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West Nile Virus Vector Mosquito Larval Monitoring and Surveillance - 2011
February 2012
Watershed Monitoring and Reporting Ecology Division
Acknowledgements
TRCA recognizes the contributions from our staff including Sarah Scharfenberg for her technical
assistance with field sampling and larval rearing; as well as Ming Guo and Jason Tam for their
role in WNV database development and GIS mapping. We would also like to thank our regional
public health partners for providing us with invaluable data and their assistance in larvicide
treatment applications. Art Augenas from the Peel Region Public Health is acknowledged for
providing QA/QC on mosquito larvae identification.
The West Nile Virus Surveillance and Monitoring Program is a part of TRCA’s Regional
Watershed Monitoring Program. It is funded by the following partners:
Report prepared by: Jessica Fang, Aquatic Biologist Watershed Monitoring and Reporting Ecology Division Reviewed by: Scott Jarvie, Manager
Watershed Monitoring and Reporting Ecology Division
This report may be referenced as:
Toronto and Region Conservation Authority (TRCA). 2012. West Nile Virus Vector Mosquito Larval Monitoring and Surveillance – 2011. 18 pages + appendices.
Executive Summary
West Nile virus (WNV) is primarily a bird pathogen that first appeared in Ontario in 2001. Humans
and other mammals are incidental or “dead-end” hosts. Evidence suggests that two key vector
mosquito species, Culex pipiens and Culex restuans, are primarily responsible for spreading the
disease to humans in Ontario (Kilpatrick et al. 2005; Hamer et al. 2009). The level of WNV activity
and risk of exposure depends on the numbers of WNV bird hosts and WNV positive mosquitoes
in a given year. The vector population dynamics change from year to year, jurisdiction to
jurisdiction and are influenced by various biological and environmental factors. WNV
management strategies undertaken collectively by the provincial and regional health agencies in
Ontario focus on prevention and control measures.
The Toronto and Region Conservation Authority (TRCA) established its WNV vector mosquito
larval surveillance and monitoring program in 2003 as a measure of due diligence and at the
request of its regional public health partners. A variety of wetland habitats on TRCA properties
such as marshes, woodland pools and ponds have been considered potential mosquito
breeding habitats. However, monitoring data collected by TRCA since 2003 have shown that
healthy functioning wetlands generally do not support large Culex pipiens and Culex restuans
populations. Occasionally, isolated pockets of water with high densities of vector mosquitoes
have been found on TRCA properties; these findings signify the importance of larval mosquito
monitoring, so that these potential sites of concern can be identified and the appropriate control
measures can be taken.
TRCA’s WNV program has a three-pronged approach including public education and
communication, collaboration with regional public health units, and larval mosquito monitoring.
Public education activities in 2011 continued to focus on WNV related information distribution
and to address public and staff inquires on WNV and standing water complaints. In 2011, TRCA
received seven standing water complaints associated with TRCA properties. The complaints
were addressed according to TRCA’s Standing Water Complaint Procedure; none of the
complaint investigations resulted in larvicide application. Collaboration with regional heath units
in 2011 required TRCA staff to share WNV related information, attend regional health WNV
committee meetings, and provide mosquito larvae identification training to regional health staff.
Larval mosquito surveillance and monitoring was undertaken in 46 sites across TRCA jurisdiction
from May 30th to September 6th, 2011.
A total of 37 wetlands and 9 stormwater management ponds (SWMPs) were sampled using a
standard mosquito dipper. Larval mosquito sampling in 2011 yielded a high number of larvae
(n=8233) of which 6784 larvae were collected from the wetlands and 1449 were collected from
the SWMPs. Approximately 10% of larvae were not identified due to premature mortality during
the rearing process. Less than 25 % of mosquito species found in Ontario are considered WNV
vector species. WNV vector mosquito species refer to the species that are capable of carrying
and transmitting the virus from one host to another. The species that do not transmit the virus
are referred to as non-vector species. A total of 13 mosquito species were found during the 2011
sampling season including 5 non-vector species (Anopheles earlei, Culex territans, Culiseta
inornata, Psorophora ferox, and Uranotaenia sapphirina) and 8 WNV vector species (Aedes
vexans, Anopheles punctipennis, Anopheles quadrimaculatus, Culex pipiens, Culex restuans,
Culex salinarius, Ochlerotatus japonicus, and Ochlerotatus trivittatus). The most abundant
species in terms of presence was Culex territans which inhabited 39 of the 46 (85%) sampling
sites. The two key vector, Culex pipiens and Culex restuans, were found in 17 sites and 10 sites
respectively.
In the wetlands, 53.9% of larvae were non-vector species and 46.1% were vector species. The
non-vector, Culex territans (n= 3175; 53.1%) was the dominant species in terms of abundance
and presence. The two key WNV vectors Culex pipiens and Culex restuans represented 31.4%
and 2.6 % of the larvae collected respectively. Culex pipiens was the predominant vector species
found in the wetlands. Grenadier Pond in High Park, Lacey’s Pond in Altona Forest, and Goldfish
Pond in Tommy Thompson Park were identified as hotspots for Culex pipiens in 2011.
A total of 1449 larvae were collected in the SWMPs representing 17.5% of all larvae collected in
2011. Similar to the results from previous years, vector species comprised 83.5% of the
mosquito larvae collected, while Culex territans, the only non-vector species made up the
remaining 16.5%. Culex pipiens was the predominant species (n=1015; 73.6%) found in the
SWMPs. The other key vector species Culex restuans represented 3.8% (n=52) of the larvae
collected in the SWMPs. SWMP 279.1 in Durham and L’Amoreaux Park North Pond in Toronto
were identified as hotspots for Culex pipiens, and these two sites were larvicided by the Durham
Region Public Health and the City of Toronto Public Health respectively.
In conclusion, the results from the 2011 sampling season supported the findings from the
previous TRCA studies. It showed that wetlands do not generally support high densities of WNV
vector larvae, and SWMP sampling yielded low numbers of mosquito larvae overall. Only 6 of the
167 (3.6%) collected samples had high densities of vector mosquito larvae that warranted
control measures. However, WNV “hotspots” continue to occur and the locations vary from year
to year within TRCA’s jurisdiction. The most important objective of TRCA’s WNV monitoring
program is to reduce WNV risk to residents and conservation area user. In 2011, this objective
was met through identifying WNV hotspots and following-up with appropriate intervention
measures, through public education and communication, and through collaboration with TRCA’s
regional public health partners.
