The Alameda County Mosquito Abatement District is dedicated to protecting the public from both the discomfort of mosquito bites and potential mosquito-borne diseases. This responsibility includes monitoring the abundance of adult and immature (larval/pupal) mosquitoes, and mosquito-borne disease occurrence over time and space. The practice of monitoring both mosquito densities and the diseases they carry is termed surveillance. Surveillance provides the District with valuable information on what mosquito species are present, when they occur, where they occur, how many there are, and if they are carrying diseases that affect humans. Equally important is the use of surveillance in evaluating the effectiveness of control actions in reducing mosquitoes and mosquito-borne diseases.

How is mosquito surveillance and monitoring conducted?

Larval surveillance

District technicians inspect known mosquito breeding sites a regular basis. Larval surveillance is conducted by the use of a “dipper.” This is a one pint cup attached to the end of a stick. Water is dipped or sampled for the presence of mosquitoes. Samples are examined in the field or laboratory for the abundance, species, and life-stage of mosquitoes present. This information is compared to historical records and used as a basis for treatment decisions.

Adult surveillance

Adult mosquito surveillance is done for two primary reasons. First, it allows the technician to locate new, undiscovered sources of larval breeding, or calls attention to the fact that a known larval breeding source needs to receive closer inspection and treatment. Second, the collection of live adult mosquitoes is useful to see where certain species of mosquitoes are and/or for virus testing. Adult populations are sampled using several trap types , such as:

1. Carbon dioxide baited trap/BG-Sentinel - uses dry ice to gradually release carbon dioxide to mimic humans and mammals breathing. This attracts host-seeking female mosquitoes who need to feed on blood to be able to produce eggs. 

• These traps are placed throughout Alameda County to capture mosquitoes and collected the next day. 

Disease Surveillance and Testing

The District participates with the California Department of Public Health (CDPH) and the University of California in performing surveillance for mosquito-borne diseases, especially West Nile virus. The District's program is an early warning system that allows for timely response and appropriate mosquito control treatment efforts in Alameda County. 

Mosquito Testing

The Alameda County Mosquito Abatement District collects mosquitoes through adult mosquito surveillance methods, such as carbon dioxide baited traps, and test them at our laboratory facilities. When testing criteria and guidelines are met, female mosquitoes of specific species are tested for mosquito-borne diseases, such as West Nile virus (WNV),  St. Louis and Western Equine Encephalitis.

Dead Bird Surveillance Program

The District is a part of the California Department of Public Health (CDPH) Dead Bird Surveillance program where dead birds are tested for West Nile virus (WNV) when it meets testing criteria. Dead bird reports are used to track where WNV could be spreading.

If you find a bird that has recently died in Alameda County, please call the CDPH WNV Call Center at 1-877-WNV-BIRD (April - October) or file an online report.