Also serving the communities of De Luz, Rainbow, Camp Pendleton, Pala and Pauma

County conducts first mosquito-fighting larvicide drop of 2023

Gig Conaughton

County of San Diego Communications Office

San Diego County was scheduled to conduct its first routine aerial larvicide drop of the year this week on up to 51 local waterways to help stop mosquitoes from potentially spreading diseases like West Nile virus.

County officials said helicopter larvicide drops will be done Wednesday, April 26, and Thursday, April 27, if necessary, to cover nearly 1,300 acres of hard-to-reach potential mosquito breeding areas. [In Fallbrook, the drop will happen at Lake Rancho Viejo, east of I-15 and north of 76.]

The county started using helicopters to drop solid, granular larvicide on hard-to-reach areas of standing water in rivers, streams, ponds and other waterways where mosquitoes can breed, in the early 2000s after the West Nile virus arrived.

The county conducts the aerial larvicide drops roughly once a month from April through October. The larvicide does not hurt people or pets but kills mosquito larvae before they can grow into biting mosquitoes. The next scheduled drop is May 17 and May 18.

West Nile virus is mainly a bird disease. However, mosquitoes can pass the potentially deadly virus on to people by feeding on infected birds and then biting people.

West Nile virus' effect has been relatively mild in San Diego County in the past few years. Three or fewer people have tested positive annually since 2017. But it can still be dangerous, and people should avoid mosquitoes. There have been no West Nile virus detections to date in San Diego County this year, not in mosquito pools, animals or people.

The larvicide drops are just one part of Vector Control's Integrated Vector Management Strategy. County Vector Control also monitors over 1,600 potential mosquito-breeding areas each year and applies larvicide through a variety of strategies – aerial drops, boats, trucks and hand-crews.

It also 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 mosquito populations for potential mosquito-borne illnesses.

Public has an important role to play

County Vector Control officials are also reminding people to help protect themselves from mosquitoes in and around their homes by finding and dumping out standing water to keep the pests from breeding.

Protecting against mosquitoes has required more help from the public in recent years because several types of invasive Aedes mosquitoes have established themselves here. These mosquitoes can potentially transmit diseases not naturally found here, including Zika, dengue and chikungunya, if they become infected by biting a sick person and then feed on other people.

Unlike the native Culex mosquitoes that are more likely to transmit West Nile virus, invasive Aedes mosquitoes prefer to live and breed around people's homes and yards.

County Vector Control officials said the best way people can protect themselves from mosquitoes is to follow their "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 standing water sources such as unmaintained 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 insect 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 and dead birds

Report increased mosquito activity, or stagnant, unmaintained swimming pools and other mosquito-breeding sources, as well as dead birds – dead crows, ravens, jays, hawks and owls – to the County Department of Environmental Health and Quality's Vector Control Program by calling 858-694-2888 or emailing [email protected].

Also report if you are being bitten by mosquitoes during daylight hours, or if you find mosquitoes that look like invasive Aedes mosquitoes – small, black with white stripes on legs and backs – by contacting the Vector Control Program at 858-694-2888.

For more information about mosquito-borne illnesses, go to San Diego County's "Fight the Bite" website,


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