In the summer months, mosquitoes are active. These common flying insects can carry diseases like West Nile virus and St Louis encephalitis, which can be very serious.
Mosquitoes breed in pools of standing water and in containers that hold standing water, such as tires and buckets. To help avoid mosquito-transmitted diseases, mosquito populations can be reduced by killing their larvae with chemicals or oils placed in the water. When adult mosquito numbers are very high and the risk of spreading disease is increased, pesticides are sprayed from airplanes over large areas of cities. The July 17, 2013, issue of JAMA includes 2 articles on West Nile virus.
One of the most frequently used chemicals for aerial spraying is called Duet. It has 3 active ingredients.
Prallethrin is in the class of chemicals called pyrethroids. These chemicals are similar to natural ones found in chrysanthemum flowers that keep insects away from the flowers. These chemicals kill insects by interfering with electrical signals in nerves.
Sumithrin is also a pyrethroid that is commonly used to control head lice in people.
Piperonyl butoxide blocks an enzyme that breaks down pyrethroids in insects, making the chemicals more effective.
Other chemicals used in aerial spraying include organophosphates like malathion. These agents block an enzyme that breaks down a chemical called acetylcholine, which is responsible for nerve signaling. Too much of that chemical interferes with nerve signals in mosquitoes, killing them.
Insecticide sprays for mosquito control are applied using a technique called ultra-low-volume spraying. About 3 oz of chemical are released per acre of land. These sprays work by creating a mist that drifts through the air and contacts flying mosquitoes while they are active. The spraying occurs at night, when most people are indoors. The prallethrin in Duet excites mosquitoes, causing them to become more active and fly into the spray containing the sumithrin and prallethrin droplets that kill them on contact.
The chemicals used in these sprays are broken down by light and soil, usually within hours of being sprayed. The droplets of spray have enough insecticide to kill mosquitoes but not enough to cause appreciable harm to the environment or to affect human health. Humans and most animals have enzymes that break down the chemicals used in these sprays. Even if humans have some exposure to the chemicals, they are relatively safe because of these enzymes.
Studies of humans in spray zones show no evidence of insecticide exposure. Spraying has been shown to reduce transmission of diseases from mosquitoes. Because some of these diseases, like West Nile virus, can be very serious, the very small risk of being in a spray area is outweighed by the benefits of significantly lowering the risk of serious disease from mosquitoes.
Centers for Disease Control and Preventionwww.cdc.gov/ncidod/dvbid/westnile/qa/pesticides.htm
Environmental Protection Agencywww.epa.gov/pesticides
To find this and previous JAMA Patient Pages, go to the Patient Page link on JAMA’s website at www.jama.com. Many are available in English and Spanish. Patient Pages on West Nile virus were published on July 23, 2003, and September 12, 2012.
Sources: Macedo PA, et al. J Am Mosq Control Assoc. 2010;26(1):57-66Carney RM, et al. Emerg Infect Dis. 2008;14(5):747-754
Livingston EH. Safety of Aerial Pesticide Spraying for Mosquitoes. JAMA. 2013;310(3):333. doi:10.1001/jama.2013.8275