Mosquito Surveillance

Overview

How to Interpret Mosquito Surveillance Data

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.

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March 2020 CO2 Trap Results

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. The numbers are expected to remain low until after spring rains.

Species

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Mosquito Larval Collections from March 2020

Surveillance for mosquito larvae is a priority in late winter and early spring, as seasonal water sources fill with rain 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, 109 larval samples were submitted to the laboratory. The most frequently occurring species in larval samples was Culiseta incidens, the cool weather mosquito, present in 48 of the 109 samples.

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Mosquito Larval Collections from February 2020

Surveillance for mosquito larvae is a priority in the winter, as seasonal water sources have filled with rain 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 February, 91 larval samples were submitted to the laboratory. The most frequently occurring species in larval samples was Culiseta incidens, the cool weather mosquito, present in 38 of the 91 samples.

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February 2020 CO2 Trap Results

The following table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of February 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. The numbers are expected to remain low until spring.

Species

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Larval Mosquito Collections from January 2020

Surveillance for mosquito larvae is a priority in the winter, as seasonal water sources have filled with rain 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 January, 175 larval samples were submitted to the laboratory. The most frequently occurring species in larval samples was Aedes washinoi, present in 70 of the 175 samples.

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January 2020 CO2 Trap Results

The following table and graph show the average number of mosquitoes collected per CO2 trap per night during the month of January 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. The numbers are expected to remain low until spring.

Species

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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.

 

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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.

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November 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 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.

 

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Larval Mosquito Collections from November 2019

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.

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October 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 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.

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Larval Mosquito Collections from October 2019

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.

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September 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 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.

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Larval Mosquito Collections from September 2019

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.

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August 2019 Carbon dioxide baited trap results

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.

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Larval mosquito collections from August 2019

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.

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July 2019 Carbon dioxide baited trap results

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.

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Larval mosquito collections from July 2019

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.

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June 2019 Carbon dioxide baited trap results

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.

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Larval mosquito collections from June 2019

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.

Commands