By Amy Silverman
By Olivia LaVecchia
By Monica Alonzo and Stephen Lemons
By Chris Parker
By Michael Lacey
By Weston Phippen
Tempe conducted numerous pesticide applications to control mosquitoes, as well as midge flies, in and around Town Lake and in the Salt River bed.
Between September 2 and 14, the city applied bacterial larvicides -- Vectobac and Vectolex -- directly into the lake and shallow pools both above and below the lake. The larvicides were spread at a concentration of 20 pounds per acre.
In October, the city switched to the larvicide Abate, which was applied at five pounds per acre to the lake and nearby shallow pools. The larvicide treatments cost the city approximately $68,000, city records indicate.
While the larvicides are effective in killing the insects before they become capable of flying, a different insecticide was employed to kill airborne mosquitoes.
Between September 2 and November 5 -- the day before the Town Lake dedication -- the city used pickup trucks to apply a fogging compound containing the pesticide Anvil. The pesticide was applied on 12 separate dates, including the four days leading up to the dedication.
City officials say the fogging applications cost $2.76 an acre. The city treated 500 acres of river bottom and Town Lake between the Hohokam Expressway and McClintock Drive 12 times since September, at a cost of about $16,560.
While city and county officials say malathion and Anvil are safe, environmental organizations have warned of potential dangers.
Malathion, an organophosphate insecticide, works by interfering with the central nervous system in insects -- and potentially humans. Although it is considered one of the less acutely poisonous of this family of pesticides, exposure to malathion can cause respiratory distress, headache, dizziness and nausea, according to a 1999 study by the U.S. Environmental Protection Agency.
Anvil's primary active ingredient is sumithrin, which is a synthetic pyrethroid insecticide generally considered to be less toxic than organophosphates. There are some indications that pyrethroids as a class may interfere with the immune and endocrine systems.
The use of malathion as a general treatment for encephalitis-carrying mosquitoes came under fire recently in New York, where mosquitoes were linked to the West Nile virus, which caused several deaths.
"Controlling Culexpopulations with . . . malathion is a strategy of last resort, when all other control possibilities have been exhausted and a public health emergency requires action," the New York Public Interest Research Group said on September 30. "It should not be the first or only line of defense."