84 trap nights
2: % RA =Percent Relative Abundance
To help show the possible effect of nuisance mosquito control within the pilot program area, season-wide
weekly trap counts of the six associated traps are presented in Figures 3 through 8. All but the two new
post-2006 traps (C12 and C13) have 2006 trap data included.
The traps in operation during 2006 (Figures 3 through 6) were examined to find any potential mosquito
population trends that differed from before and after the implementation of the pilot program's nuisance
control. Each trap had very high mosquito counts during portions of the 2006 season, when there was no
nuisance control. Although each trap had some relatively high mosquito counts compared to 2006 (Figures
3, 4, and 6), trap results suggest that the nuisance-controlled seasons of 2007 and 2008 had substantially
lower weekly population peaks during the full season of each year of the pilot program.
One trap does not fit into the overall trend of reduced mosquito population peaks. As shown in Figure 5, the
mosquito populations of trap BC-01 had a higher peak in 2008 than in 2006 or 2007. Trap BC-O1 is located
within a mile of several dozen sites that were not included in the pilot program. The most likely reason for
this 2008 August population spike was a period of high precipitation, thereby increasing the mosquito
breeding habitat at these sites. With those sites unable to be controlled for nuisance only inspections,
populations were able to escalate uncontrolled, thereby likely increasing area trap populations.
Figure 7 shows trap C-12 having a large mosquito population peak in 2008. Trap C-12 is located in close
proximity to the county's BC-32 trap on the east side of Sombrero Marsh. Since the marsh was treated for
mosquito larvae several times in July and August of 2008 and the two other nearby traps (H2 and BC-32) did
not have the high peak, the reason for the high population of trap C-12 is unknown. One possible reason for
the population peak is that the period of high precipitation in August may have created potential larval sites
City of Boulder Pilot Program Report l0 -OtterTail
Environmentalt
in areas of the nearby neighborhood that were not on city property (and; therefore, were not monitored or
controlled by the city), which produced large numbers of nuisance mosquitoes from the lack of larval control
on the nearby breeding habitats (Map A-2), correspondingly increasing the populations at Trap C-12.
Figure 3 Weekly Adult Trap Counts at Sombrero Marsh (Trap H2), 2006-2008
zsoo
k
2zso T
zooo
17so
a 1500
v
0
3 1250
v
~ 1000
w
0
750
E
Z 500
250
0 _ _ -
4126 5/i0 5/24 6/7 6/21 7/5 7/19 8/2 8/16 8/30 9/13
Week
2006 (No Larval Nuisance Control) 2007 (Larval Nuisance Control) 2008 (Larval Nuisance Control)
Figure 4 Weekly Adult Trap Counts at Sombrero Marsh (Trap BC-32), 2006-2008
zsoo ,
z2so
t zooo
m
17so ~ ~ ~ ~ ¦ ~
r
1500 ~ ¦ ¦ ¦ ¦ ¦ ¦
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a 1250
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E
3
z
500
250
0 - - - . - . _ - - ~ ~
4/26 5/10 5/24 6/7 6/21 7/5 7/19 8/2 8/16 8/30 9/13
-2006 (NO Larval Nuisance Control) 2007 (Larval Nuisance Control) -2008 (Larval Nuisance Control)
¦ 2006 ULV Spray (100 Threshold)i 2007 ULV Spray (250 Threshold) i ¦ 2008 ULV Spray (250 Threshold)1
Notes:
1 Boulder County weekly spray events that were triggered by either Trap BC-01 or BC-32 reaching the spraying threshold
City of Boulder Pilot Program Report 11 .OtterTail
Environmental r
Figure 5 Weekly Adult Trap Counts at Gapter Rd/Old Tale (Trap BC-O1), 2006-2008
2soo
zzso
4+
L
CO
c 2000
a
I- ,
w 1750 ~ ~ ! ! ! !
