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News: 08/01/2019

Fires create new breeding grounds for mosquitoes, new workload for control district



neglected green swimming pool
For all the destruction wrought by the Nuns Fire in October 2017, it did produce an opportunity for new signs of life, hundreds of thousands of them, to be exact.

Unattended swimming pools, hot tubs, and ornamental ponds, septic tanks with melted lids, stagnant rainwater barrels and other water sources – all of them are potential breeding grounds for mosquitoes.

“In the days after the [North Bay] fires, we dealt with thousands of new sources [of mosquito production sites],” Marin-Sonoma Mosquito and Vector Control District Director Phillip Smith told the Board of Supervisors on Tuesday, July 23. That was on top of the 20,000 known sources of mosquito breeding grounds the district manages annually throughout Marin and Sonoma counties.

The district, founded in 1915, and funded by a benefit assessment on residents throughout those two counties, addresses public health concerns by managing the populations of mosquitoes and other disease-transmitting animals and insects like ticks, yellow jackets and rodents. The district gets about 4,500 calls annually requesting its services.

“Pools left untreated can generate hundreds of thousands of new mosquitoes every week,” Smith said. Even the folds in a pool cover can provide enough water for mosquito larvae. So, on high alert, district technicians coordinated with first responders and law enforcement and fanned out across the burn areas to document and treat these new potential breeding grounds.

In the weeks following the fires, the district added 64 new sites in Kenwood and 77 in Glen Ellen. In some instances, one property can have more than one production site.

There are 23 different species of mosquitoes found in Marin and Sonoma counties, and while the invasive Yellow Fever mosquito (Aedes aegypti) which has become established in Merced is not among them at the moment, there are five species here which can transmit West Nile virus, St. Louis encephalitis and dog heartworm – and all provide discomfort on a warm summer night.

“Our primary aims were to stop the breeding of mosquitoes that are capable of carrying West Nile virus and protect the safety and comfort of people working in the recovery zones,” said Smith. A mosquito’s lifecycle – egg, larva, and pupa – is rapid. Any item holding water for more than 72 hours has the ability to produce mosquitoes.

Unprotected and damaged pools were a major concern after the fires. In a non-fire year, field supervisors say they get an average of 20 to 40 calls about pools. “That number has definitely changed since the fires,” said Nizza Sequeira, public information officer for the district.

Treatments effective for each species of mosquito vary, but for the Culex tarsalis, Culex pipiens, Culex erythrothorax and Culex stigmatosoma – those capable of transmitting West Nile virus – field technicians treated pools with cork-like briquettes that slow-release methoprene, an insect growth inhibitor. Some sites required multiple visits. “When we first put the briquettes in some pools, there was so much fire debris, the briquettes were having trouble releasing the methoprene,” said Sequeira. In some instances, the cyclone fencing many contractors installed around pools for safety presented access challenges and the district is now considering integrating drones into surveillance programs to help overcome similar challenges in the future.

Now, almost two years later, there are only 37 sites each in Kenwood and Glen Ellen being monitored by the district. In the midst of rebuilding, sites are being taken off the list regularly as homeowners begin to use and monitor their properties again. The district is still treating a total of 400 pools in the burned areas.

However, vector control is anything but idle.

“Mosquito season started off fast and furious this year,” said Sequeira, “in part due to heavier rainfall, causing more overgrowth to obscure containers and other sources of water mosquitoes can use for breeding.”

In Kenwood, Glen Ellen and Sonoma, most calls generally come early in the season, said Sequeira, because that’s when the Western tree hole mosquito emerges and lays her eggs. The tree hole mosquito lays eggs in the water contained in rot-holes of trees, such as oak, laurel and madrone, but will occasionally breed in artificial containers such as roof gutters, tires, cans and buckets. The tree hole mosquito is also the transmitter of Canine heartworm. Like all species of mosquitoes, only the female bites and sucks blood.

Requests for district control and prevention services for all types of vectors are up 24 percent this year, but mosquito service requests, compared to the same time last year are up 54 percent, said Sequeira.

That jump might mean more pest activity this year – the district says climate changes are increasing mosquito and tick habitat and causing seasonal population shifts – but it can also be attributed to people’s increased awareness of the district’s services, which are all free. Funded by taxpayer money, the district offers free inspections and control services, which run the gamut from natural to chemical-based, with an emphasis on prevention. One of the district’s popular non-chemical alternatives, in the case of mosquitoes, is a delivery of live mosquitofish to ponds and other permanent water features. The favorite snack of mosquito fish? Mosquito larvae.

As a last resort, the district does use “fogging,” a mass spraying of a large area, like in the west county redwoods or southern Sonoma Valley wetlands. Neighbors are notified and sprays are tracked on their website at www.msmosquito.com/resources. Links to the variety of products the district uses can also be found there. Residents can request free services online or call the district at 285-2200 with questions or concerns.

“I continue to be a little concerned about the fire recovery and especially the pools that are still surviving, and often the pools are on the properties that are the most challenging to rebuild on, so anything we can do to help, let us know,” First District Supervisor Susan Gorin told Smith at the meeting. “Anything we can do to let them know this is their responsibility.”


Sarah Phelps is an editor and reporter. She was raised in Kenwood and has a BA from Loyola Marymount University.
Email: sarah@kenwoodpress.com

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