Mosquito control officials say most of the region's West Nile Virus activity is happening in that area with many infected dead birds and positive mosquito samples.  

Luz Maria Rodriguez is with the Sacramento-Yolo Mosquito and Vector Control District.

"We'll be conducting the aerial spraying between 8 PM and midnight weather permitting. If people would like to stay indoors or if they would like to close their windows they can. It's not necessary but those are two precautions that they can take if they would like to."

More than 32,000 acres will be treated with Evergreen 60-6…both tonight and tomorrow night. It's an insecticide registered for use in mosquito control with the Environmental Protection Agency.

Rodriguez says they spray less than an ounce per acre…an amount so small it doesn't pose any health risks to humans.

So far this year, 40 dead birds and more than 160 mosquito samples have test positive for West Nile virus.