Two invasive (non-native) mosquito species have become established in many areas of California (PDF), especially southern California and the Central Valley. These mosquitoes are named Aedes aegypti (yellow fever mosquito) and Aedes albopictus (Asian tiger mosquito). Both species are small, black mosquitoes with white stripes on their back and legs. These mosquitoes only live near people and will use any small container that holds water, both indoors and outdoors, to lay eggs. Female Aedes mosquitoes bite during the day, and even a small number of mosquitoes can become an extreme nuisance. ​

Aedes aegypti and Aedes albopictus can transmit viruses to people when they bite, including dengue, chikungunya, and Zika. Currently, only dengue virus has been transmitted by mosquitoes in California, and this happens very rarely. However, dengue, along with chikungunya and Zika, are widespread in other parts of the world, including in Mexico, Central and South America, the Caribbean, and Asia. 

Protection and Prevention

People should protect themselves from Aedes mosquito bites while at home and during travel, especially when visiting tropical areas. EPA-registered mosquito repellents applied to clothes and exposed skin can help prevent bites. It is also important to dump and drain standing water (even very small sources of water) around your home to keep Aedes mosquitoes from breeding and spreading further in California.

People traveling in areas where dengue, chikungunya, and Zika viruses are present can become infected from mosquito bites. When they return to California, people who are infected can serve as sources for local mosquitoes to become infected and pass the virus to others. In this way, limited local transmission of dengue virus has occurred in California. Not everyone who becomes infected will get sick or remember being bitten while traveling. For this reason, it is important to use mosquito repellent for at least three weeks after returning home to prevent the spread of these viruses in California.