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. This mosquito is found year-round in a variety of sources, especially backyard fountains and fish ponds. It is not known to transmit diseases. Culiseta inornata, the winter marsh mosquito, was also collected frequently this past month.  This mosquito is large and conspicuous but only infrequently bites humans. Aedes dorsalis is a mosquito of particular concern due to its aggressive biting behavior.  This mosquito was collected from salt marsh sources along the San Francisco Bay this March, and technicians are regularly monitoring these sites to prevent spring emergence of adults.