At first glance, it appears as if Vince Sanchez is looking at a cup of water with a floating clump of dirt inside. It’s only through a microscope that the particles – some 200 eggs – come into focus.
These eggs will hatch within a few days into larvae, wiggly spindles barely large enough to see with the naked eye. They’ll live at the surface of a pool of water for several days, shedding their skin four times before molting and changing into a pupa. It’s here that an insect grows before splitting open the pupa casing, emerging as an adult.
It’s a metamorphosis story, but not for a beautiful animal. It’s the life cycle of a mosquito to adulthood, and adults will eat nectar from flowers. It’s only the females that bite, sucking blood for protein to use for their eggs to repeat the whole cycle again.
In hot Central Valley summers, the whole process, from egg to adult, happens in as little as four days; in Monterey County, it’s generally closer to two weeks. Keeping them cold can slow the process down to two months, so Sanchez – the public education coordinator for the Northern Salinas Valley Mosquito Abatement District – keeps a refrigerator of large Tupperware containers of water, where he’s cooling and slowing the life cycle. The larvae make for good educational props.
“People call these pollywogs, leeches, shrimp, worms. I’ve heard everything,” Sanchez says, looking at wiggling larvae. “People see them in the backyard and think they’re tadpoles.”
They are, in fact, none of those. There are 18 species of mosquitoes that live in Monterey County, a fraction of the 60 in California and 3,500 species worldwide. In the eyes of Sanchez and his colleagues at the Mosquito Abatement District, they’re not just pests that buzz annoyingly and administer itchy bites, they’re vectors for disease. And for that reason, the district is on a mission to eliminate as many mosquitoes as possible.
“There’s no benefit of a mosquito that has been proven,” Sanchez says. “All they bring is a nuisance, and in a lot of cases, death.”
THE MOSQUITO PRE-DATES HUMAN HISTORY, estimated to have first appeared on Earth 190 million years ago, compared to 5 to 7 million years ago for humans. The diseases they transmit have been similarly present, shaping human history.
“Flying solo, the mosquito does not directly harm anyone. It is the diseases she transmits that cause an endless barrage of death. Yet without her, these pathogens could not be vectored to humans. Without her, human history would be completely unrecognizable,” Timothy Winegard writes in The Mosquito: A Human History of Our Deadliest Predator, published in August. “The mosquito and her diseases have accompanied traders, travelers, soldiers and settlers (and their captive African slaves) around the world and have been far more lethal than any manufactured weapons or inventions.”
Mosquitoes are responsible for carrying ailments including Zika, West Nile virus, dengue, yellow fever, chikungunya, malaria – the latter killing hundreds of thousands of people every year.
“Mosquitoes are one of the deadliest animals in the world,” according to the World Health Organization. “Their ability to carry and spread disease to humans causes millions of deaths every year.”
According to the WHO, mosquito control globally peaked in popularity in the 1940s and ’50s, then waned. “As so often happens in public health, when a health threat subsides, the control program dies. Resources dwindled, control programmes collapsed, infrastructures dismantled, and fewer specialists were trained and deployed.
The mosquitoes – and the diseases they transmit – roared back with a vengeance.”
Dengue fever, for example, has increased 30-fold in the last 50 years. In the U.S., West Nile virus – the leading cause of mosquito-borne illness here – was first detected in 1999. It appeared in California in 2003, and within a year, was detected in all 58 California counties.
The numbers of mosquito-borne illnesses are much lower in the U.S. than in other places around the world, where millions of people become infected annually. For example, 10 cases of West Nile virus in humans were reported in six California counties in 2018. The most recent reported case in Monterey County was in 2017.
The WHO has investigated genetically modified mosquitoes and the mass release of sterilized male mosquitoes as possible methods of control in recent years.
For its part, the Northern Monterey County Mosquito Abatement District relies largely on larvicide and mosquito-eating fish. Many mosquito species don’t bite humans, and not all that do carry disease. In Monterey County, the district regularly sets traps in search of Culex pipiens, which carry West Nile virus. The district also is on the lookout for bluish-greenish Aedes sierrensis, which transmit dog heartworm, and watching for Aedes aegypti, which transmit yellow fever and has been found elsewhere in California.
