Mosquito Season is Back; County Conducts First Larvicide Drop of 2017

The County of San Diego’s Vector Control Program will drop its first batch of larvicide of the year on 48 rivers, streams, ponds and other waterways to kill mosquito larvae Wednesday. (Update 4/19/17: Conditions did not allow all sites to be treated Wednesday. Remaining sites will be treated Thursday.)

Vector Control uses a helicopter to treat the waterways roughly once a month from April/May through October with a granular larvicide to control mosquito populations and protect the public from mosquito-borne illnesses like West Nile virus. The larvicide is harmless to people and pets but kills mosquito larvae before they can turn into biting adults.

The waterways total just over 1,000 acres and stretch from Chula Vista in the south to Fallbrook in the north and from Oceanside in the west to Lakeside in the east.

The County’s Vector Control Program also treats another 1,400 potential mosquito-breeding areas each year by hand, gives out free mosquito-eating fish to the public, tracks down and treats neglected swimming pools, tests dead birds for West Nile virus, and monitors cases of another potential mosquito-borne illness, the Zika virus.

The County has also called on the public to help fight two types of invasive Aedes mosquitoes because they have the capability to transmit Zika and other tropical diseases if they first bite an infected person, and because they like to breed outside of the County’s larvicide targets — in people’s yards and inside homes.

Because of that, County officials have urged people to find and dump out any standing water inside and outside homes, to keep invasive Aedes mosquitoes from breeding.

Zika and other tropical diseases, including chikungunya and dengue, are not naturally found in San Diego County. But county residents who visit countries and places where these diseases are established can return home infected, where invasive Aedes mosquitoes could bite them and spread disease to others.

In 2016, 82 county residents tested positive for Zika after traveling abroad. In 10 instances, County Vector Control found invasive Aedes mosquitoes living near people who contracted Zika. To make sure those mosquitoes could not spread Zika to others, Vector Control hand-sprayed people’s yards in 10 neighborhoods to kill mosquitoes and protect the public.

County officials said to fight mosquitoes and mosquito-borne illnesses including West Nile virus and Zika, residents should always follow the County’s “Prevent, Protect, Report” guidelines.

Prevent mosquito breeding

Dump out or remove any item inside or outside of homes that can hold water, such as plant saucers, rain gutters, buckets, garbage cans, toys, old tires, and wheelbarrows. Mosquito fish, available for free by contacting the Vector Control Program, may be used to control mosquito breeding in backyard water sources such as unused swimming pools, ponds, fountains and horse troughs.

Protect yourself from mosquito bites

Protect yourself from mosquito-borne illnesses by wearing long sleeves and pants or use repellent when outdoors. Use insect repellent that contains DEET, picaridin, oil of lemon eucalyptus, or IR3535. Make sure screens on windows and doors are in good condition and secured to keep insects out.

Report possible mosquito activity

Report increased mosquito activity, or neglected, green swimming pools and other mosquito-breeding sources, as well as dead birds — dead crows, ravens, jays, hawks and owls — to environmental health’s Vector Control Program by calling (858) 694-2888 or emailing Also report if you are being bitten by mosquitoes during daylight hours, or if you find mosquitoes that match the description of invasive Aedes mosquitoes by contacting the Vector Control Program at (858) 694-2888.

For more information, go to the County’s Fight the Bite webpage.



Gig Conaughton is a communications specialist with the County of San Diego Communications Office. Contact