The Environmental Protection Agency (EPA) evaluates and registers (licenses) pesticides to ensure that they can be used safely. These pesticides include products used in the mosquito control programs established by states and communities. To evaluate any pesticide, EPA assesses a wide variety of tests to determine whether a pesticide has the potential to cause adverse effects on humans, wildlife, fish and plants, including endangered species and non-target organisms.
Officials responsible for mosquito control programs make decisions to use pesticides based on either an evaluation of the risks to the general public from diseases transmitted by mosquitoes, or on an evaluation of the nuisance level that communities can tolerate from a mosquito infestation.
Mosquito control officials select specific pesticides and other control measures that best suit local conditions in order to achieve effective control of mosquitoes with the least impact on human health and the environment.
Based on these criteria, Boulder County Public Health has determined Permethrin to be the appropriate mosquito control product for use in Boulder County.
Permethrin, a man-made version of Pyrethrin which is derived from plants in the Chrysanthemum family, is used as a last resort, and only when nuisance threshold values have been exceeded.
Nuisance threshold values (mosquito numbers above 100 per trap) are determined by trapping adult mosquitoes in annoyance areas. Permethrin is applied using a method known as ultra-low volume spray (droplet size calibrated to 12-20 microns) so that an extremely small amount of product is applied over a large area (at less than 0.007 lbs/acre ~1 oz/acre).