Because they are a vector-control agency imbued with powers to protect public health, district officials can alter the landscape without stopping to conduct an environmental review of each project. They can remove vegetation along waterways, apply pesticides and introduce fish that consume large numbers of mosquito larva to keep the population in check.
IT’S A HOT SUMMER DAY and Paul Palomo, a senior mosquito control technician, rolls up to a gated house in Prunedale off Vierra Canyon Road. If there wasn’t a gate, he might just walk right up to the pool, or what’s left of it, but the homeowner here is expecting him.
Marta Montenegro has lived here for more than 20 years, and has never filled the pool; she didn’t want to run her well dry, or to pay for electricity to pump enough water to fill it. She likes keeping it around for potential water emergencies as a backup source. Besides, if she ever sells the house, she expects the pool will add value. So for decades it’s been mostly empty, now with about three feet of greenish brown water in the deep end, and a sunken umbrella on its side.
The district found Montenegro’s pool because for the first time, the district this summer hired an airplane for $10,000 to fly over its 458 square miles, covering the northern half of Monterey County and the Monterey Peninsula, looking for evidence of old and abandoned pools – prime breeding grounds for mosquitoes, which lay eggs in standing water. From the plane, they identified 330 pools that showed up as questionable, then narrowed down the list to about 100 and sent letters to property owners advising them to drain their backyard swamps. (Most property owners cooperated; for those that didn’t, the district secured an abatement warrant from Monterey County Superior Court, granting permission to access the property without an owner’s permission.)
Palomo inspects Montenegro’s pool, dipping a strainer attached to a long pole, and pulls up a few tadpoles. As he walks the perimeter, he tries a few more times, examining the contents of his strainer, and then he sees some hatched pupa casings – not live mosquitoes, but evidence that they’ve been here recently.
Montenegro says mosquitoes aren’t a problem, but Palomo offers to drop in mosquito fish for free. He goes back to his truck, where he’s got a bucket of the guppy-sized gray fish, and drops three into the pool; then he opts for another two – some mosquitoes might hide under the sunken umbrella.
Each fish eats about 100 mosquito larvae a day, and unlike most fish, they reproduce live offspring, rather than laying eggs, meaning the population of five is likely to grow fast. “If there’s nothing left, they’ll eat their own young,” Palomo adds.
Montenegro is indifferent to the fish and mostly surprised to learn the Mosquito Abatement District exists. She looks at the letter she received after their flyover, threatening fines of $1,000 a day. “It really caused me anxiety,” she says, adding she went to the district office in person, because she suspected the letter, which had no return address, might be fraudulent.
Palomo thanks her for the feedback. “This was our first time doing it, so we didn’t perfect it,” he says.
Gambusia have been so effective at eliminating mosquitoes in some places, including Corsica, Italy and Sochi, Russia (where malaria was devastating until the mid-20th century) that there are statues honoring the fish.
BACK AT THE MOSQUITO DISTRICT OFFICE, Buddy the bearded dragon – “he’s our mascot, I guess,” Sanchez says – crawls across the floor toward Sanchez’s desk.
Buddy is one of a few critters unrelated to mosquitoes that Sanchez keeps around because he likes them, and because he finds them engaging to bring to school presentations. There are leopard geckos Kona and Kai, a tank full of hissing cockroaches from Madagascar and Coco the boa. Sanchez does about 180 presentations a year at schools and events, trying to tell people about free services available from the district, and delivering the message to eliminate standing water.
In a garage, there’s a fleet of immaculate vehicles, and a line of tractors. Pallets are piled with bags of Bacillus thuringiensis, a bacteria strain first discovered in creek bottoms in Israel. It’s toxic to mosquito larvae, and is dropped into water on ground-up corn cob granules, which filter-feeding larvae eat. The district also sometimes applies larvicide oil, often by airplane (and they’re working on securing drone pilot licenses), which has the effect of suffocating larvae as they try to cling to the surface of a pond.