Table of Contents
1. Introduction ................................................................................ 1
2. Larval Mosquitoes Monitoring Methods .................................. 2
2.1 Larval Collection and Identification ............................................................2
2.2 WNV Risk Assessment ................................................................................3
3. Public Education and Communication ..................................... 5
3.1 Distribution of WNV Educational Materials ................................................5
3.2 Standing Water Complaint Procedure .......................................................5
4. Collaboration with Regional Health Units ................................ 7
5. Results and Discussion............................................................. 7
5.1 Mosquito Larval Density .............................................................................7
5.1.1 Wetlands ...............................................................................................8
5.1.2 Stormwater Management Ponds ...................................................... 10
5.1.3 Interspecies competition between key vector species .................... 12
5.2 Risk Assessment and WNV Vector Hotspot Identification ..................... 12
5.2.1 Wetlands ............................................................................................ 12
5.2.2 Stormwater Management Ponds ...................................................... 13
5.2.3 Standing Water Complaint Sites ....................................................... 13
5.3 Mosquito species composition and in-situ water quality........................ 15
6. Conclusions and Recommendations ..................................... 15
7. References ............................................................................... 17
List of Figures
Figure 1. Location of wetland and stormwater management pond monitoring
sites, 2011. .................................................................................................... 4
Figure 2. TRCA Standing Water Complaint Procedure .......................................... 6
Figure 3. Vector and non-vector mosquito larvae composition in wetlands from
2006 – 2011. ................................................................................................. 8
Figure 4. Mosquito species composition in wetlands, 2011. ................................. 9
Figure 5. Vector and non-vector mosquito composition in stormwater
management ponds, 2006 – 2011. ............................................................ 10
Figure 6. Mosquito species composition in stormwater management ponds,
2011. ........................................................................................................... 11
List of Tables
Table 1. List of WNV vector hotspots in wetlands, 2011. ..................................... 12
Table 2. List of WNV vector hotspots in stormwater management ponds, 2011. 13
Table 3. Results of standing water complaint investigation, 2011. ...................... 14
Appendices
Appendix A. Total Reported West Nile Virus Clinical Cases in Canada
Appendix B. WNV vector species of concern in Ontario
Appendix C. Overall summary the 2011 WNV monitoring season results
Appendix D. Risk ranking of wetland sites in 2011
Appendix E. Risk ranking of stormwater management pond sites in 2011
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
1
1. Introduction
West Nile virus (WNV) is primarily a bird pathogen that first appeared in Ontario in 2001. The
disease is transmitted to humans by mosquitoes that become infected by feeding on infected
birds. Humans are considered to be incidental or “dead-end” hosts whereby although humans
can be infected by the virus, humans do not spread the disease. For those people who become
infected, the majority will have no symptoms or only mild flu-like symptoms. Severe cases of
WNV, including the development of meningitis and encephalitis, are extremely rare but can be
fatal. In Canada, the numbers of human WNV cases fluctuate from year to year (Appendix 1),
driven by environmental and biological factors. In 2011, a total of 101 human cases were
reported in Canada; Ontario reported 64 cases, and Quebec reported 37 cases. There were 30
human WNV cases reported within TRCA’s jurisdiction: 24 cases in the City of Toronto, 3 cases
in Peel Region, 2 cases in Durham Region and 1 case in York Region (Public Health Agency of
Canada 2011).
In Ontario, since the discovery of WNV in 2001, the provincial and regional health agencies have
launched various WNV monitoring and surveillance programs involving dead birds, adult
mosquitoes, larval mosquitoes and human cases. Surveillance information from birds and adult
mosquitoes is crucial for determining the immediate risk of humans contracting WNV in an area.
Larval mosquito surveillance provides important information in identifying breeding sites that
support large mosquito populations. Once the sites of concern have been identified, the regional
health units are able to take mosquito control intervention actions such as source reduction.
Source reduction, which involves eliminating favourable breeding sites and reducing mosquito
larvae through larvicide application, is an effective means of reducing the risk of WNV.
The Toronto and Region Conservation Authority (TRCA) is the largest landowner in the Toronto
region managing over 13,377 hectares of land. TRCA properties include natural and constructed
wetlands, woodland pools, reservoirs, and ponds. These aquatic ecosystems have been
considered “mosquito friendly” as a result of permanent availability of standing water (Knight et
al. 2003; Gingrich et al. 2006; Rey et al. 2006). TRCA has initiated its WNV Surveillance and
Monitoring Program since 2003 as a measure of due diligence, and also at the request of
TRCA’s regional public health partners (Regions of Peel, York, Durham and the City of Toronto).
Since the launch of the program, TRCA has been monitoring larval mosquito populations in
selected natural habitats (collectively referred to as “wetlands” in this report) and stormwater
management ponds (SWMPs). The data collected are essential to identify the sites of potential
concern or vector “hotspots” and to follow up with appropriate management actions.
There are approximately 57 mosquito species in Ontario, of which 13 species are considered
WNV vectors (Appendix 2). WNV vector mosquito species refer to the species that are capable of
carrying and transmitting the virus from one host to another. The species that do not transmit the
virus are referred to as non-vector species. Studies (Kilpatrick et al. 2005; Hamer et al. 2009)
have suggested that Culex pipiens and Culex restuans are not only the primary vectors in
spreading the disease among birds (enzootic vectors), but also the primary vectors in spreading
the disease into the human population (bridging vectors). Effectively monitoring and controlling
these two key vector species is critical for reducing WNV risk in Southern Ontario.
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
2
The results from TRCA’s WNV larval monitoring program (TRCA, 2006a; 2006b; 2007; 2008;
2010; 2011) have shown that SWMPs and healthy functioning wetlands typically do not support
high densities of mosquito populations. Occasionally, sites of concern for WNV (the numbers of
sites per year ranged from one to six between 2006 and 2011) have been identified through the
larval monitoring program. The ability to detect the sites of concern for WNV through larval
monitoring, subsequently to take appropriate control measures highlights the importance of
regular and continuous seasonal monitoring of the SWMPs and wetlands.
