Mosquito surveillance data reports the abundance of various
species of mosquitoes in San Mateo County.
Different mosquito species have different seasonal life cycles,
bite different hosts at different times of day, and transmit
different diseases. It’s important for District staff to know
what mosquito species are present in order to minimize annoyance
and, more importantly, disease risk to humans and domestic
animals.
These graphs track the number of mosquitoes of each species
(vertical axis) by month (horizontal axis). These are frequently
compared to a five-year average of each mosquito species by
month, allowing staff to determine whether we have more, less, or
about the same mosquito populations as most years.
For more information about how the District traps mosquitoes for
disease and population surveillance, see Mosquito Trapping and Pools.
The following table and graph show the average number of
mosquitoes collected per CO2 trap per night during the
month of December compared to the five-year average for the six
most common mosquito species in San Mateo County. Counts for all
species continue to decline as we progress into the cooler
season. Culex pipiens, the northern house mosquito, was
the most abundant mosquito collected this month and was collected
in above average numbers. This species breeds in catch basins,
water under buildings, and residential containers in yards.
This December, 68 larval samples were collected in the field by
vector control technicians and identified by the lab. The most
frequently occurring species in larval samples was Aedes
washinoi, the woodland pond mosquito, found in 26 of the 68
samples. This seasonal mosquito species breeds in
shallow ground pools filled by winter rains and overflows from
rivers and streams. Culiseta incidens, the cool
weather mosquito, was the second most frequent species found,
present in 23 of the 68 samples. Both Cs.
The following table and graph show the average number of
mosquitoes collected per CO2 trap per night during the
month of November compared to the five-year average for the six
most common mosquito species in San Mateo County. Counts for all
species continue to decline as we progress into the cooler
season. Culex pipiens, the northern house mosquito, was
the most abundant mosquito collected this month and was collected
in above average numbers. This species breeds in catch basins,
water under buildings, and residential containers in yards.
This November, 50 larval samples were collected in the field by
vector control technicians and submitted to the lab. The most
frequently occurring species in larval samples was Culiseta
incidens, the cool weather mosquito, present in 38 of the 50
samples. This mosquito is present year-round in San Mateo County
and frequently collected from fish ponds, containers holding
water, and fresh water impounds. Culex pipiens, the
northern house mosquito, was also collected frequently this past
month. Culex pipiens is the most common mosquito in San
Mateo County.
The following table and graph show the average number of
mosquitoes collected per CO2 trap per night during the
month of October compared to the five-year average for the six
most common mosquito species in San Mateo County. Culex
pipiens, the northern house mosquito, was the most abundant
mosquito collected this month and was collected in above average
numbers. This species breeds in catch basins, water under
buildings, and residential containers in yards.
During October, larval surveillance focused on back yard sources
like fountains, ponds, and containers in addition to catch
basins. A technician uses a dipper to take a sample of the water
and visually inspects it for mosquito larvae. If larvae are
present, the technician transports the sample to the laboratory
for counts and identification. This October, 108 larval samples
were submitted to the lab. The most frequently occurring species
in larval samples was Culiseta incidens, the cool
weather mosquito, present in 81 of the 108 samples.
The following table and graph show the average number of
mosquitoes collected per CO2 trap per night during the month of
September compared to the five-year average for the six most
common mosquito species in San Mateo County. Culex pipiens, the
northern house mosquito, was the most abundant mosquito collected
this month and was collected in above average numbers. This
species breeds in catch basins, water under buildings, and
residential containers in yards. A considerable number of Culex
erythrothorax were collected in traps during September,
especially from Mills Field in San Bruno.
During September, larval surveillance focused on back yard
sources like fountains, ponds, and containers in addition to
catch basins. A technician uses a dipper to take a sample of the
water and visually inspects it for mosquito larvae. If larvae are
present, the technician transports the sample to the laboratory
for counts and identification. This September, 72 larval samples
were submitted to the laboratory. The most frequently occurring
species in larval samples was Culiseta incidens, the
cool weather mosquito, present in 51 of the 72 samples.
The following table and graph show the average number of
mosquitoes collected per CO2 trap per night during the
month of August compared to the five-year average for the six
most common mosquito species in San Mateo County. Culex
pipiens, the northern house mosquito, was the most abundant
mosquito collected this month and was collected in above average
numbers. This species breeds in catch basins, water under
buildings, and residential containers in yards. A considerable
number of Cx.
