Wet Winter Expected to Bring Increased Mosquito Populations to Northern California

Following a wet winter in Northern California, public health and agricultural experts are warning residents of an expected increase in mosquito populations compared to the past three years. The previous years’ drought led to fewer mosquito breeding spots, but this year’s heavy rain and snowmelt have created ideal conditions for these pests.

While it’s still unclear how this will impact the overall mosquito season, it’s important to note that these insects have a wide range of ecosystems they infest, including high elevations and cooler climates. This means that areas like the mountainous Siskiyou County or Sierra Nevada will likely also see an uptick in mosquito activity.

Mosquitoes breed in areas with standing water, even as little as that in tree holes or containers. While some species are only active in the spring, others can breed throughout the warmer months. Female mosquitoes require a blood meal to produce eggs, and their bites can cause itching and potential disease transmission.

Two invasive species, Aedes aegypti and Aedes albopictus, were detected in Northern California in 2020. These species are known to transmit diseases including yellow fever and the Zika virus. Although no cases of mosquito-related illnesses have been reported in California this year, thousands of people have been infected with these diseases in Mexico, the Caribbean, Central and South America. Five other species, including two capable of spreading the West Nile virus, are of significant concern in Shasta County.

West Nile virus, transmitted through mosquito bites, can cause illness and occasionally death in humans, horses, and birds. Since 2003, over 7,000 human cases and more than 300 deaths from West Nile virus have been reported in California.

Residents can take steps to protect themselves from mosquitoes. This includes eliminating standing water where mosquitoes can breed, wearing mosquito repellent, ensuring window screens are in good repair, and avoiding outdoor activities at dusk and dawn when mosquitoes are most active. If mosquito populations start to increase significantly, especially disease-spreading species, vector control teams will begin spraying to control the adult mosquito population.