The TRCA WNV program focuses on reducing/eliminating WNV vector mosquito larvae and
dealing with the public concerns on TRCA properties through a three-pronged approach:
Monitoring and Surveillance: to identify sites of concern for WNV on TRCA
properties through mosquito population monitoring, and take appropriate control
measures if deemed necessary;
Public Education and Communication: to respond to public inquiries on WNV and
address standing water complaints on TRCA properties, as well as to provide WNV
information to both the public and TRCA staff; and
Collaboration with Regional Health Units: to participate in WNV advisory
committees in Peel Region, York Region, Durham Region and the City of Toronto
and to share WNV related data.
This report provides a summary of the 2011 West Nile Virus Monitoring and Surveillance
program activities.
2. Larval Mosquitoes Monitoring Methods
2.1 Larval Collection and Identification
TRCA larval mosquito monitoring and surveillance activities began on May 30th, 2011. A total of
37 wetlands and 9 SWMPs across TRCA jurisdiction (Figure 1) were routinely sampled during
the 2011 field season. The routine monitoring sites were selected based on the presence of key
vector species or a large population of any mosquito larvae in the past. The same sampling
protocol was followed as in previous years (TRCA 2004; 2006a; 2006b; 2007; 2008; 2010; 2011).
Each site was sampled four times at approximately three week intervals with a standard
mosquito dipper (diameter = 13 cm). Each site was divided into four comparatively equal
quadrants, and one sample was taken within each quadrant. Each sample consisted of 10 dips
of the mosquito dipper. Several dipping techniques including the shallow skim, complete
submersion, partial submersion, simple scoop and scraping (O’Malley, 1995) were employed to
ensure that the all types of potential mosquito habitats were sampled. Since rain drops disturb
the water surface and consequently cause mosquito larvae to disperse, no samples were
collected during a rain event.
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
3
Collected mosquito larvae were transferred to plastic vials using a dropper and enumerated per
dip for each quadrant. Larvae were then pooled by quadrant and transported to the Boyd Field
Centre in a cooler.
In addition to mosquito larvae collection, TRCA staff also collected in-situ water quality data (pH,
temperature, electrical conductivity, total dissolved solids (TDS), and dissolved oxygen (DO))
using a YSI (650 MDS) meter. Field observation data such as water clarity, type of mosquito
predators (dragonflies, damselflies, frogs, and fish) present, and vegetation type and coverage
were also recorded during site visit.
Mature mosquito (fourth instar stage) larvae collected were killed in boiling water and preserved
in 70% ethanol on the day of collection. Immature larvae collected were reared in heated
terrariums until they reached maturity before they were killed and preserved. The preserved
specimens were identified to species using mosquito taxonomic keys (Wood et al., 1979; Darsie
and Ward, 2005). Ten percent (10%) of identified mosquito specimens were randomly selected
and sent to the Peel Region Public Health Unit for identification verification as part of the Quality
Assurance and Quality Control procedure (QA/QC).
The enumerated mosquito data were entered, verified and stored in the WNV Database Version
2.7 (a Microsoft Access database) maintained on the Boyd Field Centre sever.
2.2 WNV Risk Assessment
WNV risk assessment was carried out to identify vector mosquito hotspots. Sites were ranked
based on the average number of vector larvae found per 10 dips (40 dips/4 quadrants/site)
according to the modified Wada’s method of ranking (Wada, 1956):
Sites with no vector larvae were ranked as “Nil”;
Sites with <2 vector larvae per 10 dips were ranked as “Low” density;
Sites with 2 - 30 vector larvae per 10 dips were ranked “Moderate” density; and
Sites with >31 vector larvae per 10 dips were ranked “High” density sites.
Risk ranking was applied to each vector species independently, instead of the cumulative
number of vector larvae found at each site due to species variation in biology, host preference
and the efficiency of each vector species to transmit WNV.
Only the sites with “high” density of vector larvae or vector “hotspots” were addressed. Once a
hotspot was identified through risk assessment, the respective health unit was informed and
larvicide application options were considered if warranted.
West Nile Virus Vector Monitoring and Surveillance – 2011
February 2012
4
Figure 1. Location of wetland and stormwater management pond monitoring sites, 2011.
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
5
3. Public Education and Communication
3.1 Distribution of WNV Educational Materials
In 2011, TRCA continued to increase WNV awareness, and educate the public about WNV
through:
sharing tips on personal protection against mosquito bites, reminding the public to
perform good housekeeping practices, and making the latest WNV program annual
reports available on TRCA website (http://trca.on.ca/protect/monitoring/west-nile-
virus-monitoring-program.dot);
sending internal emails to remind TRCA staff the importance of personal protection
against WNV, and providing the latest status of TRCA’s WNV monitoring program
and the status of WNV in the region and in the province; and
displaying WNV newsletters and pamphlets in TRCA offices and conservation areas
throughout the summer.
3.2 Standing Water Complaint Procedure
Complaints from the public or staff regarding standing water or mosquito activities were
addressed according to TRCA’s Standing Water Complaint Procedure (Figure 2). Once a
complaint was received, TRCA staff followed these steps:
1. Acquired background information (location, name of the complainant, contact information,
and the nature of the complaint).
2. Evaluated the location for its proximity to a routine WNV sampling station, and the sensitivity
of the area.
3. TRCA’s Finance and Business Services Division and Planning and Development Division
were consulted to review property ownership, management agreements and land regulation
information.
4. For non-TRCA property or property under management agreement, the respective regional
public unit was notified. For TRCA properties, if deemed necessary, the complaint site was
monitored following the methods described in Section 2: mosquito larval collection and
identification and WNV risk assessment.
5. When a potential hotspot was identified through risk assessment, and if larviciding was
deemed appropriate, the following agencies were notified:
respective regional public health unit
Director of the Ecology Division, TRCA – for approval to proceed with the larvicide
treatments
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
6
Receive Complaints/Enquiries:
Determine nature of Complaint
WNV / Mosquito related
enquiries
Enquiries requesting status of sensitive natural areas for
larviciding permit
Refer caller to MNR Aurora District (John
Pisapio)
TRCA Property?
