Based on mosquito abundance and surveillance data, Orange County Mosquito and Vector Control District staff will conduct residential adult mosquito control in the City of Santa Ana on September 10th, 11th, & 12th from 12:00 a.m. to 5:00 a.m.
Reducing the population of adult mosquitoes with public health pesticides (adulticides) that are registered by the US Environmental Protection Agency (US EPA) will be done if necessary to prevent human illness or suppress a heavy nuisance infestation of mosquitoes. The decision to use mosquito control applications either by truck-mounted, backpack or aircraft application equipment will be based on surveillance information or the documentation of West Nile virus or other mosquito-borne disease activity at a level that indicates a threat to human health. Either Ultra-Low Volume (ULV) adulticide treatments or Wide Area Larvicide Spraying (WALS) treatments will be conducted in concentrated areas most at risk for disease occurrence or where travel-related mosquito-borne disease cases have been identified.
This mosquito chemical spraying is paid for by property tax assessments.
ULV Adulticide Treatments – Key Drawbacks
These treatments target adult mosquitoes using very fine pesticide droplets sprayed from trucks or aircraft.
- Bystander Exposure Risks
ULV sprays can drift into residential areas, settling on lawns, patios, and outdoor furniture. People—especially children—may be exposed through skin contact or hand-to-mouth behavior. - Inhalation Concerns
People nearby may inhale pesticide particles, especially during ground-based spraying. The EPA uses models to estimate air concentrations in breathing zones. - Environmental Drift
Aerial spraying can result in pesticide drift beyond the target area, potentially affecting unintended zones and wildlife. - Short-Term Effectiveness
ULV treatments kill adult mosquitoes but don’t address larvae, so populations can rebound quickly unless paired with larvicide efforts. - Resistance Development
Repeated use of the same chemicals can lead to mosquitoes developing resistance, reducing long-term effectiveness. - Impact on Non-Target Species
Though ULV uses small amounts, there’s still concern about effects on pollinators like bees and butterflies, especially if spraying is done near blooming plants.
WALS (Wide Area Larvicide Spraying) – Key Drawbacks
This method targets mosquito larvae using biological agents like Bacillus thuringiensis israelensis (Bti), sprayed over large areas.
- Limited Immediate Impact
WALS doesn’t kill adult mosquitoes, so it may not provide quick relief during outbreaks. - Residue Concerns
Fine mist droplets may leave a light residue on outdoor surfaces. While considered safe, some residents may find this undesirable. - Access Limitations
WALS is used to reach hidden breeding sites, but it still may not cover all areas, especially private backyards or inaccessible zones. - Cost and Logistics
Large-scale WALS operations require specialized equipment, nighttime spraying schedules, and ongoing monitoring, which can be resource-intensive. - Public Perception and Trust
Even though Bti is considered safe, some residents may be wary of any spraying near their homes, especially if not well-informed.