Oct 7 2026

Overnight Mosquito Treatments in Altadena and Monterey Park

Overnight Mosquito Treatments in Altadena and Monterey Park

If you heard a slow-moving truck on your street in the middle of the night this week, it wasn’t the trash crew. The San Gabriel Valley Mosquito and Vector Control District (SGV Mosquito) is running truck-mounted mosquito treatments in parts of Altadena and Monterey Park in the pre-dawn hours of Wednesday, Oct. 7 and Thursday, Oct. 8.

The goal is simple: knock down mosquito populations that the district says pose a real public health risk, and cut the chances of mosquito-borne illness like West Nile virus spreading as the season winds down. Here’s what’s happening, where, and what it means for you.

When and where

Treatments run between midnight and 5:30 a.m. on both Wednesday, Oct. 7 and Thursday, Oct. 8, according to the district’s Oct. 3 announcement.

Community Treatment area Products
Altadena Between Glenrose Ave. and Marengo Ave., south of E. Mariposa St. and north of W. Woodbury Rd. Adulticide (AquaDUET) + larvicide (VectoBac WDG)
Monterey Park Between W. Floral Dr. and the 60 Freeway, east of Vancouver Ave. and west of Collegian Ave. Adulticide (AquaDUET)

The district’s announcement includes an interactive map of each zone. If weather doesn’t cooperate or there are operational delays, the treatments can be pushed back, so check the district’s site or social channels for updates.

Why now

West Nile virus has had a busy year in the valley. As of the district’s Sept. 28 update, 177 mosquito samples across the San Gabriel Valley had tested positive for the virus in 2026, along with 11 dead birds.

Monterey Park stands out: 14 positive mosquito samples since late July, tied with Alhambra and behind only West Covina (18) and Covina (17). It also has two positive dead birds. Altadena has logged three positive samples since July 23.

The Oct. 3 announcement doesn’t name a single trigger, but the district treats area-wide spraying as a step it takes when mosquito numbers or disease risk cross a set threshold. Altadena is also part of the district’s ongoing Eaton burn area response, a dedicated mosquito-control effort in the fire zone.

West Nile is endemic to Los Angeles County, meaning it turns up every year. Warm fall weather keeps mosquitoes active well into October, so the season isn’t over yet.

What’s being applied

Crews are using two products that hit mosquitoes at different stages of life:

  • AquaDUET (both areas) is an ultra-low-volume adulticide aimed at flying adult mosquitoes. Its active ingredients, sumithrin and prallethrin, are synthetic versions of compounds found in chrysanthemum flowers. It’s water-based, so the district says it won’t damage car or house finishes.
  • VectoBac WDG (Altadena only) is a biological larvicide made from the bacterium Bacillus thuringiensis israelensis (Bti). It’s applied to water holding mosquito larvae so fewer of them grow into biting adults.

Hitting both adults and larvae is meant to break the breeding cycle rather than just thin out tonight’s swarm. For common questions about safety, pets and gardens, see the district’s area-wide treatment FAQ.

What you can do

Spraying helps, but the district is clear that mosquito control is a shared job. A few minutes of yard checks each week goes a long way.

Cut off breeding spots

  • Dump anything holding water for more than a week: clogged gutters, buckets, old tires, plant saucers, rain barrels.
  • Keep pools, spas and ponds maintained and circulating.
  • Refresh pet bowls and birdbaths weekly.
  • Report neglected or green pools to SGV Mosquito through its tip form.

Avoid bites

  • Use an EPA-registered repellent with DEET, picaridin, IR3535 or oil of lemon eucalyptus, and reapply as the label directs.
  • Wear light-colored long sleeves and long pants outdoors, especially around dawn and dusk.

Stay informed

The district posts notices in treatment areas and shares updates on social media, Nextdoor and local news. To get alerts directly, sign up for SGV Mosquito e-alerts.

Sources

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