Determine property ownership, verify land regulations with Planning & Development
Division
NO YES
Property under Management Agreement
Property Managed by TRCA
Notify Health Units of Ownership and
Regulations
Refer to Health Unit and land Managers and notify
if regulated1
Review site, Collect samples, risk rank site
Notify Health Units of results
Determine control options and carry out treatment
Verify land regulations
Notify caller
The Ministry of the Environment (MOE)– to obtain the permit for larviciding
The Ministry of Natural Resources (MNR)– to review the sensitivity of the area
Finance and Business Services Division, TRCA – to obtain a private pesticide contractor
6. Notified the complainant the results of the investigation.
Figure 2. TRCA Standing Water Complaint Procedure
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
7
4. Collaboration with Regional Health Units TRCA has been working closely with its regional public health unit partners since the launch of
the WNV monitoring program. The collaboration efforts involved notification of vector hotspots,
and participation in advisory committees. In addition, TRCA also provided mosquito larval
identification training to staff from the Durham Regional Health Unit in May, 2011. The
participants learned to identify WNV vector and non-vector mosquito larvae typically found in
Southern Ontario.
TRCA was also ordered to assist with the implementation of control measures to reduce the
number of mosquito larvae in the Heart Lake Wetland Complex in Brampton. The Order was
issued on April 7, 2011 by the Medical Officer of Peel Regional under the Health Protection and
Promotion Act, R.S.O. 1990, c. H.7.
Based on sampling activities conducted by Peel Public Health Unit, three locations within the
Heart Lake Wetland Complex were successfully treated from July to September, 2011 (Paul
Proctor, Peel Region, Vector-Borne Disease Team Supervisor, pers. comm.). These locations
were treated with Bacillus thuringiensis israelensis, commonly referred to as Bti. Bti is a
bacterium found naturally in soils, and since 1982, it has been used successfully worldwide as a
biological pest control agent to combat mosquitoes and black flies (Health Canada 2011).
5. Results and Discussion
5.1 Mosquito Larval Density
In total, 8233 mosquito larvae were collected from the routine monitoring sites during the 2011
field season, including 6784 mosquito larvae collected from 37 wetlands and 1449 mosquito
larvae collected from 9 SWMPs. A total of 13 mosquito species were collected across all sites in
2011 including 5 non-vector species (Anopheles earlei, Culex territans, Culiseta inornata,
Psorophora ferox, and Uranotaenia sapphirina) and 8 WNV vector species (Aedes vexans,
Anopheles punctipennis, Anopheles quadrimaculatus, Culex pipiens, Culex restuans, Culex
salinarius, Ochlerotatus japonicus, and Ochlerotatus trivittatus). The most abundant species in
terms of distribution was Culex territans which inhabited 39 of the 46 (85%) sampled sites. The
two key vectors, Culex pipiens and Culex restuans, were found in 37% (n=17) and 22% (n=10)
of the sampled sites respectively.
The incidence of larval mortality during the rearing process dropped from 32% (the 5-year
average from 2006 to 2010) to 10% in 2011; this rearing mortality reduction was achieved by
separating mosquito larvae by maturity (size) and genera, and by rearing fewer larvae in each
rearing container.
The overall summary of the results from the 2011 WNV monitoring season is presented in
Appendix C.
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
8
5.1.1 Wetlands
TRCA collected 6784 mosquito larvae among the 37 selected wetlands. Some collected
mosquito larvae (n=761) had died prematurely or had gone missing during the rearing process.
These larvae were unable to be indentified, thus they were not included in the statistical analysis
provide later in this report. The identified larvae (n=6023) consisted of 2775 (46.1%) vector
mosquito species larvae and 3248 (53.9%) non-vector mosquito species larvae. The vector
species to non-vector species ratio fluctuated from year to year (Figure 3) in wetlands,
depending on many complex biotic and environmental factors. At Grenadier Pond in High Park,
a significantly large number of Culex pipiens were collected on August 2, 2011 (n=1336, which
represented nearly half of the vector mosquito larvae collected among all wetlands in the
season). If the site at Grenadier Pond was removed from the data set, 71.5% of the larvae
collected were non-vector species, while the remaining 28.5% were vectors among the other
wetlands.
Figure 3. Vector and non-vector mosquito larvae composition in wetlands from
2006 – 2011.
In total, 13 species (8 vector species and 5 non-vector species) of mosquito larvae were found in
the sampled wetlands. The predominant non-vector species was Culex territans (52.7%),
followed by Uranotaenia sapphirina (1.0%), Anopheles earlei (<0.1%), Culiseta inornata (<0.1%),
and Psorophora ferox (<0.1%) (Figure 4). The predominant vector species was Culex pipiens
(31.2%), followed by Anopheles quadrimaculatus (4.7%), Anopheles punctipennis (4.0%), Aedes
vexans (3.1%), Culex restuans (2.6%), Culex salinarius (0.5%), Ochlerotatus trivittatus (<0.1%)
and Ochlerotatus japonicus (<0.1%) (Figure 4).
61.5% 29.0%26.5%
64.4%
46.1%38.5%
81.9%
71.0%
73.5%
35.6% 53.9%
0
1000
2000
3000
4000
5000
6000
7000
2006 2007 2008 2009 2010 2011
No
. o
f m
osq
uit
o larv
ae
Sampling year
non-vectors vectors
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
9
Figure 4. Mosquito species composition in wetlands, 2011.
The summer of 2011 was dry; the total precipitation over the summer (June to August) was 189
mm, compared to 351 mm in 2010, 309 mm in 2009, and 341 mm in 2008. This unusually dry
weather resulted in a number of sites being either completely or partially dried up by the second
and subsequent sampling events. Refer to Appendix D for the locations of sites that dried up
during the sampling season.
Due to the dry and warm summer conditions in 2011, many of the routine monitoring sites turned
into shallow, warm and stagnant pools of water. Water temperature rises much faster in shallow
pools of water. Studies (Cranston et al. 1987; Bradford 2005) have shown that rising
temperatures promote larval development, and weather conditions directly impacts the
abundance of Culex pipiens, which increases its hatching rate from 3 days at 20 oC to 24 hours
at 30 oC. This might contribute to the increased numbers of Culex pipiens collected in the
sampled wetlands this year (Figure 4).