Out back, thousands of mosquito fish are breeding in tanks. When technicians go out on calls, they stop by and fill a bucket with some fish to deliver.
A plastic bag with a dead crow has just been delivered. The team will swab its throat and send it off to a lab in Berkeley to be sampled for potential West Nile virus, which hasn’t been detected locally for two years.
Buddy (the bearded dragon) is now crawling up a stack of papers. “He just runs around all day,” Sanchez says.
Most of the work done by four district technicians involves traveling around their territories, setting traps for mosquitoes and looking for standing water.
The district was created in 1950 in response to a surging mosquito population at Elkhorn Slough, where the salt marsh mosquito – the Aedes dorsalias, which can fly more than 20 miles – thrives in tidal conditions. “After the harbor was created, the ecology changed, and mosquitoes got so bad, they were devastating property values,” district manager Ken Klemme says. “It was so thick that farmers couldn’t farm – they were getting stuck in carburetors.”
The Monterey County Civil Grand Jury has twice investigated the district in the past 10 years, both times determining it should expand its efforts and jurisdictions. They’ve suggested the district expand its jurisdiction to serve Carmel Valley, Big Sur and South County.
In 2016, the Local Agency Formation Commission also recommended the district expand to encompass the whole county; Klemme says that’s unlikely because it would cost more for taxpayers. The district’s annual budget of $1.8 million is mostly funded with $7 parcel taxes, approved by voters with 66 percent of the vote in 2014. Full-county expansion would mean parcel taxes of closer to $40, Klemme says, because it’s such a large region geographically, so he has no intention of pursuing that advice and expanding. Instead, cities outside the district boundaries, like Gonzales, can contract for limited mosquito abatement services.
The office, across the street from the Salinas Municipal Airport, has been the district’s home for 66 years, rented from the city of Salinas. But with the threat of rent increasing from $1,100 a month to $3,600, they are facing potential eviction. Klemme expects to bring a final plan for extending the lease – or an exit strategy – to the board of nine governing members at an Oct. 10 meeting. Facing eviction, the district is currently in escrow to possibly buy a lot on Blanco Road, just up the street, as a Plan B; Klemme says they’d rather stay. “We built this thing and made it ours,” he says, “but we have no other option.”
PAUL PALOMO PULLS OFF OF HIGHWAY 1 into a marshy area near Castroville, part of his North County territory. He’s out looking for potential mosquito breeding grounds, and starts by leaving his truck running for a few minutes. Mosquitoes are attracted to carbon dioxide, the clue that guides them to mammals for a blood meal, and the truck exhaust has the same effect.
He continues on along a dirt road into constructed wetlands, and a great blue heron, an egret and a pair of ducks fly by. “It’s beautiful,” Palomo observes. “Sometimes I’ll come out here and have my lunch.”
He dips a strainer into the water of the Moro Cojo Slough a few times until he comes up with a few larvae in their fourth and final stage before hatching.
“This is the first time I’ve found them out here,” he says. “And it’s a lot. If there weren’t people actually out there treating mosquitoes, how bad would this place be?” he wonders.
He’ll probably send a helicopter out here to apply larvicide. Where possible, the district drops mosquito fish into contained pools or ponds, trying to avoid opportunities for the Florida natives to get out into the environment. Mosquito fish are opportunistic eaters, and while they start with mosquito larvae, they’ll eat other things – like tadpoles – if they’re out of larvae. The California Department of Fish and Wildlife publishes a guide for best practices to control mosquitoes without harming wetlands, and views the fish as preferable to insecticides, but with a caveat.
“[They] may reduce non-target populations of invertebrates or other mosquito predators,” according to CDFW’s guide, and “may negatively impact sensitive species.”
Seeing mosquitoes in a place he hasn’t before, Palomo talks about how the insects seem impossible to eliminate. “That’s the goal, but realistically it’ll never happen,” he says. “They’ve been here before us, they’ll be here after us. Really the goal is to keep disease out. We treat so many places, then the next year, it’s breeding again. We wonder, how did that happen?”