Daily News Archive

Mosquito Sprays Unsuccessful in California
(Beyond Pesticides, August 11, 2004)
A recent bout of pesticide fogging for West Nile Virus (WNV) in Los Angeles County, California has been ineffective in reducing adult mosquito populations, according to the Pasadena Star.

On the night of Wednesday, August 4, workers from the Greater Los Angeles County Vector Control District used pickup trucks to spray an area along two riverbeds, where WNV-infected mosquitoes and birds had been found, according to the District. Resmethrin, a synthetic pyrethroid designed to kill adult mosquitoes, was sprayed through parts of the towns of Whittier, Pico Rivera, Santa Fe Springs, Montebello and Whittier Narrows.

Officials had expected the pesticide would kill about 70 percent of adult mosquitoes in the area, but this did not happen. According to Minoo Madon, scientific technical services director at the Vector Control District headquarters in Santa Fe Springs, before and after monitoring revealed that the pesticide did not kill 70 percent of mosquitoes. Madon would not disclose the actual percentage killed, but said, “Let’s just say the results were not satisfactory.” Madon suggested that a stiff breeze might have prevented the spray from actually reaching the mosquitoes.

The spraying was conducted in an effort to control the spread of WNV. So far this year, 102 people in California have been diagnosed with West Nile virus, the second highest count in the country, and two deaths have been attributed to the disease, one in Los Angeles County. WNV human case reports do not include the roughly 80 percent of infected persons who show no symptoms (according to the Centers for Disease Control and Prevention) and can include mild as cold or flu-like symptoms or more serious neuroinvasive symptoms. The relatively recent spread of West Nile to California has led to widespread concern and a number of communities have sprayed adulticides in an attempt to control mosquitoes.

However, the spraying of pesticides is not always the answer to mosquitoes or WNV. Adulticides are often ineffective, as demonstrated by the spraying in Los Angeles County. Even under ideal conditions only a small amount of these pesticides ever reaches the target pests, they do little to restrict breeding in adult mosquitoes, and mosquitoes can become resistant to them, on top of dangers to humans and the environment.

With the growing concern over WNV, it is important for local governments to provide accurate public education and safe, long-term solutions rather than simply spraying neighborhoods with dangerous pesticides. More effective mosquito management techniques include increased public education, breeding ground elimination, personal protection, and the use of larvicides to kill mosquito larvae before they become biting adults. The use of adulticides like resmethrin should be avoided in most circumstances. Pyrethroid exposure can lead to a variety of health effects including headache, nausea, incoordination, convulsions, swelling, burning, and death due to respiratory failure. Infants are particularly at risk because their bodies can’t efficiently break down pyrethroids. Pyrethroids have also been linked to endocrine disruption, cancer, and are extremely toxic to aquatic organisms.

TAKE ACTION: Fight to prevent unnecessary adulticiding in your community and promote effective, intelligent mosquito management. For help see Beyond Pesticides Tools for Activists page. For more information on West Nile Virus and mosquito management see a new factsheet by Beyond Pesticides: The Truth About Mosquitoes, Pesticides, and West Nile Virus.