Aedes vexans, representing 34% (n=1875) of larvae collected from wetlands was the
predominant species in 2010. However, in 2011, much smaller numbers of this species were
found (n=190; 3.1%). The preferred larval habitats for this species are open, shallow grass-filled
depressions in pastures, roadside ditches and temporary woodland pools that have the
tendency to get periodic flooding (Wood et al. 1979). Consequently, the distribution and
abundance of Aedes vexans depends upon rainfall patterns as they depend upon rain to restore
Culex territans53.1%
Uranotaenia sapphirina
1.0%
Culex pipiens 31.4%
Anopheles quadrimaculatus
4.7%
Anopheles punctipennis
4.0%
Aedes vexans3.1%Culex restuans
2.6%
Vector species45.9%
Cx. salinarius, Oc. trivittatus, Oc. japonicus, An. earlei, Cs. inornata, and Ps. ferox accounted for less than 1% of mosquito larvae combined, therefore, these species were not included in the figure.
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
10
their breeding habitat. The unusually dry summer in 2011 might have contributed to the dramatic
reduction in Aedes vexans population.
Uranotaenia sapphirina has been found from south-eastern Canada to Florida along the eastern
seaboard of the United States. Its range extends into the central states west to North Dakota
and south into Mexico. It has been considered rare in southern Ontario (Wood et al. 1979).
TRCA collected 62 individuals (1% of all larvae collected, Figure 4) in 8 different wetlands in
2011; this finding might suggest that this species could be expanding its distribution
northwards.
5.1.2 Stormwater Management Ponds
A total of 1447 mosquito larvae were collected among the 9 SWMP monitoring sites. Mosquito
larvae (n=70) that had died prematurely or had gone missing during the rearing process could
not be identified and consequently, were not included in the statistical analysis provide later in
this report. The identified larvae (n=1379) consisted of 1151 (83.5%) vector mosquito species
larvae and 228 (16.5%) non-vector mosquito species larvae. The ratio of vector species to non-
vector species observed indicated that the mosquitoes collected from SWMPs were
predominantly vector species; the composition was similar to previous years (Figure 5).
Figure 5. Vector and non-vector mosquito composition in stormwater
management ponds, 2006 – 2011.
96.0%
99.0%
68.2%
86.2% 88.7%
83.5%4.0%
1.0%
31.8%
13.8%11.3%
16.5%
0
500
1000
1500
2000
2500
2006 2007 2008 2009 2010 2011
No
. o
f m
osq
uit
o larv
ae
Sampling year
Non-vector Vector
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
11
During the 2011 sampling period, the following five vector mosquito species were collected in
order of abundance: Culex pipiens (73.7%), Culex restuans (3.8%), Anopheles Punctipennis
(3.8%), Anopheles quadrimaculatus (1.9%), Aedes vexans (0.4%), and Culex salinarius (0.1%)
(Figure 6). Similar to previous years, Culex territans was the only non-vector species collected,
representing 16.5% of the mosquito larvae found in the SWMPs.
Figure 6. Mosquito species composition in stormwater management ponds,
2011.
Compared to the wetlands, the number of species collected and their overall abundance was
lower in the SWMPs. The differences could be attributed to several facts:
Habitat preference of certain species – Species such as Culiseta inornata and
Psorophora ferox prefer temporary, rain-filled pools, particularly in or near wooded areas,
in overflow pools along streams and occasionally in potholes in stream beds after
summer rains (Wood et al. 1979). These species were absent from the sampled SWMPs.
High exposure to wind and frequent runoffs into SWMPs might cause recurrent and
continuous disturbance to habitats that mosquitoes need for depositing their eggs and
breathing. The summers of 2007 and 2011 were drier than usual and our data have
shown that there is a correlation between the lack of precipitation (fewer disturbances)
and the higher number of mosquito larvae collected in the SWMPs (Figure 5).
Culex territans16.5% Aedes
vexans0.4%
Culex pipiens 73.7%
Anopheles quadrimaculatus
1.9%
Anopheles punctipennis
3.8%
Culex restuans3.8%
Vector Species83.5%
Culex salinarius was represented by only one individual, and was therefore not included in the figure.
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
12
Regional health units continue to monitor SWMPs and apply larvicide periodically.
5.1.3 Interspecies competition between key vector species
The two key WNV vector species Culex pipiens and Culex resturans are ecologically similar
species and prefer similar breeding sites (Reiskind et al., 2008). Culex pipiens, an introduced
species, and Culex resturans, a native species, appear to coexist in the sampled sites. In 2011,
the abundance of Culex pipiens increased, while the abundance of Culex restuans decreased
slightly. These results might suggest that the introduced Culex pipiens is out-competing the
native Culex restuans in both wetland habitats and SWMPs. More data are necessary to
understand the complex interspecies relationship between Culex pipiens and Culex resturans.
All other interspecies associations were statistically non-significant.
5.2 Risk Assessment and WNV Vector Hotspot Identification
In total, 167 samples (46 sites x 4 sampling events – sites that dried up completely) were taken
from the monitoring sites in 2011, and only 6 samples were determined to have high densities of
WNV vector species. Mosquito control measures were taken to deal with WNV vector hotpots
after they were determined through risk assessment.
5.2.1 Wetlands
Risk assessment was performed on vector species found at each wetland site to determine WNV
risk. Most routinely monitored wetlands were determined to pose “nil”, “low” or “moderate” risk.
Only three wetland sites were identified as WNV vector hotspots in 2011 (Table 1, Appendix D).
Table 1. List of WNV vector hotspots in wetlands, 2011.
Site Region No. of vector larvae/
10 dips
Vector
species
Sampling
date
High Park – Grenadier
Pond
Toronto 334 Culex pipiens August 2
Altona Forest – Lacey’s
Pond
Durham 41 Culex pipiens August 16
TTP – Goldfish Pond Toronto 56 Culex pipiens August 23
The City of Toronto applied larvicide treatments at Grenadier Pond in High Park upon
notification. The treatments were effective. When the pond was sampled again on August 31, the
number of Culex pipiens larvae reduced from 334 to 7 per 10 dips. Lacey’s Pond in Altona Forest
was treated by TRCA’s pesticide contractor (GreenLeaf Pest Control), after a permit was
obtained from the MOE, and the Altona Forest Stewardship Committee was informed. Goldfish
Pond in Tommy Thompson Park was not treated due to the sensitivity of the area (presence of
species at risk) and the late seasonal timing of the discovery of the hotspot.
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
13
5.2.2 Stormwater Management Ponds
A risk assessment was performed on vector species found in each SWMP to determine WNV
risk. Most routinely monitored SWMPs were determined to pose “nil”, “low” or “moderate” risk.
Only two SWMPs were identified as WNV vector hotspots (Table 2, Appendix E).
