January 2020 District Newsletter

New from the District in January: New Year, New Mosquito Worries

Click here to read the January 2020 District Newsletter.


West Nile Virus Update – December 2019

San Mateo County

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.

Surveillance Factor

Previous 10-year average (2009-2018)


Larval Mosquito Collections from December 2019

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.


December 2019 CO2 Trap Results

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.



Invasive Aedes Mosquitoes


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Report a Dead Bird


Board Meeting Agendas