a
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1500 i ~ ~ ~ ~ r ¦
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o ~ 4
~ 1000
E '
Z 750 r1
500 `~1
250
_ ~
0 - f- - - _
4/26 5/10 5/24 6/7 6/21 7/5 7/19 8/2 8/16 8/30 9/13
-2006 (No Larval Nuisance Control) 2007 (Larval Nuisance Control) -2008 (Larval Nuisance Control)
¦ 2006 ULV Spray (100 Threshold) i 2007 ULV Spray (250 Threshold)i ¦ 2008 ULV Spray (250 Threshold)i
Notes:
1. Boulder County weekly spray events that were triggered by either Trap BC-Ol or BC-32 reaching the spraying threshold
Figure 6 Weekly Adult Trap Counts at Stazio Ballfields (Trap C11), 2006-2008
2500 `
2250
r 2000
m
~c
~ 1750
F-
a 1500
1250
1000
0 750
01 f
E 500
~ i
Z ~
250 ~ yYw
-
4/26 5/10 5/24 6/7 6/21 7/5 7/19 8/2 8/16 8/30 9/13
Week
-2006 (No Larval Nuisance Control) 2007 (Larval Nuisance Control) 2008 (Larval Nuisance Control)
City of Boulder Pilot Program Report 12 .(~tterTail
Environmental!
Figure 7 Weekly Adult Trap Counts at Thorne Institute (Trap C12), 2007-2008
2500
2250
Loo 2000
~c
Q 1
1750 !
~
v i
a 1500 r
v I
0
1250
a
° 1000
~ i
O
~ 750
~ 500 ~ I
z
250 i I~/
4/26 5/10 5/24 6/7 6/21 7/5 7/19 8/2 8/16 8/30 9/13
Week
- 2007 (Larval Nuisance Control) -~--2008 (Larval Nuisance Control)
Figure 8 Weekly Adult Trap Counts at EBCC (Trap C13), 2007-2008 ,
2500 i
2250
Y
m 2000
~C
a
1750
y
a 1500
v
1250 ~
3
~ 1000
° 750
v
~ 500
Z
250 y~f,,,~
0 - - _ - = - - - _
4/26 5/10 5/24 6/7 6/21 7/5 7/19 8/2 8/16 8/30 9/13
Week
2007 (Larval Nuisance Control) -2008 (Larval Nuisance Control)
City of Boulder Pilot Program Report 13 ~~el~a~f
1
The season-long average number of mosquitoes for each of the pilot program area traps are presented to help
evaluate the success of the pilot program's nuisance-larval control (Table 8). Four of the six traps had lower
total mosquito averages in both years of the pilot program than their 2006 averages.
Table 8 Average Number of Mosquitoes of the Pilot Program Area Traps, 2006-2008
Season-long Avg. # of Mosquitoes per Trap Might
Trap Location (Name) 2006 2007 2008
(Pre-Pilot)1 (Pilot)z (Pilot)Z
Sombrero Marsh (H2) 399 114 145
Sombrero Marsh (BC-32) 338 132 204
Stazio Ballfields (C11) 131 125 111
Thorne Insitute (C12) N/A 32 240
East Community Center (C13) N/A 68 57
Old Tale/Gapter Rd. (BC-01) _100 77 314
Notes:
1. Pre-pilot is without any larval nuisance-only control
2. Pilot is with larval nuisance-only control in many of the breeding habitats near the adult traps
3.3 EVALUATION OF THE EFFECTS OF THE PILOT PROGRAM ON COMPLAINT
NUMBERS
The high number of complaints from the city-owned revenue generating areas was one of the primary
reasons for the establishment of the pilot program. These complaints substantially decreased over the two
years of the pilot program. Although numbers weren't formally tracked before the 2007 season, city P&R
staff reported that there was a substantial decrease in complaints. City staff estimated that the number of
complaints went from an estimate of hundreds of complaints during the summer of 2006 to approximately a
dozen during each of the 2007 and 2008 seasons. In 2006 (before the pilot program), The Flatirons Golf
Course received over 50 written complaints and staff reported receiving dozens of verbal complaints on a
daily basis during May and June. Flatirons staff reported no written complaints and minimal verbal
complaints during the 2007 and 2008 season.
The complaints and mosquito populations from the Greenbelt Meadows and Gapter Road neighborhoods
remained relatively low throughout most of the two years of the program. However, complaints from these
areas substantially increased in August of 2008. These neighborhoods were located within or near the pilot
program area, but dozens of sites were within a mile radius of them that could not be treated for nuisance
only species. As previously discussed, the nuisance mosquitoes breeding in these nearby sites were a likely
reason for the August 2008 adult mosquito population spike found in the two nearby adult traps.
In response to the high number of complaints, the city and OtterTail met with residents of the neighborhoods
to explain the city's mosquito control plan policies, listen to the residents' concerns and evaluate the source
of the high nuisance counts. The city had OtterTail set an additional adult mosquito trap in the Greenbelt
Meadows neighborhood for the final four weeks of the mosquito season in an attempt to evaluate its
mosquito populations. As shown in Table 9, the additional trap captured high numbers of nuisance
mosquitoes during the last week of August. This data, along with the high population peaks found in traps
BC-01 and C 12 (Figures 6 and 7), helped confirm the high amount of nuisance mosquito activity in the area
during August of 2008.