Table 2. List of WNV vector hotspots in stormwater management ponds, 2011.
Site Region No. of larvae/
10 dips
Vector species Sampling date
SWMP 279.1 Durham 50 Culex pipiens July 22
L’Amoreaux Park North Pond Toronto 105 Culex pipiens July 22
L’Amoreaux Park North Pond Toronto 30 Culex pipiens August 18
Similar to previous years, large numbers of Culex pipiens were found in L’Amoreaux Park North
Pond. This pond is under Management Agreement with the City of Toronto and the monitoring
results were forwarded to the public health staff. This site was subsequently larvicided by the
City of Toronto. The pond was sampled again on August 18, 2011, and it was once again
identified as a hotspot; after communicating with the public health staff, it was understood that
the treatment of this pond was on-going.
SWMP 279.1 was identified as a hotspot in late July, 2011. When the Durham Public Health Unit
was notified, TRCA was informed that all SWMPs in Durham Region were already being
monitored and treated if necessary. After a brief meeting with Durham Public Health staff, it was
established that TRCA will suspend the monitoring of all three SWMPs in Durham in 2012. All of
the monitored SWMPs are under management agreements; to avoid duplication in SWMPs
monitoring, a detailed list of TRCA’s monitoring sites will be distributed to all our regional public
health partners before monitoring season starts in 2012.
5.2.3 Standing Water Complaint Sites
In 2011, TRCA received seven standing water complaints associated with TRCA properties. Two
of these properties (YORK04 and YORK05) had been added onto the routine monitoring list
since 2010. Both of these sites dried up completely after the first sampling event (on June 14th,
2011), therefore very few mosquito larvae were collected at these two sites. One property,
Guildwood Park, is under a management agreement with the City of Toronto; therefore, the
information was provided to City staff. The other four properties were investigated and sampled
on a weekly basis following the sampling methods described in Section 2. Three sites were
located in York Region and one site was located in Durham Region. Site YORK02 was identified
as a moderate risk site in July, however the area dried up completely when visited a week later
and remained dry for the rest of the season. The rest of the complaint sites were monitored until
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
14
the end of the season. They were identified as low risk sites (Table 3), and no larvicide
treatments were warranted.
Additionally, TRCA also received three complaints associated with either public land or private
property; these non-TRCA property complaints were forwarded to the respective regional public
health units.
Table 3. Results of standing water complaint investigation, 2011.
Site Sampling
Date
Species Total
count
# of vector/
10 dips
Risk ranking
DURHAM01 29-Aug-11 Cx. territans 11 Non-vector
An. punctipennis 2 <1 LOW
An. quadrimaculatus 4 1 LOW
06-Sep-11 Cx. territans 25 Non-vector
An. punctipennis 6 1-2 LOW
An. quadrimaculatus 2 <1 LOW
YORK01 12-Jul-11 An. quadrimaculatus 10 2-3 MODERATE
An. punctipennis 1 <1 LOW
YORK02 11-Aug-11 Cx. territans 64
Non-vector Ur. sapphirina 1
An. walkeri 1
An. punctipennis 1 <1 LOW
An. quadrimaculatus 5 1-2 LOW
Cx. pipiens 2 <1 LOW
19-Aug-11 Cx. territans 52 Non-vector
Ur. sapphirina 5
An. quadrimaculatus 8 2 LOW
25-Aug-11 Cx. territans 21 Non-vector
An. quadrimaculatus 2 <1 LOW
06-Sep-11 Cx. territans 15 Non-vector
Ur. sapphirina 2
An. punctipennis 3 <1 LOW
An. quadrimaculatus 5 1-2 LOW
Cx. pipiens 3 <1 LOW
YORK03 25-Aug-11 Cx. territans 29 Non-vector
An. punctipennis 8 2 LOW
An. quadrimaculatus 8 2 LOW
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
15
5.3 Mosquito species composition and in-situ water quality
In 2011, TRCA continued to investigate the potential correlation between larval mosquito species
composition and water quality (pH, temperature, electrical conductivity, total dissolved solids,
and dissolved oxygen) and site characteristics. However similar to previous years, the data
collected in 2011 showed no statistically significant correlation between mosquito species
composition and water quality. In-situ water quality data were collected at one of the four
sampled quadrants at each site in previous years. In 2012, all in-situ data will be collected at all
four quadrants of each site. More data points might facilitate the discovery of any potential
correlation between mosquito species composition and site characteristics.
6. Conclusions and Recommendations
The number of mosquito larvae collected (n=8233) during the 2011 WNV season was the
second highest since the start of the TRCA WNv surveillance program (the highest being the
year 2010 with 9389 larvae) despite a number of sites drying up either partially or completely.
The improved rearing techniques reduced the rearing mortality rate from 32% (the 5-year
average from 2006 to 2010) to 10%.
The data from 2011 supported the findings from the previous TRCA studies. The studies showed
that wetlands do not generally support high densities of WNV vector larvae, and larval
monitoring in the SWMPs yielded lower numbers of mosquito larvae overall, but the majority of
the larvae were WNV vectors. The data also suggested that wetland habitats support a more
diverse mosquito population with greater abundance, and Culex pipiens and Culex resturans
have a preference for SWMPs over wetlands. The unusually dry and hot summer seemingly
created an ideal condition for Culex Pipiens to breed; this may have contributed to the increased
reported human cases in Ontario. The detection of isolated hotspots like SWMP 279.1,
L’Amoreaux Park North Pond, Grenadier Ponds, Lacey’s Pond, and Goldfish Pond signified the
importance of continuous larval mosquito monitoring across TRCA jurisdiction.
TRCA received and addressed seven standing water complaints associated with TRCA
properties as per TRCA’s Standing Water Complaints Procedure. No complaint sites were
deemed hotspots in 2011, however two complaint sites (YORK01 and DURHAM01) could
potentially be sites of concern in the future and additional monitoring effort should be invested in
monitoring and investigating these sites in 2012.
Collaboration with MNR, MOE, local stewardship committees, and TRCA’s management team is
crucial in terms of managing WNV vector hotpots in a timely manner on TRCA properties. A
TRCA WNV Monitoring and Surveillance Program work plan for the 2012 WNV season will be
developed before the field season starts. Once the locations of the routine monitoring sites have
been finalized, the management biologist at MNR will be informed of all the sampling sites, a full-
season permit from the MOE to larvicide high WNV risk sites will be requested, and the local
stewardship committee and the manager responsible for each of the monitoring sites will also be
informed of the WNV activities in the coming year.
