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2022 Mosquito Surveillance

Adult Mosquitoes

Smiling person in tan uniform attaching a mosquito trap (a red and white drink cooer with a small white PVC pipe and a bag made from netting) to a tree

All six of the most commonly collected mosquito species in San Mateo County averaged less than five collected per trap. Culex pipiens numbers are far below the average for this month (1.6 per trap compared to an average of 11.7). This low abundance is fortunate because Culex pipiens is an important vector of WNV in California. This species breeds in backyard and underground sources, and is a primary target of treatments by seasonal catch basin drivers and inspections by our vector control technicians.

Carbon-dioxide trap data

This 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.

SpeciesJune 20225-year June average
Aedes sierrensis2.50.6
Culiseta incidens2.41.9
Culex erythrothorax1.74.9
Culex pipiens1.611.7
Culex tarsalis1.60.9
Aedes washinoi0.41.4

 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

Side view of a person with short hair and a tan colored baseball hat and blue surgical mask on. The person appears to be standing in a field, with a bright yellow vest and holding a metal stick that has a white plastic cup on the end of the stick. The person is looking in the cup.

During the summer months, mosquito larval samples from seasonal impounds decline. Summer samples are often collected from residential areas, such as backyard fountains and fish ponds, water under buildings, storm drains, other containers in yards, and treeholes. Some are also collected from pockets along creeks. 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.

This June, 113 larval samples were collected in the field by vector control technicians and submitted to the lab. The collected larval samples contained larvae from nine different mosquito species. Larval samples in June were dominated by Culiseta incidens, present in 83 of the 113 samples (73%). 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. This data provides a record of the species present from a residential source and is helpful in detection of introduced species.

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