Incidentally, the trap results shown in Table 9 also suggest that the city's standard WNV program is
accomplishing its goal in protecting the public health with only 2 Culex (or 0.2%) found out of 1,311
nuisance mosquitoes (or 99.8%).
City of Boulder Pilot Program Report 14 AtterTail
Environmental t
Table 9 Trap Counts for Greenbelt Meadows Neighborhood Temporary Trap, 2008
Number of Nuisance Number of Culex Percent Percent
Date Trap Total
Species Mosquitoes Species Mosquitoes Nuisance Culex
8/26 1,311 2 99.8% 0.2% 1,313
9/2 251 3 98.8% 1.2% 254
9/9 262 2 99.2% 0.8% 264
9/16 37 2 94.9% 5.1% 39
Although the data suggests that the pilot program was not successful incompletely alleviating the high
number of nuisance mosquitoes and complaints from the Greenbelt Meadows and Gapter Road
neighborhoods, there was some improvement. The mosquito populations and complaints from these
neighborhoods remained at relatively low levels until the nuisance populations increased in August of 2008.
Furthermore, it is very likely that the addition of those nearby sites into the pilot program would have
substantially reduced the nuisance population of that August spike in and around the Greenbelt Meadows
area. Data from the 2007 and 2008 seasons of the WNV program were analyzed to find the amount of
nuisance breeding that occurred in these sites and how they likely contributed to the nearby neighborhoods'
high nuisance mosquito populations.
As shown in Table 10, there was a total of 63 times during the two year pilot program that nuisance-only
mosquitoes were found present within these habitat sites at 1 per dip or greater without any control
occurring. During 2008, there was a total of 56 times that nuisance-only mosquito larvae were found present
at larval dip counts above the 1 larva per dip treatment threshold. Of these 56 times, 20 occurred during the
month of August. The nuisance-only larvae occurrences at these sites correspond with the high adult trap
counts seen in the area traps in 2008. These results indicate that if nuisance control had been performed on
these larval sites, the area adult mosquito populations likely would not have been as high as they were in
August of 2008.
An estimate of over 284 million additional mosquitoes would have been controlled had these sites been
treated during the nuisance-only occurrences during the 2008 season. The results indicate that the addition of
these 35 habitat sites into the pilot program would help alleviate the high mosquito populations and
residential complaints from the Greenbelt Meadows and Gapter Road neighborhoods.
City of Boulder Pilot Program Report 15 Dtte mTaa
j
- - - - -r-~
Table 10 Comparison of Larval Surveillance and Control Activities at 35 Habitat Sites Within One
Mile of the Greenbelt Meadows and Gapter Rd. Neighborhoods Had They Been Included in
the Pilot Pro ram vs. What Was Performed With the Standard WNV Pro ram, 2007-2008
Had the 35 Standard WNV Increase Had the 35
Year Sites Been Program Sites Been Added3
Addedl (Culex)Z Number Percent
2007
Number of Site Treatments 31 24 7 22.6%
Number of Site Locations Treated 12 10 2 16.7%
Total Treated Acreage 17 1.6 15.4 90.6%
Pounds of Bti Used4 85 8 77 90.6%
Estimated Number of Larvae Controlleds 36,520,625 5,966,365 30,554,260 83.7%
2008
Number of Site Treatments 65 9 56 86.2%
Number of Site Locations Treated 23 7 16 69.6%
Total Treated Acreage 109 0.6 108.4 99.4%
Pounds of Bti Used4 545 3 542 99.4%
Estimated Number of Larvae Controlleds 284,556,128 4,045,750 280,510,378 98.6%
2-Year Average
Number of Site Treatments 48.0 16.5 31.5 65.6%
Number of Site Locations Treated 17.5 8.5 9.0 51.4%
Total Treated Acreage 63.0 1.1 61.9 98.3%
Pounds of Bti Used4 315.0 5.5 309.5 98.3%
Estimated Number of Larvae Controlleds 160,538,376 5,006,058 155,532,319 96.9%
Ncstes
1: Results if the 35 sites had been included in the Pilot Program, allowing larval control during nuisance-only occurences
2: Actual results due to the 35 sites being in the Standard WNV Program program and not added to the Pilot Program
3: Increase had the 35 sites been included in the Pilot Program allowing larval control during nuisance-only occurences
4: Amount of Bti used when applied at the typical 5 lbs. per acre application rate
5: Estimated larval populations were calculated by multiplying # per dip by 10 (each dip is approx. 1/10 of a sq. ft) by the sq. ft. of breeding habitat
3.4 EVALUATION OF THE EFFECT OF INCREASING THE SPRAY THRESHOLD ON
ADULT SPRAYING FREQUENCY
One of the goals for doing larval nuisance control in the pilot program area was to reduce the potential for
pesticides to drift onto city property from the county's adult ULV adulticide applications. As part of the
negotiations that enabled the approval of the pilot program, the Boulder County commissioners and BCPH
agreed to raise the thresholds that trigger an adult spray event surrounding the pilot program from the
historical threshold of 100 mosquitoes per trap night to 250.