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
16
A predictive statistical model has been developed by the Laboratory of Mathematical Parallel
Systems (LAMPS) at York University; the model uses weather data to predict WNV vector
abundance with reasonable accuracy. The researchers at York University are optimistic
regarding the development of weather-generated forecasting for WNV risk that could be used in
decision support systems for interventions such as mosquito control in Ontario.
According to Dr. Robbin Lindsay, Chief, Field Studies, Public Health Agency of Canada, (Ministry
of Health and Long Term Care 2009) the long-term strategies for WNV management will be that:
―Localized ―hotspots‖ for WNV virus amplification and risk of human disease will likely be
maintained within some/many jurisdictions. The disease burden will vary within jurisdictions from
year to year, driven by abiotic and biotic factors….., managing WNV means to maintain regional
appropriate surveillance and capacity to intervene—at least in areas of greatest risk, …., to
commit to two planks of WNV prevention (personal protective measures (PPM) and Integrated
Mosquito Management (IMM) and vital to all this is the sustainability of programs‖.
West Nile Virus Vector Monitoring and Surveillance – 2011 February 2012
17
7. References
Bradford C.M., 2005. Effects of weather on mosquito biology, behavior, and potential for West
Nile Virus transmission on the southern high plains of Texas, a dissertation in
experimental toxicology. Doctoral dissertation Texas Tech University, 2005. 24 pages.
Cranston, P.S., Ramsdale, C.D., Snow, K.R. & White, G.B., 1987. Adults, larvae and pupae of
British mosquitoes (Culicidae). Freshwater Biological Association, Ambleside, Cumbria.
Scientific Publication, no. 48, pp. 1–152
Darsie, R.F and R.A. Ward, 2005. Identification and Geographical Distribution of the Mosquitoes
of North America, North of Mexico. University Press of Florida, Gainesville, Florida, 383
Pages.
Gingrich, J.B., D. Robert, G.M. Williams, L. O’Connor and K. Harkins, 2006. SWMPs,
constructed wetlands, and other best management practices as potential breeding sites
for West Nile Virus vectors in Delaware during 2004. J. Amer. Mos. Con. Asso., Vol. 22
(2): 282 -291.
Hamer GL, Kitron UD, Goldberg TL, Brawn JD, Loss SR (2009) Host selection by Culex pipiens
mosquitoes and West Nile Virus amplification. Am J Trop Med Hyg 80: 268–278.
Health Canada. 2011. Bti – Bacillus thuringiensis subspecies israelensis.
http://www.hc-sc.gc.ca/cps-spc/alt_formats/pdf/pubs/pest/_fact-fiche/bti-eng.pdf
Kilpatrick, A.M., L.D. Kramer, S. Campbell, E.O. Alleyne, A.P. Dobson, P. Daszak. 2005. West
Nile Virus Risk Assessment and the Bridge Vector Paradigm. Emerging Infectious
Diseases., Vol. 11(3) 425-429.
Knight, R. L., W. E. Walton, G. F. O’Meara, W. K. Reisen and R. Wass. 2003. Strategies for
effective mosquito control on constructed treatment wetlands. Ecol. Eng., Vol 21: 211-
232. Ministry of Health and Long-term Care, 2009. West Nile Virus Preparedness and Prevention
Plan - 2009. 53 Pages.
http://www.health.gov.on.ca/english/public/pub/ministry_reports/wnv_plan_2009/wnv_pl
an_full.pdf
O’Malley, C. 1995. Seven ways to a successful dipping career. Wing Beats. 6:23-24.
Public Health Agency of Canada, 2011. West Nile Virus MONITOR. Weekly Up Dates: Human
and Dead Bird Surveillance. http://www.phac-aspc.gc.ca/WNV-vwn/index.html.
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Reiskind, M. H. and M. L. Wilson, 2008. Interspecific competition between larval Culex restuans
Theobald and Culex pipiens L. (Diptera: Culicidae) in Michigan. Journal of Medical
Entomology 45(1): 20-27.
Rey, J. R., G. O’Meara, S. M. O’Connell and M. M. Cutwa-Francis, 2006. Mosquito production
from four constructed treatment wetlands in peninsular Florida. J. Amer. Mos. Con.
Asso., Vol. 22 (2): 198 - 205.
Toronto and Region Conservation Authority, 2004. Report on West Nile Virus in Conservation
Wetlands. March 2004.
Toronto and Region Conservation Authority, 2006a: Report on West Nile Virus in Toronto and
Region Conservation Wetlands and Stormwater management ponds 2004 -2005. 85
Pages.
Toronto and Region Conservation Authority, 2006b. Annual Report: West Nile Virus Vector
Status in Toronto and Region Conservation Wetlands and Stormwater management
ponds– 2006. 12 Pages.
Toronto and Region Conservation Authority, 2007. Annual Report: West Nile Virus Vector Status
in Toronto and Region Conservation Wetlands and Stormwater management ponds–
2007. 24 Pages.
Toronto and Region Conservation Authority, 2008. Annual Report: West Nile Virus Vector
Mosquito Larval Surveillance and Monitoring - 2008. 42 Pages.
Toronto and Region Conservation Authority, 2010. Annual Report: West Nile Virus Vector
Mosquito Larval Surveillance and Monitoring – 2009. 31 Pages.
Toronto and Region Conservation Authority, 2011. Annual Report: West Nile Virus Vector
Mosquito Larval Surveillance and Monitoring – 2010. 26 Pages.
Wada, Y., 1956. Population Studies on Edmonton Mosquitoes. Questions ent. Vol.1: 187- 222.
Wood, D.M., P.T. Dang and R. A. Ellis, 1979. The Insects and Arachnids of Canada. Part 6: The
Mosquitoes of Canada Diptera: Culicidae. Publication 1686, Agriculture Canada, 361
Pages.
Appendices
Appendix A. Total Reported West Nile Virus Clinical Cases in Canada: 2002-2011.
