Quick Take
As Santa Cruz County’s mosquito control program seeks more funding from voters, an invasive species of disease-carrying mosquito is resurfacing in Boulder Creek, two years after it was eradicated from the area.
Two years after first detecting yellow fever mosquitoes in 2022, Santa Cruz County workers successfully eradicated the species. Now, less than a month before voters decide whether to increase funding for the program, the mosquitoes are back.
Santa Cruz County Mosquito and Vector Control this week confirmed the presence of the invasive Aedes aegypti mosquito in Boulder Creek. The species is a concern due to its potential to transmit viral infections like dengue, Zika and yellow fever.
In response to the detection, county staff are working to identify the scope of the infestation and prevent its spread by deploying specialized traps and sampling water in the downtown Boulder Creek area.
“We’re still in the discovery phase of understanding how far and wide the infestation is,” said assistant vector control manager Amanda Poulsen. Suspicions about an infestation were first raised after her team made a troubling find during routine surveillance last week.
A familiar-looking mosquito had turned up in one of the team’s traps, raising concerns that the invasive species might have returned to the county. The mosquito was soon confirmed to be Aedes aegypti by the California Department of Public Health.
The species is far more aggressive than local mosquitoes and often identified from community reports rather than traps.
Following the discovery, Poulsen’s team quickly expanded monitoring efforts in hopes of rooting out any more of the species. So far, none have been identified.
The discovery comes just weeks after property owners in the county were first asked to approve an increase in annual fees to fund the county’s Mosquito and Vector Control program. The benefit assessment, which hasn’t been increased since 2005, is designed to help deal with infestations like the one Poulsen’s team is tackling right now.
Santa Cruz County property owners will vote by Nov. 4 whether to approve the tax hike. Poulsen underlined the importance of increased funding to managing future infestations. The funds would allow the team to purchase specialized equipment and hire seasonal staff to respond effectively to future detections of invasive mosquitoes.
“Our teams are already spread pretty thin,” Poulsen said, explaining that officials in the program have been working extra hours to monitor and respond to last week’s detection. “I can’t imagine if we have, say, two of these detections happen at the same time. With just our current staffing and current income from the current assessments, we don’t have the capacity to respond to all of those at once.”
Aedes aegypti has been moving its way up California in the past few years and has spread significantly into the Central Valley and into Southern California, where it was responsible for the first locally transmitted case of dengue in the state.
Long-term climate trends point to more of California becoming habitable for the mosquito. In 2022, the detection of Aedes aegypti in Watsonville prompted swift action by the county, which was able to fully eradicate the species from the area.
Compared to local mosquitoes, the invasive species presents unique challenges. For one, it’s not as drawn to traps.
“Even when we use specialized lures, which we did for all the traps we put out last week, they’re pretty good at hiding,” Poulsen said. “If you have 100 of these mosquitoes, you’re lucky if you get one in a trap.”
Difficulty in trapping the species means that it takes more time and effort to determine the scope of a new infestation. As Poulsen also described, the breeding habits of Aedes aegypti make combating its spread far more difficult.
While local mosquitoes prefer specific places to lay their eggs, like slough systems and storm drains, Aedes aegypti gravitate to small bodies of water in backyards, meaning that finding and eliminating invasive eggs is harder.
Poulsen’s team is currently investigating homes around Boulder Creek to look for evidence of the invasive species, working with locals to check puddles and bird feeders in backyards around town.
Mosquito and Vector Control is also urging residents to review best practices on how to prevent the spread of invasive mosquitoes in Boulder Creek and beyond. The team is directing residents to give special attention to their septic tanks, which can be hot spots for mosquito breeding. In addition, residents can submit service requests to direct the search for invasive species.
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