During August, larval surveillance focused on back yard sources
like fountains, ponds, and containers in addition to catch
basins. A technician uses a dipper to take a sample of the water
and visually inspects it for mosquito larvae. If larvae are
present, the technician transports the sample to the laboratory
for counts and identification. This August, 49 larval samples
were submitted to the laboratory. The most frequently occurring
species in larval samples was Culiseta incidens, the cool weather
mosquito, present in 40 of the 49 samples.
The following table and graph show the average number of
mosquitoes collected per CO2 trap per night during the
month of July compared to the five-year average for the six most
common mosquito species in San Mateo County. Culex
erythrothorax, the tule mosquito, was the most abundant
mosquito collected this month and was collected in above average
numbers. This species breeds among tule plants (cattails) in
fresh water. Most of the Cx. erythrothorax mosquitoes
collected in July came from Mills Field in San Bruno.
During July, larval surveillance focused on back yard sources
like fountains, ponds, and containers in addition to catch
basins. A technician uses a dipper to take a sample of the water
and visually inspects it for mosquito larvae. If larvae are
present, the technician transports the sample to the laboratory
for counts and identification. This July, 43 larval samples were
submitted to the laboratory. The most frequently occurring
species in larval samples was Culiseta incidens, the
cool weather mosquito, present in 29 of the 43 samples.
The following table and graph show the average number of
mosquitoes collected per CO2 trap per night during the
month of June compared to the five-year average for the six most
common mosquito species in San Mateo County. Culex
pipiens, the northern house mosquito, was the most abundant
mosquito collected this month and was collected in above average
numbers. This species breeds in urban and suburban sources,
especially in warm weather. A considerable amount of Cx.
During June, larval surveillance focused on back yard sources
like fountains, ponds, and containers in addition to catch
basins. A technician uses a dipper to take a sample of the water
and visually inspects it for mosquito larvae. If larvae are
present, the technician transports the sample to the laboratory
for counts and identification. This June, 79 larval samples were
submitted to the laboratory. The most frequently occurring
species in larval samples was Culiseta incidens, the
cool weather mosquito, present in 50 of the 79 samples.
The following table and graph show the average number of
mosquitoes collected per CO2 trap per night during the
month of May compared to the five-year average for the six most
common mosquito species in San Mateo County. Aedes
washinoi, the fresh water mosquito, was the most abundant
mosquito collected this month. This species breeds in fresh water
impounds and marshes. It emerged in high numbers this spring,
especially from sources in Mills Field, near San Francisco
International Airport. These mosquito sources are now under
control.
During May, larval surveillance continued in remaining marshes
and seasonal impounds while technicians also increased
inspections of back yard and underground sources that can create
mosquito problems throughout the summer. A technician uses a
dipper to take a sample of the water and visually inspects it for
mosquito larvae. If larvae are present, the technician transports
the sample to the laboratory for counts and identification. This
May, 97 larval samples were submitted to the laboratory.
The following table and graph show the average number of
mosquitoes collected per CO2 trap per night during the
month of April compared to the five-year average for the six most
common mosquito species in San Mateo County. Adult mosquito
abundances rose in April, which is typical. Aedes
sierrensis, the western tree-hole mosquito, was the most
abundant mosquito collected this month. This species breeds in
tree-holes that hold seasonal water, which are numerous because
of the higher than average rainfall this winter.
Surveillance for mosquito larvae in seasonal impounds and marsh
sources continues, as many are still holding water. A technician
uses a dipper to take a sample of the water and visually inspects
it for mosquito larvae. If larvae are present, the technician
transports the sample to the laboratory for counts and
identification. This April, 120 larval samples were submitted to
the laboratory. The most frequently occurring species in larval
samples was Culiseta incidens, the cool weather
mosquito, present in 52 of the 120 samples.
The following table and graph show the average number of
mosquitoes collected per CO2 trap per night during the
month of March compared to the five-year average for the six most
common mosquito species in San Mateo County. Counts for all
species are averaging below five per trap night, which is
consistent with the five-year average. Culex pipiens
abundance is substantially lower than average (0.43 compared to
4.25). Typically, adult mosquito abundances for most species
begin to rise in April, and remain elevated until fall.
Surveillance for mosquito larvae in seasonal impounds and marsh
sources continues to be a priority, as on-and-off rainfall has
kept them full of water. A technician uses a dipper to take a
sample of the water and visually inspects it for mosquito larvae.
If larvae are present, the technician transports the sample to
the laboratory for counts and identification. This March, 120
larval samples were submitted to the laboratory. The most
frequently occurring species in larval samples was Culiseta
inornata, the winter marsh mosquito, present in 42 of the 91
samples.