Three traps that were in or near the pilot program were assigned the higher threshold (Map A- 2). The data
from traps BC-O1 and BC-32 were used in combination by BCPH to aid in the weekly decision whether or
not to spray the Gapter Road/Baseline Heights neighborhood of Boulder. If either trap was above the
threshold during a given week, then areas of the neighborhood would be sprayed. The data from trap BC-43
was used by BCPH to aid in the weekly decision to spray the San Lazaro Mobile Home Park neighborhood
of Boulder.
City of Boulder Pilot Program Report 16 ~tterTail
Environmental
Table 11 Comparison of the Number of County ULV Spray Applications Using the Pilot
I'ro ram's 250 Threshold vs. the Previous Pre-Pilot Threshold of 100
Year 250 Threshold 100 Threshold Decrease Due to Increase to 250 Threshold
(Pilot Program)1 (Previous)2 Spray Events Linear Miles Sprayed3 Pesticide Gallons° Percentage
2007
Baseline Heights Area Traps (BC-O1 and BC-32) 2 7 5 63.8 4.7 71.4%
San Lazaro Area Trap (BC-43) 8 10 2 3.2 0.2 20.0%
Areas Combined 10 17 7 67.0 4.9 41.2%
2008 0.0
Baseline Heights Area Traps (BC-Ol and BC-32) 9 11 2 25.5 1.9 18.2%
San Lazaro Area Trap (BC-43) 4 12 8 12.8 0.9 66.7%
Areas Combined 13 23 10 38.3 2.8 43.5%
2-Yea r Average 0.0
Baseline Heights Area Traps (BC-01 and BC-32) 5.5 9.0 3.5 44.7 3.3 38.9%
San Lazaro Area Trap (BC-43) 6.0 11.0 5.0 8.0 0.6 45.5%
Areas Combined 11.5 20.0 8.5 52.7 3.9 42.5%
Notes:
1: The number of spray events occurring if spraying occurred each time [he 250 mosquitoes per trap per trap night threshold was reached due to the Pilo[ Program threshold
2: The number of spray events occurring if spraying occurred each time the 100 mosquitoes per trap per trap night threshold was reached without the Pilot Program threshold
3: Calculated by multiplying the number of spray events not conducted by the average route distance; average route distance was calculated from 2007-200g BCPH spray events data
4: Pesticide gallons were estimated using a typical application rate of 2 35 ounces per minute applied at 15 MPH for an undiluted adultcide
Based on the trap results, there were 23 times the county would have sprayed these areas during the pilot
program compared to the 40 times they would have sprayed without the pilot program threshold (see Table
10). This represents an average reduction of approximately 43% less adulticide spraying each year. The
average amount of linear miles sprayed and amount of pesticides used also decreased by approximately 43%,
with estimated amounts shown in Table 11. Although the majority of these spray events were likely avoided
simply due to the increased threshold, it can be assumed that Bti treatments for nearby nuisance larvae helped
lower the area adult populations and the corresponding trap counts (as discussed in Section 3.2).
3.5 EVALUATION OF TRAP BC- 43 TO ASSESS THE EFFECTS FROM NOT
CONDUCTING NUISANCE LARVAL CONTROL ON NEARBY SITES
During the site selection process, thirteen larval sites surrounding the San Lazaro Mobile Home Park (San
Lazaro MHP) were dropped from the pilot program, thereby excluding the ability to control for nuisance-
only occurrences of mosquito larvae at these sites (Map A-2). Trap BC-43 is located within San Lazaro
MHP and is used by the county to monitor the area's adult mosquito populations and to aid in the weekly
decision of whether or not to spray the neighborhood. Data from the 2007 and 2008 seasons of the WNV
program were analyzed to find the amount of nuisance breeding that occurred in these sites and how they
might have contributed to the mosquito populations of trap BC-43 and the corresponding county ULV
spraying frequency.
