The Sacramento-Yolo Mosquito and Vector Control District plans to spray 23,000 acres in two areas of south Sacramento for three consecutive nights starting tonight in an effort to control the spread of West Nile virus.
Here are questions -- and the answers -- about the effort gathered from experts on the topic.
Q: Where and when will spraying be done?
A: If conditions allow, planes will spray sometime between 8 p.m. and midnight each night. The Florin/Elk Grove and Pocket areas targeted for spraying are at high risk of West Nile virus transmission. The district so far has no plans to spray elsewhere.
The district may postpone or cancel the spraying if weather or other causes make conditions ineffective.
Q: Why spray rather than use other methods?
A: Spraying is most effective for killing adult mosquitoes. Other methods, such as eliminating the standing water in which mosquitoes breed or placing mosquitofish in water, are no longer effective once the mosquito can fly.
When the district finds infected adult mosquitoes, it first spot-sprays insecticide on the affected area. In south Sacramento, spot treatments did not eliminate the infected mosquito population. So the district decided on aerial treatments.
Q: Why spray when no human cases have been reported yet?
A: There is a delay between the time a person is infected by West Nile virus and the time the infection is reported to health authorities. This delay can be as much as four weeks.
Waiting until human cases are reported would allow more opportunity for the virus to be transmitted and would not effectively protect public health.
Q: Who pays for the spraying, and how much does it cost?
A: The district, which is funded through property taxes, pays. The aerial application costs less than $2 per acre.
Q: What is the insecticide, and how does it work?
A: EverGreen Crop Protection EC 60-6 contains two active ingredients, pyrethrins and piperonyl butoxide (PBO).
Pyrethrins, a group of natural insecticides derived from chrysanthemum flowers, attack a mosquito's nervous system and paralyze the insect.
PBO is a less toxic agent and acts as an insecticide synergist: It blocks the mosquito's ability to degrade pyrethrins. This makes the pyrethrins more effective and enables use of a smaller amount of the insecticide.
Q: Who regulates this insecticide?
A: The U.S. Environmental Protection Agency registers insecticides nationally, and the California Department of Pesticide Regulation approves use in the state. These two agencies also must approve any specific application methods, such as aerial treatments.
Q: Is Crop Protection EC 60-6 safe?
A: No insecticides are "safe" in high doses -- but the treatment concentrations are less than 0.000015 ounces per square foot.
The health effects of high doses of the active ingredients are not well-documented in humans but are thought to be mostly skin and respiratory irritants.
In the long term, pyrethrins are considered to be possible cancer-causing agents at high doses, but studies are lacking. There are no long-term effects of PBO on animal development or reproduction, but studies of carcinogenicity in humans are absent.
In mosquito spraying, concentrations of insecticide are very low, and targeted toward small insects. Human skin is resistant to absorbing the insecticide, and what does get into the human body is quickly detoxified -- people can break down the chemicals much more quickly than insects can.
Q: What happens long-term to the active ingredients in the insecticide in the environment?
A: Pyrethrins decompose when exposed to sunlight, air and water. Spraying is done at night so that chemicals are likely to break down by the next morning.
PBO also degrades readily in the environment. Both ingredients disappear in a matter of weeks.
Q: Does the insecticide harm other beneficial insects, or plants, animals and humans?
A: The insecticide is intended to harm insects, so even beneficial insects such as honeybees can be affected.
However, the doses applied are very low and aim to minimize harm to insects and animals larger than mosquitoes.
The aerial spraying will also occur at night, when insects such as bees are not outside.
Pyrethrins are very toxic to fish and water-dwelling insects. Toxicity is low in humans, other mammals and birds.
The insecticide is not harmful to plants since it works on the nervous system.
Q: Are there people who should take special precautions during the spraying?
A: People who have allergies and asthma should stay indoors as a precautionary measure. Health officials do not recommend other special precautions. To see more of The Sacramento Bee, or to subscribe to the newspaper, go to http://www.sacbee.com/. Copyright (c) 2008, The Sacramento Bee, Calif. Distributed by McClatchy-Tribune Information Services. For reprints, email tmsreprints@permissionsgroup.com, call 800-374-7985 or 847-635-6550, send a fax to 847-635-6968, or write to The Permissions Group Inc., 1247 Milwaukee Ave., Suite 303, Glenview, IL 60025, USA.
Copyright (C) 2008 The Sacramento Bee, Calif.