This table was adapted from Public Health Agency of Canada website. <http://www.phac-aspc.gc.ca/wnv-vwn/mon-hmnsurv-archive-eng.php#a2002_07>
Province/Territory 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
Newfoundland and Labrador 0 0 0 0 0 0 0 0 0 0
Prince Edward Island 0 0 0 1 0 0 0 0 0 0
Nova Scotia 0 2 0 1 0 1 0 0 0 0
New Brunswick 0 1 0 1 0 0 0 0 0 0
Quebec 20 17 3 4 1 2 2 1 0 37
Ontario 394 89 13 95 42 12 3 4 1 64
Manitoba 0 142 3 55 50 578 12 2 0 0
Saskatchewan 0 937 5 58 19 1285 17 1 2 0
Alberta 0 272 1 10 39 318 1 2 1 0
British Columbia 0 20 0 0 0 19 1 3 1 0
Yukon 0 1 0 0 0 0 0 0 0 0
Northwest Territories 0 0 0 0 0 0 0 0 0 0
Nunavut 0 0 0 0 0 0 0 0 0 0
Total 414 1481 25 225 151 2215 36 13 5 101
Appendix B. WNV vector species of concern in Ontario (Ministry of Health and
Long Term Care, 2009).
*The highlighted species were found within TRCA jurisdiction in 2011.
Species Name
Culex pipiens
Culex restuans
Culex salinarius
Culex tarsalis
Aedes vexans
Anopheles punctipennis
Anopheles quadrimaculatus
Anopheles walkeri
Ochlerotatus canadensis
Ochlerotatus japonicus
Ochlerotatus stimulans
Ochlerotatus triseriatus
Ochlerotatus trivittatus
Appendix C. Overall summary the 2011 WNV monitoring season results.
Species Wetlands SWMPs
Vector Species Density Abundance (# of sites)
Density Abundance (# of sites)
Culex pipiens 1878 10 1015 7
Culex restuans 157 4 52 6
Culex salinarius 27 6 1 1
Aedes vexans 185 7 5 2
Anopheles punctipennis
241 21 52 5
Anopheles quadrimaculatus
284 23 26 5
Ochlerotatus japonicus
1 1 - -
Ochlerotatus trivittatus
3 2 - -
Non-Vector Species
Density Abundance (# of sites)
Density Abundance (# of sites)
Culex territans 3175 32 228 7
Anopheles earlei 5 4 - -
Culiseta inornata 4 3 - -
Psorophora ferox 1 1 - -
Uranotaenia sapphirina
62 8 - -
Missing/rearing mortality
761 70
Total 6784 1449
Appendix D. Risk ranking for WNV of wetland sites for 2011.
Sites were ranked based on the average number of vector larvae found per 10 dips (40 dips/4 replication)
according to the modified Wada’s method of ranking (Wada, 1956): with no vector larvae = “Nil”(_), with <2 vector larvae per 10 dips = “Low” ( L ), with 2 L 30 vector larvae per 10 dips = “Moderate” (M); and with
>31 vector larvae per 10 dips = “High” (H). (x) indicates the site was completely dry during a sampling event
Region
Site
West Nile Virus Vector Species
Cx. pipiens Cx. restuans An.
quadrimaculatus An. punctipennis Ae. vaxans
Sampling Interval 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Durham Region
Altona Forest Conservation Area
Altona Forest H L L M M M
Claremont Conservation Area
Wetland 1 L L M M L L
Wetland 2 L L M M L L
Carruther’s Creek
Swamp Complex x x x x x x x x x x
Frenchman’s Bay
Frenchman’s Bay Promenade
L L L L
GreenWood Conservation Area
Greenwood Marsh L L L
Greenwood Pond x M x x L x L x L
Peel Region
Albion Hills Conservation Area
Pond 1
Pond 2 x x x x x x x x x x x x x x x
Pond 4 L L L M M
Clairville Conservation Area
Wetland 1 x x x x x x L x x x x
Wetland 2 x x x x L L x x L L x x x x
Heart Lake Conservation Area
Heart Lake New Site
L L
Glen Haffy Conservation Area
Trout Pond 1 L M M M M M M
Trout Pond 2 L L L M M
Marie Curtis Park
Marie Curtis Wetland 1
L L
Appendix D. (Continued)
Region Site
West Nile Virus Vector Species
Cx. pipiens Cx. restuans An.
quadrimaculatus An.
punctipennis Ae. vaxans
Sampling Interval
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Toronto Col. Samuel Smith Park
Mini Pond
Main Pond L L
Eglington Flats
Topham Pond L M M
Woodland Pond M L M L L
High Park
Grenadier Pond L M H M M M M L L L
Humber Bay Boat Park
Mimico Amphibian Pond
Milne Hollow
Milne Pond
Tommy Thompson Park
Triangle Pond
Goldfish Pond H M
York Region
Bruce’s Mill Conservation Area
Bruce’s Mill L M M L L
Boyd Field Centre
YORK04 x x x M x x x x x x x x x M x x x
Granger Wetland (South Pond)
L M M L L
Boyd Wetland M M L L L L L M
Cold Creek Conservation Area
Wetland L L
Pond L L L L L
North Maple
YORK05 x x x x x x x x x x x x x x x
German Mills Creek
Elgin Mills Rd. x M x x L L x L x M M
Keffer Marsh
Keffer Marsh L L L L L L
Kortright Conservation Area
Kortright Marsh L L L L L L
Stouffville Conservation Area
Stouffville Reservoir
L
Toogood Pond Park
Toogood Pond
Appendix E. Risk ranking of stormwater management pond sites for 2011.
Sites were ranked based on the average number of vector larvae found per 10 dips (40 dips/4 replication) according to the modified Wada’s method of ranking (Wada, 1956): with no vector larvae = “Nil”(_), with <2 vector larvae per 10 dips = “Low” ( L ), with 2 L 30 vector larvae per 10 dips = “Moderate” (M); and with >31 vector larvae per 10 dips = “High” (H). (x) indicates the site was completely dry during a sampling event.
Region
SWMPs
West Nile Virus Vector Species
Cx. pipiens Cx. restuans An.
quadrimaculatus An.
punctipennis Ae. vaxans
Sampling Interval 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Durham Region
253 L L L L L L L
262 M M M L
279.1 M H L L L L L L M M
Peel Region
174 L M L
Toronto L’Amoreaux Park North M H H L L M L L
L’Amoreaux Park South L L L L L
York Region
88.2 M M L L L L L L
139 L L
Killian Lamar L
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