As shown in Table 12, there was a total of 9 times during the two-year pilot program that nuisance-only
mosquitoes were found present within the 13 habitat sites at the 1 per dip or greater pilot program threshold,
which would have resulted in control occurring had the sites been in the program. This results in an estimate
of over 27 million nuisance mosquitoes that were allowed to live, with a portion of those maturing into adults
to become part of the area's adult mosquito populations.
Furthermore, as seen in Figure 9, when the nuisance-only larval occurrences from the 13 sites are compared
with the county ULV sprays during the pilot program, it shows 4 ULV spray events that potentially could
have been avoided had the sites been treated for nuisance-only larvae occurrences.
In 2007, the county performed ULV spray events during the week of August 9`'' and the week of August 23ra
Nuisance-only mosquitoes were found breeding at one of the larval sites on August 7a', but were not
controlled since the site was not part of the pilot program. This non-treatment allowed an estimated 3.2
million mosquitoes to potentially mature into adults to become a portion of the local mosquito populations.
City of Boulder Pilot Program Report 17 Ottet`I'aa
1
It is likely that these mosquitoes caused an increase in the trap BC-43 populations, causing it to exceed the
ULV spray triggering threshold during the weeks of August 9th and August 23rd
The county also performed ULV spray events during the week of August 2°d and the week of August 9`h in
2008. Nuisance-only mosquitoes were found breeding in nearby larval sites on July 26`'' and August 4th.
Since the larvae were not treated, due to those sites not being included in the pilot program, there was an
estimated 201,000 mosquitoes that were allowed to mature into adults to become a portion of the local
mosquito populations. As in 2007, these mosquitoes likely caused the adult populations to exceed trap B-
43's triggering threshold, resulting in two county ULV spray events.
The results indicate that the addition of these 13 habitat sites into the pilot program would have likely
decreased mosquito populations and the number of county ULV spray events in San Lazaro MHP. Had the
nuisance-only larvae been controlled at these sites, there likely would have been 4 less ULV spray events
performed by the county. This would have prevented 9.9 linear miles of ULV pesticide spraying from
occurring (which would equal approximately 92 ounces of pesticides when used at a typical application rate).
Table 12 Comparison of Larval Surveillance and Control Activities at 13 Habitat Sites Within One
Mile of the San Lazaro MHP Neighborhood Had They Been Included in the Pilot Program
vs. What Was Performed With the Standard WNV Pro ~ratn, 2007-2008
Had the 13 Standard WNV increase Had the 13
Year Sites Been Program Sites Been Added3
Addedl (Culex)2 Number Percent
2007
Number of Site Treatments 8 5 3 37.5%
Number of Site Locations Treated 4 4 0 0.0%
Total Treated Acreage 1.9 0.2 1.7 89.5%
Pounds of Bti Used4 9.5 1 8.5 89.5%
Estimated Number of Larvae Controlleds 6,777,800 90,300 6,687,500 98.7%
2008
Number of Site Treatments 13 7 6 46.2%
Number of Site Locations Treated 6 3 3 50.0%
Total Treated Acreage 5.3 0.2 5.1 96.2%
Pounds of Bti Used4 26.5 1 25.5 96.2%
Estimated Number of Larvae Controlleds 20,500,020 106,500 20,393,520 99.5%
2-Year Average
Number of Site Treatments 10.5 6.0 4.5 42.9%
Number of Site Locations Treated 5.0 3.5 1.5 30.0%
Total Treated Acreage 3.6 0.2 3.4 94.4%
Pounds of Bti Used4 18.0 1,0 17.0 94.4%
Estimated Number of Larvae Controlleds 13,638,910 98,400 13,540,510 99.3%
(votes:
1: Results if the 13 sites had been included in the Pilot Program, allowing larval control during nuisance-only occurences
2: Actual results due to the 13 sites being in the Standard WNV Program program and not added to the Pilot Program
3: Increase had the 13 sites been included in the Pilot Program allowing larval control during nuisance-only occurences
4: Amount of Bti used when applied at the typical 5 lbs. per acre application rate
5: Estimated larval populations were calculated by multiplying # per dip by 10 (each dip is approx. 1/10 of a sq fti by the sq. ft of breeding habitat
City of Boulder Pilot Program Report l8 ~tteYTall
Environmental
Figure 9 Weekly Adult Trap Counts at San Lazaro MHP (Trap BC-43), County ULV Spray
Events, and Nuisance-Only Larval Occurrences at Sites Within One Mile of the Trap,
2007-2008
