In the 2019 calendar year, the District closed out one of its
lowest seasons for West Nile virus activity since the virus first
appeared in San Mateo County in 2004. No virus was detected
in the county this year in any of the standard WNV surveillance
indicators.
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 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.
