City of Thornton

The City of Thornton’s Mosquito Management Program

The City of Thornton Mosquito Management Program completed its 23rd year of cost effective biorational integrated mosquito management operations in 2010 with Colorado Mosquito Control as its contractor. Mosquitoes are dynamic insects which are capable of rapid population increases dependent on habitat, water level, rainfall events, and temperature patterns. The experience and knowledge possessed by CMC employees for the local land and irrigation patterns enables an overall reduction of mosquitoes. The biorational management operations and data driven response to spikes in mosquito abundance are aimed at reducing the risk and annoyances associated with mosquitoes. If left unmanaged residents residing throughout large sections of the city would be burdened by mosquitoes, thereby resulting in a decreased quality of life and reduced ability to enjoy outdoor activities.

The objective for the City of Thornton Mosquito Management Program is to utilize trained CMC field biologists to suppress the number of mosquitoes, in the aquatic larval habitats. This reduces the potential for mosquitoes to emerge from the water to feed on and reduce the transmission of vector borne diseases to the residents of Thornton. In the City of Thornton CMC monitors adult mosquito populations via a surveillance trapping network to enable a proactive response to suppress West Nile Virus vector mosquito populations prior to a public health emergency outbreak. Adult mosquito population data provides real time information regarding the nuisance and risks associated with mosquito populations in Thornton. Trapping data provides a scientific basis when determining the need to reduce the mosquito populations via adult mosquito control materials. CMC sets 10 mosquito surveillance traps in the City of Thornton on a weekly basis to monitor the mosquito counts within city.
This objective enables a decline in the overall mosquito populations, while reducing the threat of mosquito borne disease transmission, at the least possible cost, and with the least possible impact on the people and natural environment. CMC will continue to strive and demonstrate a commitment to Integrated Pest Management principles for a progressive approach to mosquito reduction.

Service Area
The larval control area for the City of Thornton is defined by the city limits of Thornton. Although many of the mosquito production sites are outside the city limits, all are well within the flight range of most mosquitoes. Larval control work outside the city will continue to remain a critical part of the overall operations of CMC and is accomplished with a separate but cooperative program with Adams County and neighboring communities.

Studies have indicated that adult mosquitoes can travel several miles in search of a blood meal and new habitats for offspring. Mosquitoes can be attracted from outside city limits into a more favorable environment inside city limits by factors including carbon dioxide, protection from wind, a nutrient rich larval site and harborage from heat. Mosquito reduction by Colorado Mosquito Control across the cities within Larimer and Weld Counties greatly reduces transient mosquito populations, thereby protecting the public from West Nile Virus transmission and the nuisance associated with mosquitoes.

The Story behind the Mosquito Management Program
Thornton’s Integrated Mosquito Management program focuses primarily on utilizing naturally occurring soil bacteria (Bti) larvicides, to control mosquitoes in the larval stage, instead of relying entirely on application of pesticides in the form of fogging materials. The program primarily utilizes applications of Bti, a stomach toxin, which is target-specific to larval mosquitoes. This naturally occurring bacteria is activated by a specific pH within the larval gut and disrupts the larvae’s ability to consume and digest food resources.
When applied by trained applicators, IPM programs return beneficial results in reduced pesticide use, reduced frequency of pesticide resistance, and reduced exposure to pesticides by the environment. The Mosquito Management Program offered by CMC follows successful IPM principles for cost effective, scientific methods of survey/inspection, evaluation, diagnosis, application and record keeping of materials used.


Surveillance Trapping Operations
Data on mosquito abundance and species identity is critical in the operation of a successful mosquito management program. Over the past few years, identifying, packaging, and sending Culex mosquito pool samples to the Colorado Department of Health and Environment (CDPHE) Lab for West Nile Virus testing has also become critically important in the battle against West Nile Virus and other mosquito-borne diseases. The purpose of a surveillance program is to be an early warning system. In other words, the system is intended to alert mosquito personnel of an impending health crisis. The key is that the system gives advance warning that mosquito control personnel can work with County Health Departments and city officials to take effective steps in minimizing the number of human cases.
In 2010, Colorado Mosquito Control monitored a statewide network of over 250 trap sites, with over 3,200 trap nights set, collecting more than 425,000 adult mosquitoes that were counted and identified to species by the CMC Surveillance Laboratory. While individual traps provide only limited information, trap data is interpreted in the context of historical records for the same surveillance location, going back in time more than a decade in some locations. Individual traps are also compared to other traps from around the region that were set on the same night and therefore exposed to similar weather conditions.

CMC employs the CDC dry-ice baited light traps to monitor mosquito populations. The CDC light trap uses carbon-dioxide from dry ice as bait to attract female mosquitoes seeking a blood meal from a respiring animal. Once attracted by the CO2, the mosquitoes are lured by a small light to a fan that pulls them into a net for collection.

Targeted Ultra-low Volume Adult Mosquito Control
Adult mosquitoes can come from unknown unidentified sites or may migrate in from uncontrolled areas. Thornton uses all available data from CDC light traps, Mosquito Hotline annoyance calls, and field technician reports to focus adult mosquito control efforts on specific, very limited “targeted” areas. In parts of the community were high numbers of mosquito annoyance calls are received, “floater” CDC light traps are set to evaluate adult population levels and species make-up. In most cases, a direct correlation is evident between areas with high complaint calls and high trap counts. While this correlation allows us to focus adult control in these areas, the emphasis is placed on finding the source of breeding and continued larval control measures.

Over 95% of the Thornton’s Mosquito Control Program is targeted against larval (aquatic stage) mosquitoes utilizing biological control materials. However, on occasion adult mosquito spraying becomes necessary. At that point Colorado Mosquito Control utilizes 3.3% Permethrin in ultra low volume (ULV) spray applications via truck-mounted fogging machines. ULV sprayers dispense an extremely small amount (0.0035 pounds per acre) of fine aerosol droplets which stay aloft and kill adult mosquitoes on contact.

Permethrin is a synthetic pyrethroid similar to the insecticide pyrethrum which occurs naturally in chrysanthemum plants. Permethrin is found in a variety of products, including household insecticides, flea dips, repellents for clothing, sprays for pets, and lice shampoos. This pesticide has been selected to achieve effective control of mosquitoes and suppression of West Nile Virus transmission with the least impact on human health and the environment.

Fogging applications are performed based on mosquito populations caught in traps on a nightly basis. The city is divided into zones. Specific neighborhoods are fogged when surveillance traps catch 100 floodwater mosquitoes, referred to as a “Nuisance Threshold” The thresholds for fogging applications are established by an industry standard that measures vector and nuisance mosquito populations.

Colorado Mosquito Control uses state of the art technology, correct application timing, and least-toxic products to minimize non-target impacts. All adult mosquito control is accomplished using calibrated Ultra Low Volume (ULV) equipment and performed after dusk. This type of equipment produces droplets averaging 12 microns in diameter and allows for a minimal amount of product to be put into the environment. These treatments take place in the evening when mosquitoes are flying in greater numbers and non-target activity is greatly reduced. Using this application technique, the overall goal of minimal environmental impact and effective adult control is achieved in the targeted area. All insecticides used by Colorado Mosquito Control are registered by the EPA and the Colorado State Department of Agriculture. For additional information regarding permethrin, including toxicology data please visit: and click on the tab for pesticides.