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2007 Estimated # Nuisance-Only Larvae ~ ~ 2008 Estimated # Nuisance-only Larvae 1
2007 # of Adul[ Mosquitoes - 2008 # of Adult Mosquitoes
2007 ULV Spray (250 Threshold) Z ¦ 2008 ULV Spray (250 Threshold) Z
Notes:
1: Estimated population not controlled due to bypassing larval treatment due tonuisance-only otturrences at any of the 13 sites not
included in Pilot Program; Estimated Larval Populations were obtained by multiplying # per dip by SO (each dip is approx. 1/10 of a
sq. ft.) by the sq. ft. of the breeding area
2- Boulder County weekly spray events that were triggered by Trap BC-43 reaching the spraying threshold
3.6 EVALUATION OF POTENTIAL ENVIRONMENTAL IMPACTS OF PESTICIDE
USE
3.6.1 Potential Long-Term Impacts of Bti Treatments on Biota
As part of the pilot program, the city wanted to perform studies to find the potential long term impacts of
treating area wetlands with Bti for mosquito control. In 2007, the working group developed a plan to
conduct a macroinvertebrate biodiversity study of all the wetland breeding habitats within the city's WNV
program. This would consist of a taxa gathering effort at 3 different times of the year to determine the
diversity value of each habitat to assess what the true impact is on habitats being treated with Bti. However,
after receiving cost estimates, the studies were deemed to be cost prohibitive.
While no strong impact study was performed within the program area, past literature reviews (see the 2006
City of Boulder West Nile Virus Mosquito Management Plan) have shown that Bti has little or no direct
effects to non-target organisms and wildlife. As discussed in the 2006 management plan, research and field
City of Boulder Pilot Program Report 19 -O~te mTa it
experiments have shown that Bti has no toxic effects on beneficial and predacious arthropods or insects (such
as caddisflies, mayflies, stoneflies, damselflies, dragonflies and water beetles) or aquatic invertebrates and
vertebrates. However, studies also indicate that Bti may cause a reduction in dipteran density and
chironomid richness. These results indicate a change in wetland function and indirect adverse effects are
likely for vertebrate predators of chironomids and mosquitoes (such as waterfowl). Therefore, it is assumed
that the effects of removing mosquito larvae is by far the biggest impact to the food chain, as that removes
the largest biomass from many wetlands and also reduces aquatic biodiversity by lowering the predaceous
biota (fish, predaceous diving beetles, dragonfly nymphs, etc.) that prey upon them.
There is no doubt that bats and birds would also feed on the mosquitoes that are being eliminated (and would
otherwise emerge as adult mosquitoes) but determining the exact extent of the effect on the environment with
any accuracy would be next to impossible due to natural biological variability, migrations, etc. The city staff
also consulted with several bird and bat experts who also concluded this would be an unrealistic task.
3.6.2 Potential Effects of ULV Spraying on fhe Environment
The county currently performs adult mosquito spraying using ULV spraying techniques with awater-based
product with a pyrethroid as the active ingredient. These products cause rapid knockdown of adult
mosquitoes and are mixed with a synergist compound, piperonyl butoxide (PBO), which enhances the
effectiveness of the active ingredient. Pyrethroids and PBO, per the city of Boulder's IPM policy, are less
acceptable than Bti treatments (larval control) due to their increased ecological impacts to non-target and
aquatic organisms.
In an effort to better understand the potential effects of the county ULV spraying, the city of Boulder
coordinated with OtterTail and the United States Geological Survey (USGS) to perform water quality testing
at two locations within the city. The USGS designed a study to sample two locations, one on South Boulder
Creek and one on Boulder Creek. The Boulder Creek location was chosen due to the fact that it had
historically been sprayed with ULV applications of pyrethroids on a frequent basis for mosquito control.
Since pyrethroids are also used in other pest control applications besides those that are performed for
mosquito control, the South Boulder Creek location was chosen to collect samples to detect any potential
background levels of the pesticide in an area stream that did not receive nearby ULV spraying for mosquito
control.
During the summer of 2007, USGS placed sediment collectors in Boulder Creek and South Boulder Creek.
