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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Mosquito Larval Collections from January 2019

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, 207 larval samples were submitted to the laboratory. The most frequently occurring species in larval samples was Culiseta incidens, present in 78 of the 207 samples.

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January 2019 CO2 Trapping 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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Mosquito Larval Collections from December 2018

Surveillance of water for mosquito larvae increases after autumn rainfall, when marshes, impounds and natural ponds fill with 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 December, 41 larval samples were submitted to the laboratory. The most frequently occurring species in larval samples was Cs. incidens, from 21 out of 41 samples.

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December 2018 CO2 Trapping 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 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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November 2018 CO2 Trap Results

These table and graphs 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. All species are near or slightly below average for this time of year.

Species

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October 2018 CO2 Trap Results

The table and graphs below 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. Counts for all species are averaging below ten per trap, which is consistent with the five-year average.  Although Culex pipiens had a late peak in September, it has returned to normal levels, and we expect it to further decrease through the colder months.

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CO2 Trapping in September 2018
Average number of adult mosquitoes per trap

These table and graphs show the average number of mosquitoes collected per CO2 trap per night during the month of July and August compared to the five-year average for the six most common mosquito species in San Mateo County. The peak of Cx. erythrothorax, the tule mosquito, in July and August has subsided. Although the abundance is still above average, it should continue to lower as autumn progresses. Cx. pipiens, the northern house mosquito was collected in atypically high numbers during September. The high numbers of Cx.

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CO2 Trapping in August 2018

Species

July 2018

5-year July average

August 2018

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July 2018 CO2 Trapping Report
Average adult mosquitoes collected per trap per night

These tables and graphs 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.

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CO2 Trapping in June 2018
Average adult mosquitoes collected per trap per night

These table and graphs 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. All species increased in abundance during June, except Aedes sierrensis, which kept consistent numbers from May. The number of collected Culex pipiens, the most abundant summer mosquito, remains below average. This is likely a result of pro-active seasonal catch basin control, utilizing mapping software in the field for more effective treatments.

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CO2 Trapping for May 2018
Average adult mosquitoes collected per trap per night

This table and graphs show the average number of mosquitoes collected per CO2 trap per night during the month of May compared to the five-year average for the six most common mosquito species in San Mateo County. All species increased in abundance during May, except Aedes washinoi, which typically peaks in March and April. The number of collected Culex pipiens, the most abundant summer mosquito, is below average. This is likely a result of pro-active seasonal catch basin control, utilizing mapping software in the field for more effective treatments.

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CO2 Trapping
April 2018

This table and graphs show the average number of mosquitoes collected per CO2 trap per night during the month of April compared to the five-year average for the six most common mosquito species in San Mateo County. All species were collected in numbers averaging less than five per trap, which is typical for April. Although mosquito trap counts are slightly higher than in March, the cool temperature at night through April combined with control efforts has kept adult mosquito abundance low.

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CO2 Trapping
March 2018

This table and graphs 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. All species were collected in numbers averaging less than five per trap, which is typical for March. Mosquito species that typically emerge in spring, such as Aedes sierrensis and Culex erythrothorax, have not yet been detected in traps, probably because cool and wet wintry weather continued through March.

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CO2 Trapping
February 2018

The table below shows the proportions of common mosquitoes in San Mateo County that were collected in carbon dioxide baited traps in February 2018, compared with the five-year average during February.

Species

February 2018

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CO2 Trapping
January 2018

The table below shows the proportions of common mosquitoes in San Mateo County that were collected in carbon dioxide baited traps in January 2018, compared with the five-year average during January.

Species

January 2018

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CO2 Trapping
December 2017 and all-year

The table below shows the proportions of common mosquitoes in San Mateo County that were collected in carbon dioxide baited traps in December 2017, compared with the five-year average during December.

Species

December 2017

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CO2 Trapping
November 2017 and Year-to-Date

The table below shows the proportions of common mosquitoes in San Mateo County that were collected in carbon dioxide baited traps in November 2017, compared with the five-year average during November.

Click on the graphs to see the year long monitoring data of the average number of mosquitoes captured in CO2 traps per night throughout 2017 and the five-year average for each month of the year. 

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CO2 Trapping
October 2017 and Year-To-Date

The table below shows the proportions of common mosquitoes in San Mateo County that were collected in carbon dioxide baited traps in October 2017, compared with the five-year average during October.

Click on the graphs to see the year long monitoring data of the average number of mosquitoes captured in CO2 traps per night throughout 2017 and the five-year average for each month of the year. 

  

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CO2 Trapping
September 2017 and Year to Date

The table below shows the proportions of common mosquitoes in San Mateo County that were collected in carbon dioxide baited traps in September 2017, compared with the five-year average during September.

Click on the graphs to see the year long monitoring data of the average number of mosquitoes captured in CO2 traps per night throughout 2017 and the five-year average for each month of the year.  

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CO2 Traps
July and August 2017, and Year to Date

The table shows the proportions of common mosquitoes in San Mateo County that were collected in carbon dioxide baited traps in July and August 2017 compared with the five-year average during July and August

Species

July 2017

Commands