Winter rain, spring heat bring a heavy mosquito season to the North Bay

The North Bay is experiencing a heavier and earlier mosquito season this year, thanks to major winter rains and warmer spring temperatures.

The atmospheric rivers that passed through the region earlier this year resulted in large areas of stagnant water, providing the perfect environment for adult mosquitoes to flourish with the recent heat spikes, according to the Marin/Sonoma Mosquito & Vector Control District.

The district has experienced a 119% increase in calls for service compared to this time last year - with one recent day registering almost 200 calls within the two counties, spokeswoman Nizza Sequeira said. The agency typically fields about 5,000 service calls a year on a range of pests from mosquitoes to yellow jackets to rodents.

The last time there was as large a call volume for the district was in 2016. The high season typically runs from mid-spring through October, Sequeira said.

She said the district saw an increase in calls about two weeks ago when the weather started warming up.

The rise in mosquitoes has forced local residents to break out the citronella candles and bug spray and turn to other tough measures to combat the pest.

In Sonoma Valley, Mission Ace Hardware & Lumber saw within the past month an uptick in customers coming in for mosquito foggers, repellent wristbands and other products to rid themselves of the insects, manager Rob Yovino said.

“It was a dramatic increase over last year,” Yovino said about the number of customers.

Sonoma and Marin counties combined have 23 species of mosquitoes.

The Mosquito & Vector Control District has 18 technicians who attempt to keep tabs on about 20,000 known mosquito sources in the two counties that they check regularly, in addition to responding to specific service calls, Sequeira said.

“The hardest part is that we don’t know what is happening in peoples’ backyards,” she said.

Technicians look to remove standing water around a property. Any item that can hold water for 72 hours can be a breeding ground. Problem spots typically found in backyards include: rain barrels that are not covered; pool and spa areas with standing water on top of the covers; clogged rain gutters; and stopped-up potted plant saucers.

“It’s exactly like detective work,” Sequeira said.

If mosquitoes remain, the district can take more thorough steps such as providing mosquitofish that can eat larvae in ponds or other small bodies of water.

At the request of the property owner, technicians also can spray a foglike insecticide if it is warranted. The sprays are typically pyrethrins - a group of natural compounds extracted from chrysanthemum flower - or etofenprox, a low-toxicity synthetic version of pyrethrins.

The district provides the mosquito control services for free, and the waiting time is about two weeks.

Outside of the nuisance of bites and spoiled outdoor barbecues, mosquitoes can threaten public health, transmitting diseases such as West Nile virus, dog heartworm and western equine encephalomyelitis.

The district monitors those health threats via mosquito traps. It had not detected mosquitoes carrying West Nile as of last week, Sequeira said.

However, some trees within the area have been breeding grounds for those carrying the dog heartworm. Those mosquitoes have been able thrive within the rot of oak trees, Sequeira said. Cats and other mammals also can be susceptible to the infection.

For those wanting to learn more about the district’s efforts, the agency is having an open house from 11 a.m. to 3 p.m. Saturday at its headquarters, 595 Helman Lane in Cotati.