What to do about mosquitoes as September swelters (original) (raw)

Hand crews descended on a residential neighborhood in Oceanside Tuesday morning, spraying pesticides to kill mosquitoes after a resident in the area tested positive for dengue virus infection.

Officials say that the person involved, who was not identified, became infected during travel, but declined to specify a destination. Tuesday’s spraying is designed to eliminate any mosquitos that may have bit the patient while they were infected, potentially becoming infected by feeding on their blood.

Nationwide, public health departments are acting out of an abundance of caution as dengue, often called dengue fever, caused an international outbreak with an estimated 11 million cases in North, Central and South America.

Concerns over West Nile virus, also carried by the tiny aedes aegypti mosquito that has now become annoyingly common San Diego County, have also flared this summer, with an increasing number of cases popping up on the East Coast, even infecting and briefly hospitalizing Dr. Anthony Fauci, former director of the National Institute of Allergy and Infectious Disease.

A container with mosquito larva collected from San Diego. (Nelvin C. Cepeda / The San Diego Union-Tribune)

Mosquitoes of the Culex species spread West Nile, though the region has not recorded a human case so far this year.

Preventing mosquito bites has become more necessary in San Diego County since 2015, when aedes first arrived in what biologists say is a northward migration driven by climate change.

Research shows that hot weather can turbocharge mosquito reproduction.

Finding and eliminating hatching locations can reduce the number of biters this fall.

But mosquito eggs need standing water to hatch and, given that San Diego County has not recorded rainfall since early May, any biting going on this summer comes down to insect breeding in caches fed by man-made sources.

Mosquitoes are known to reproduce in tiny pools of stagnant water, notes Allison Bray, the supervisor of the county’s Environmental Health and Quality Vector Control Program.

“Aedes mosquitoes are so comfortable around people that they will actively breed inside houses if they have an opportunity,” Bray said. “We’ve seen them in bouquets of plants in a vase, toilets with a clogged drain, pet water bowls that have been sitting while people have been on vacation.

“They’ll pretty much go for anything.”

The county offers a free investigation service staffed with technicians trained in ferreting out hidden mosquito breeding locations.

Stacey Mesler (l) with San Diego County Vector Control demonstrates for Anna Kremen (r) to inspect empty plant containers for possible water. Nelvin C. Cepeda / The San Diego Union-Tribune)

Technician Stacey Mesler conducted a demonstration inspection at a county employee’s house last week using years of accumulated mosquito-hunting knowledge, and a simple flashlight to illuminate the hidden spots where trouble multiplies.

She immediately stopped at the Talmadge home’s curb, noting the circular opening of a drainpipe bisecting the vertical plane of the curb in front of the residence.

“See how there’s some debris in there,” Mesler said. “Sometimes, water can back up into the yard, especially if you have a French drain.”

Moving into the home’s backyard, she locates a circular green plastic grate covering a drain embedded in the backyard lawn next to a covered hot tub.

Pulling the cover off, her flashlight finds moisture even after months without rain.

“There’s a bit of water in there, and, you know, it’s not running water,” she says.

This is the kind of spot that technicians most-often find to be a hidden mosquito hatchery. It’s the same for the long drainage pipes that often run under yards and sidewalks, before reaching the curb.

People don’t realize, Bray explains, that those underground drainage pipes can retain small amounts of water.

“Mosquitoes are happy to fly down the pipe, lay their eggs in the pipe, and fly away,” she said.

Pulling off drain covers and interposing a fine mesh screen before pushing the cover back into place can prevent mosquitoes from gaining access to drains and their overflow piping. If an infestation is found, bacterial products can be used to kill larvae before they become adults.

In San Diego, these backyard drains tend to be installed to prevent backyard flooding during winter storms. Most homeowners, then, would expect them to be bone dry in the summer months. But most backyards also have irrigation. Overspray from sprinklers can supply a gradual but regular amount of moisture that most would not suspect could accumulate out of sight.

Buckets, fountains, even plants can also hold standing water, Mesler notes during her inspection. Potted plants pose a problem because they must be regularly watered, but most planters have holes in their bottoms to allow proper drainage. That means a small amount of water will escape at the base every time a potted plant is watered. Here, she notes, there is a very simple strategy to avoid creating an inadvertent mosquito breeding ground.

“You can use a fine sand around the base of a saucer,” she explains, using a natural material to absorb runoff and prevent a tiny pool of standing water from forming.

San Diego County Vector Control recommends with patio planters with a planter saucer, to add sand to the saucer, to prevent mosquitoes from laying their eggs in any remaining standing water. (Nelvin C. Cepeda / The San Diego Union-Tribune)

Sometimes, a significant source of breeding water may look secure but isn’t.

“Mosquitoes need standing water, something with a surface to it, because their larvae live in the water and they float to the top to breathe,” Bray said. “So something like wet soil or wet sand, it doesn’t work.”

In one case, Bray recalls, technicians searched and searched for the location of an infestation only to find that the buggers were boiling out of the water-filled base of a basketball goal. The plug meant to keep bugs out was missing, creating an ad-hoc mosquito incubator.

Rain barrels can be another unexpected source.

Sometimes, Bray added, the downspout from a home’s gutters will be piped directly into a rain barrel with a tight cap in place that makes it look like nothing could access the inside.

“People won’t realize that the mosquitoes will just fly right down the downspout from the gutter up at the eaves,” Bray said.

Fixing these less-than-obvious sources of dry weather water retention can vastly reduce mosquito problems on any given property. But sometimes experts cannot identify any clear source of water that is causing an infestation.

While statistics were not available on how many of the county’s investigations end without identifying a source, Bray said that aedes, the most annoying species currently around San Diego County, don’t travel too far — probably only around 500 feet.

So, if the source is not in the backyard of the person who calls for a consultation, it’s likely in a neighbor’s backyard.

Standard operating procedure, Bray said, is to offer investigations to the neighbors.

“Sometimes we will get replies from them where they’re like ‘yes, please come by,” Bray said. “And then other times people are like ‘no, I’m not interested in that.’

“And in those situations, we’ll never know if they had a small amount of water in their yard somewhere that was contributing.”

At Kit Carson Park in Escondido on Wednesday, Aug. 28, 2024, a helicopter flies over the large pond spreading granules during aerial operations for mosquito larvicide application. (Nelvin C. Cepeda / The San Diego Union-Tribune)

The county also funds mosquito prevention on a much larger scale, using helicopters to drop larvicide in local bodies of water where breeding may occur. The next drop is scheduled for Sept. 19.

Requests for service can be made by emailing vector@sdcounty.ca.gov or by calling (858) 694-2888.