If it seems like aerial bombardments of mosquitoes are coming fast and furious this summer, rest assured it's not a product of the imagination.
Mosquito control district aircraft are taking to the skies earlier and more frequently this season than in any other year since the West Nile virus was detected in the Sacramento region in 1999.
The stepped-up aerial pesticide sprayings are an unintended consequence of a federal court ruling that forces ground pesticide use by mosquito control districts to fall under the permit requirements of the federal Clean Water Act.
Specifically, mosquito district officials say, meeting the Clean Water Act requirements for groundwater treatments means more paperwork and administrative duties for ground technicians treating larval pools. The new rules have caused technicians to reach an average of 50 fewer larval pools monthly than they would have before the regulations went into effect this year, according to district officials.
Since aerial spraying of adulticides doesn't face the same restrictions as ground treatments near water, the district has opted to go after adult mosquitoes with sprayings by air or truck-mounted sprayers.
That, in turn, leads to another unintended consequence of the new Clean Water Act rules: Airborne pesticides may drift over broader geographical areas. Not to mention, say mosquito control district officials, an increased likelihood that West Nile virus may spread to humans in a big way this season.
"The risk that a public health crisis could emerge from these permit requirements is very real," Catherine Smith, executive director of the Mosquito and Vector Control Association of California, said in a June 27 letter to state officials.
Specifically, the new permit requirements mean ground technicians have to perform a check the day before treating water with larvicide, the day of and several days afterward – essentially replacing one step with three.
"Anything that inhibits our ability to control larvae and allows adult mosquitoes to grow wings and fly means we're more likely to take to the air to control them," said David Brown, head of the Sacramento-Yolo Vector and Mosquito Control District. "It certainly plays into the problem."
West Nile virus has been a growing concern in the Sacramento region since 2004, when the area became ground zero in California for risk of infection.
The potentially fatal virus, spread by mosquitoes, causes symptoms that appear two to 12 days after exposure, including fever, body aches, headaches and swollen lymph glands. Most people recover but the virus can cause partial paralysis or swelling of the brain. As yet this year, no human cases have been confirmed in the region.
This year, however, more dead birds and mosquitoes are testing positive for the virus earlier in the season than in years past, Brown said, with the first avian specimen logged on Jan. 19.
Already, in Sacramento County, district aircraft have sprayed 100,000 acres with adulticide on four separate days. Last year, there was only one aerial spraying, of 33,000 acres in late August. And in 2010, the entire mosquito season saw just two aerial treatments, covering about 70,000 acres in July.
By May of this year, the Sacramento-Yolo district had announced it was in "emergency planning mode." As the season progresses and temperatures get hotter, "We know West Nile virus will be on the rise," Brown said.
Meanwhile, groups concerned about the spread of pesticides say mosquito control districts are using scare tactics to nudge state officials into watering down their permit requirements for ground treatments.
"Mosquito districts just need to fill out a few simple permit requirements to track pesticide use in or near waterways,"said Asael Sala, a community organizer in south Sacramento for Pesticide Watch. "Yet they'd rather resort to strong-arm tactics to get what they want, like issuing threats of more aerial spraying."
Indeed, input from mosquito control districts has already persuaded the State Water Resources Control Board to adopt several changes to the permitting process.
"Anytime an entity comes to us with a concern, we definitely make a point of meeting with them to understand their issues," said George Kostyrko, chief information officer of the State Water Resources Board.
Mosquito control districts argue that the restrictions on ground treatments will simply result in more toxic forms of pesticide pollution as the drift from large-scale aerial or truck spraying may reach sensitive waters in California.
"An acute illustration is Lake Tahoe," Smith said in her letter. "Increased paperwork and delayed treatment times could double the amount of pesticides used in and around Lake Tahoe."
Mosquito control districts are pursuing a solution in Congress as well, pushing a House bill that would exempt them from Clean Water Act requirements. The bill, HR 872, passed the House but is being held up in the Senate by Sen. Barbara Boxer, D-Calif., who objects to its weakening of environmental protections.
In south Sacramento, which has been the target of all four aerial sprayings so far this season, some residents say notification and outreach efforts to engage the community in prevention have been lacking this year.
"They don't even bother to encourage us to work together as a community to get rid of standing water," said Lanae Davis, a librarian at Fruit Ridge Elementary School and a caretaker of its lush organic garden.
Davis said she signed up on the www.fightthebite.net website to get advance notice of the sprayings. She noted that, from her experience working with kids at school, it's clear not everyone in south Sacramento has access to a home computer and the Internet.
Just after 8 o'clock one recent evening, while children rode bikes nearby, Davis said, she was covering tomatoes and berries with plastic tarps when she saw a plane flying at an elevation of 300 feet toward the school. She said she ran inside and watched as the aircraft passed over the schoolgrounds three times, leaving fine mists in its wake.
"What I saw was a slight residue," Davis said. "There were teeny tiny droplets on the tarps, and even when they were totally gone, there's still a residue left."
Spraying adulticides means using stronger chemicals such as organophosphates that are linked by research to health risks in cumulative doses but certified as safe by the Environmental Protection Agency.
For the hazards they present, such as potential neurological or respiratory damage, adulticide treatments are not nearly as effective as on-the-ground eradication of mosquito larvae, said Sala of Pesticide Watch. Aerial spraying kills only about 40 percent of the adult population, he said, with success depending on the pesticide falling directly on mosquitoes in flight.
"Usually in 10 days the mosquitoes rebound and they have to spray again," Sala said.
Engaged in the bigger battle to keep humans safe from West Nile virus, officials see chemicals as beneficial to public health. That's one reason they are so opposed to falling under the umbrella of the Clean Water Act.
The pesticides used by the mosquito control districts were first subject to the Clean Water Act permit requirements this year, following a ruling by the 6th U.S. Circuit Court of Appeals that the chemicals should be considered potentially harmful to waterways.
Said Brown, ruefully, "Over 30 to 40 years of our operations, we've never been classified as pollutants."