Each creek had a collector placed in an area upstream and a collector placed in an area downstream of the
testing and control locations. The sediment collectors were designed to collect sediments containing any
pesticides that settled out of the water column. The USGS removed the sediment collectors at the end of the
2007 season and the samples from the collectors were then frozen and stored for later analysis. As of
January 2009, the USGS has not analyzed the samples for the study. The USGS expects to have the study
complete and the results available in the spring of 2009.
In addition to the sediment sampling, the city and OtterTail also collected water quality grab samples before
and after a county spray event along South Boulder Creek. The purpose of the grab samples was to collect
any pesticides that potentially drifted into the creek immediately after a ULV spray application. Samples
were taken before the spray application, one-hour after the spray application and again on the morning-after
the application at both upstream and downstream locations. Twelve grab samples were provided to the
USGS for water quality analysis during the summer of 2007. The samples were stored by the USGS for later
analysis, but unfortunately the USGS was unable to analyze them within the appropriate timeframe needed
for the testing procedure, therefore the samples were discarded without being analyzed.
City of Boulder Pilot Program Report 20 .1~tteYTai1
Environmental!
4.0 SUNMIUTARY OrF PILUT PRUGRAIVI RE5ULT5
The results of the pilot program indicate that it was successful in many areas of the program. As discussed in
Section 3.0, the number of treatments by the city for nuisance-only species of mosquitoes over the two-year
period increased by 33 (19%), which increased the amount of acreage treated by 11 acres (30%) and the
amount of Bti applied by 57 pounds (30%). These increases are due to the pilot program enabling OtterTail
to treat for nuisance-only mosquitoes. In addition to the city's nuisance treatments, the formation of the
Mosquito Working Group allowed the county's mosquito control contractor to treat the larval habit within
the Xce] Energy property 4 times over the course of the pilot project, further reducing mosquito populations
within the pilot program project area.
The adult surveillance data discussed in Section 3.0 suggests that the city and county larval control efforts
had an impact on the pilot program area's adult mosquito populations. While there were still periods of high
adult populations, the overall trends from the majority of the traps show a decrease in nuisance mosquito
populations from 2006. Although it is difficult to directly compare the trap numbers from 2006, which was a
season that had above average nuisance mosquito activity, to the numbers found during the 2007 and 2008
seasons, overall trap results show a pattern of decreased mosquito populations during the two years of the
pilot program. The combination of lower trap numbers and a higher triggering threshold number from the
three county traps around the project area decreased the potential county ULV spray applications by 43%.
Although the majority of these spray events were likely avoided simply due to the increased threshold, it can
be assumed that Bti treatments for nearby nuisance larvae helped lower the area adult populations and the
corresponding trap counts (as discussed in Section 3.4).
The number of complaints from the city-owned revenue generating areas, which was one of the primary
reasons for the establishment of the pilot program, decreased over the past two seasons. The complaints
went from the city receiving hundreds during the summer of 2006 to approximately a dozen during each of
the 2007 and 2008 seasons. While there was a substantial decrease in revenue-generating area complaints,
the city had a large increase in complaints from residents of the Greenbelt Meadows and Gapter Road
neighborhoods during August of 2008. The complaints corresponded with a rise in nuisance mosquito
populations, after a high amount of precipitation filled many of the nearby mosquito breeding sites that were
not include in the pilot program. Since these habitat sites could not be treated for nuisance only mosquitoes,
the larvae were allowed to mature into adults and were likely a primary contributor to the high trap counts
and complaints in the area.
City of Boulder Pilot Program Report 21 .~~te mTaa
j
5.0 PIL~]T PRaGRAIIA OPTIONS
OPTION 1: CONTINUE THE PILOT PROGRAM WITH NO CHANGES
As discussed in Section 3.0, the results from the pilot program indicate that it was successful in decreasing
adult mosquito populations around the city's revenue-generating properties and in decreasing the number of
county ULV pesticide spray applications. Although the data also suggests that the pilot program was not
successful in completely alleviating the high number of nuisance mosquitoes and complaints from the
Greenbelt Meadows and Gapter Road neighborhoods, there was some improvement. The mosquito
populations and complaints from these neighborhoods remained at relatively low levels during the pilot
program until the nuisance populations increased in August of 2008. Even though the residential
neighborhoods continued to experience periods with high nuisance mosquito populations, the success of
decreasing the nuisance mosquito activity and complaints from patrons at the city owned revenue-generating
areas could alone justify the continuation of the pilot program.
