Malathion

Malathion is an organophosphate insecticide which acts as an acetylcholinesterase inhibitor. In the USSR, it was known as carbophos, in New Zealand and Australia as maldison and in South Africa as mercaptothion.
Pesticide use.
Malathion is a pesticide that is widely used in agriculture, residential landscaping, public recreation areas, and in public health pest control programs such as mosquito eradication. In the US, it is the most commonly used organophosphate insecticide.
A malathion mixture with corn syrup was used in the 1980s in Australia and California to combat the Mediterranean fruit fly. In Canada and the US starting in the early 2000s, malathion was sprayed in many cities to combat west Nile virus. Malathion was used over the last couple of decades on a regular basis during summer months to kill mosquitoes, but homeowners were allowed to exempt their properties if they chose. Today, Winnipeg is the only major city in Canada with an ongoing malathion adult-mosquito-control program.
Mechanism of action.
Malathion is an acetylcholinesterase inhibitor, a diverse family of chemicals. Upon uptake into the target organism, it binds irreversibly to the serine residue in the active catalytic site of the cholinesterase enzyme. The resultant phosphoester group is strongly bound to the cholinesterase, and irreversibly deactivates the enzyme which leads to rapid build-up of acetylcholine at the synapse.
Production method.
Malathion is produced by the addition of dimethyl dithiophosphoric acid to diethyl maleate or diethyl fumarate. The compound is chiral but is used as a racemate.
Medical use.
Malathion in low doses (0.5% preparations) is used as a treatment for:
Preparations include Derbac-M, Prioderm, Quellada-M and Ovide.
Safety.
General.
Malathion is of low toxicity. Its metabolite malaoxon is 61x more toxic, being a more potent inhibitor of acetylcholinesterase. 
According to the United States Environmental Protection Agency, no reliable information is available on adverse health effects of chronic exposure. 
In 1981, B. T. Collins, director of the California Conservation Corps, publicly swallowed a mouthful of dilute malathion solution to demonstrate its safety following an outbreak of Mediterranean fruit flies in California. Malathion was sprayed over a area to control the flies.
Carcinogenicity.
Malathion is classified by the IARC as probable carcinogen (group 2A). Malathion is classified by US EPA as having "suggestive evidence of carcinogenicity". This classification was based on the occurrence of liver tumors at excessive doses in mice and female rats and the presence of rare oral and nasal tumors in rats that occurred following exposure to very large doses. Exposure to organophosphates is associated with non-Hodgkin's lymphoma. Malathion used as a fumigant was not associated with increased cancer risk. Between 1993 and 1997, as part of the Agricultural Health Study, no clear association between malathion exposure and cancer was reported.
Amphibians.
Malathion is toxic to leopard frog tadpoles.