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2022 Mosquito Surveillance

Adult Mosquitoes

Unusually, Culex pipiens abundance has dropped over the spring, rather than rising. Throughout the year, Culex pipiens is consistently our most or second most frequently captured mosquito, but this April seasonal spring species are more abundant. Most notably, Culex erythrothorax was captured in high numbers, far above the five-year average for April. Most of these were collected from traps in the Sharp Park area of Pacifica. The counts of Aedes washinoi are also above average for this time of year. Aedes washinoi is an aggressive day-biting mosquito that feeds on mammals, including humans, but is not a significant vector for disease.

Carbon-dioxide trap data

This table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of Aprilcompared to the five-year average for the six most common mosquito species in San Mateo County.

 Data are shown for the six most common species found in San Mateo County.

SpeciesApril 20225-year April average
Culex erythrothorax13.50.5
Aedes washinoi6.21.7
Culex tarsalis4.10.7
Culiseta incidens3.30.6
Culex pipiens1.53.2
Aedes sierrensis0.61.9

 This chart shows the average number of adult mosquitoes collected in CO2 traps per trap per night night during 2022. Data are shown for the  six most common species of mosquitoes in San Mateo County.

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This chart shows the 5-year average number of mosquitoes collected per trap night by month for the previous 5 years. Data are shown for the six most common species found in San Mateo County.

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Larval Mosquitoes

This April, 154 larval samples were collected in the field by vector control technicians and submitted to the lab. A District vector control technician uses a dipper to take a sample of the water and visually inspects it for mosquitoes present. The technician then transports the sample to the laboratory for the larvae to be counted and identified.

The collected larval samples contained larvae from ten different mosquito species. Larval samples in April were dominated by Culiseta incidens, present in 121 of the 154 samples (79%). This mosquito is present year-round in San Mateo County and is frequently collected from fish ponds, containers holding water, and freshwater impounds. The high numbers of Culiseta incidens and total larval samples reflect an effort on the operations department to collect samples from residential sources. These data provide a record of the species present from a residential source and are helpful in detection of introduced species.

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