OPTION 2: LOWER THE LARVAE PER DIP THRESHOLD NUMBER REQUIRED FOR NUISANCE
MOSQUITO CONTROL AT SITES WITHIN THE PILOT PROGRAM
One method that would likely increase the success rate of reducing adult nuisance population numbers within
and around the pilot program area is to decrease the larval threshold number that is required before larval
control can be performed upon a site. While controlling at a threshold number of 1 larvae per dip prevents a
large amount of mosquito larvae from maturing into adult mosquitoes, there is still a substantial number of
adult mosquitoes that can be produced from habitats with a larval dip count below 1 per dip. Table 13
illustrates the number of mosquitoes that can be produced from a half acre site with differing dip count
thresholds during a breeding cycle. As show, a half acre habitat site is estimated to produce 21,780
mosquitoes with a larval dip count of just 0.1 larvae per dip and as many as 196,020 mosquitoes at 0.9 per
dip. Under the current pilot program threshold number of greater than 1 per dip, 196,020 mosquitoes would
be allowed to live, with a portion of those maturing into adults to become a portion of an area's adult
mosquito populations. As discussed in Section 3.1.1, using breeding from the pilot program, an estimated
1,653,364 more nuisance mosquitoes would have been controlled during the program by lowering the dip
count threshold to presence of larvae.
Table 13 Theoretical Larval Po ulations Based on Differin Di Counts in 0.5 Acre Habitat
# Larvae per Dip Habitat Acres Estimated Larval Populationl
> 0.0 0.5 0
> 0.0 0.5 21,780
> 0.2 0.5 43,560
> 0.3 0.5 65,340
> 0.4 0.5 87,120
> 0.5 0.5 108,900
> 0.6 0.5 130,680
> 0.7 0.5 152,460
> 0.8 0.5 174,240
> 0.9 0.5 196,020
> 1 0.5 217,800
Notes:
1: Estimated Larval Populations were obtained by multiplying p per dip by 10 (each dip is approx 1/10 of a sq, ft.)
by the sq. ft. of the breeding area
City of Boulder Pilot Program Report 22 ~tterTail
Environmental s
OPTION 3: EXPAND THE PILOT PROGRAM AREA TO INCLUDE ADDITIONAL SITES THAT
WOULD FURTHER REDUCE MOSQUITO POPULATIONS IN THE GREENBELT
MEADOWS AND GAPTER ROAD NEIGHBORHOODS
Even though there was a substantial decrease in the revenue-generating area complaints, the city had a large
increase in complaints from residents of the Greenbelt Meadows and Gapter Road neighborhoods during
August of 2008. As discussed in Section 3.3, the likely reason the pilot program was not more successful in
lowering the adult mosquito populations and complaints in these areas was due to a large number of nearby
breeding sites that were not included in the pilot program. There were 35 breeding sites within a one mile
radius of these neighborhoods that were being controlled for Culex mosquitoes under the WNV program, but
not for nuisance-only occurrences.
OPTION 4: MAINTAIN THE PILOT PROGRAM, BUT REDUCE BCPH's ADULTICIDE THRESHOLD
BACK TO 100
OPTION 5: DISCONTINUE PILOT PROGRAM
As discussed in Section 3.6, due to financial constraints, the City was unable to perform any biological
monitoring studies to determine the potential long term impacts of treating area wetlands with Bti for
mosquito control. Since these studies were not performed and the potential impacts on local wetlands were
not determined, treatment for nuisance-only mosquitoes should be discontinued.
City of Boulder Pilot Program Report 23 .OtterTail
Environmental
Appendix A; Ma s
Map A-1: Pilot Program Larval Site Locations
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2008 Larval Sites - y---c cw~~.~ro cr.o-~7; ~ _ `ir/
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Urban Parks
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e9_•, 'JJ City Llmlts
OtterI'ail
City of Boulder Pilot Program Report Appendix A j;m~irunmcnl+d
Map A-2: Pilot Program Adult Trap Locations
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Nursancn Mosyurto Adull irapa 1Juisa neo Mos quilo PiIW Projttl Larval Srtas Urban Parke
;~,ah. Trap; IOd6 Larval Silas ~ Crty Limlls
ir}'Tr d.~s r'n.+crrriry Op?n Spa~_e and Muuntein Parke Properly ~r ~ OtterTail
Ibn~e Co .:rve-.ss Fai:•r! ~ r~
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4e:Nw~rvr Fairr•w
Otterl~iil
City of Boulder Pilot Program Report Appendix A F:nvirunmcnlal