As part of our urban entomology program we measure the efficacy of treatments for Argentine ant infestations around homes in California. Since many common insecticides used against ants are appearing in urban waterways in California and in other states, we decided to do concurrent measurement of insecticide runoff resulting from these treatments. Of particular concern are pyrethroids and fipronil, the most common products used against the ants. Driveways are the most obvious paths to the street and drains that lead to urban waterways. We devised water dams to collect water running down driveways, normally due to irrigation or rain. We initially found significant amounts of both fipronil and pyrethroids in the runoff to the street. Reducing the fipronil driveway bandwidth to a pin stream reduced its runoff. Significant additional reductions were made by having a 1 ft buffer of the fipronil from the driveway. Reducing runoff of pyrethroids down the driveway has proven to be more difficult. Bifenthrin granules, carefully applied away from the driveway, show much lower runoff of the active ingredients down the driveway than sprays. Even when pyrethroids are not sprayed within two feet of the driveway, as specified by new product labels, significant amounts run off. We have shown that most of the pyrethroid runoff is occurring as particles in the runoff rather than the liquid phase. This fact may explain why buffer zones are less effective with pyrethroids than fipronil. Dust and soil particles containing pyrethroids can easily reach the driveway due to wind or other disturbances.

Insecticide runoff from homes treated for ant infestations

248th National Meeting (2014)

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