Workers in San Mateo County and Santa Clara County will be out late Thursday night spraying for mosquitoes.
Late last week the vector control district found several mosquitoes carrying the West Nile Virus in the San Jose and Cupertino areas.
Insects on the Peninsula also tested positive for the virus. Those mosquitoes were found in Foster City, Belmont, Redwood City, Redwood Shores and San Mateo.
Crews will begin fogging on the Peninsula at 9 p.m. and in the South Bay at 11 p.m., weather permitting.