What's in Mosquito Fog? This and More Gets Answered by an Expert

We're all familiar with the alerts for mosquito fogging, but how much do we really know about the process?

Patch decided to ask an expert to help us answer some questions from residents about what chemicals are used and how it helps control the mosquito population. We talked with Paul Geery at the Desplaines Valley Mosquito Abatement District who has 33 years of experience controlling these pesky bugs to find out.

Many of these questions come from residents, but if you've got a follow up question, ask it in comments and we'll see if we can get you the answers you're looking for.

La Grange Patch: Can you introduce yourself and tell us what the Desplaines Valley Mosquito Abatement District does?

Paul Geery: My name is Paul Geery. I’m the Assistant Manager and Biologist for the Desplaines Valley Mosquito Abatement District. This is my 33rd mosquito season. The District was formed in 1927 and encompasses 77 square miles in western Cook County containing five townships and 31 villages. The goal of the district is to reduce mosquito annoyance and reduce potential disease transmission by mosquitoes using the safest and most environmentally sound methods available. Much more could be said and more information is available on our web site at: www.desplainesvalleymad.com.

Patch: Can you tell us why you use a fogger and how it helps combat mosquitoes?

Geery: It is important to realize that adult mosquito control or “fogging” is a very small part of what we do and is considered supplemental. Over 98 percent of what we do is involved in mosquito larval control and support efforts such as surveillance, equipment maintenance, etc.

Mosquitoes are easiest to kill in the larval stage when they are trapped in water. Once they are adults it becomes much more difficult to kill them, given their great mobility. Unfortunately, the group of mosquito species that can transmit West Nile Virus (WNV) can develop in any water that exists for at least 7-10 days. We can and do treat many of the potential sources for mosquito development throughout the district, such as street catch basins, off-road catch basins, open water sources such as ditches, floodplains, retention ponds, artificial containers like tires or dumpsters, etc.

However, many sources can exist that we are not able to control. Every gutter that is plugged and holds water is a potential source for mosquito development. Backyard swimming pools that are not maintained, kiddie pools that are not dumped at least once a week, birdbaths, upright wheel barrels that hold water and many other small sources of standing water are dispersed throughout the area. As a result there will always be some adult mosquitoes.

The district only uses “fogging” (adult mosquito control) when the level of WNV in the mosquito population is high and the potential for human disease is significant. We do not use adult mosquito control for nuisance species for a variety of reasons. Adult mosquito control is the least effective of the mosquito control tools at our disposal, but it is the only tool available against adult mosquitoes. Currently, the level of WNV in the adult mosquito population is very high. In addition, human cases of WNV are being confirmed daily.

Patch: Can you tell us what chemicals are used and how much is used when doing the fogging treatment?

Geery: The process used is called ULV, or ultra low volume. The application rate is only .003 pounds of active ingredient per acre, thus “ultra low volume”. The pesticide used is called Anvil10+10, which is diluted with a light mineral oil. The active ingredients are Sumithrin, a synthetic pyrethroid, and a synergist Piperonyl Butoxide.

Patch: Are these dangerous chemicals? 

Geery: The United States Environmental Protection Agency regulates and registers all pesticides used in the United States. Only pesticides that meet their requirements for safety to humans and the environment are allowed to be used. The label requirements and application rates are set with a very large margin of safety to prevent significant impact on both humans and the environment.

Patch: Will the chemicals harm cars parked in driveways, animals that are outside when the truck passes, or people's lawns?

Geery: The pesticide used for adult mosquito control, at the amounts used, should not cause harm of any kind. It dissipates very quickly and breaks down within a short time, especially in sunlight. Again, the U.S. EPA regulates the use of pesticides to prevent such harm.

Patch: Why are residents alerted when fogging will occur? Is it to keep them inside on those nights?

Geery: People like to know what is happening around them, so they can choose what precautions, if any, they want to take. Adult mosquito control is not done on a set schedule. The decision to spray is determined by WNV levels in the adult mosquito population and expected weather conditions. It is often made the afternoon of the date of spraying. We are not able to contact the thousands of people in the district that will be in an area that will be treated on any given evening.

We do, however, provide several means for people to find out our spray plans. During business hours—7 a.m. to 3:30 p.m. Monday through Friday—residents can call and ask what our spray plans are for that evening. After hours, a recorded message will give the [location of] areas to be sprayed that evening if spraying is scheduled. In addition, our website will list the areas to be sprayed when planned. Many villages in the district have the ability to send out a phone message, or an email alert to residents. We contact villages that are to be sprayed so they can contact residents.

Patch: Do residents need to take any special precautions when fogging is occurring in their area?

Geery: If residents wish to avoid exposure to the pesticide, it is suggested that windows be closed, particularly those facing the street. Staying indoors will also prevent exposure.

Patch: Is there anything else that residents should know about fogging?

Geery: The main thing would be that the fogging is supplemental, and does not occur very often. The main mosquito control effort by the district is the control of mosquitoes in the larval stage.

Patch: Thanks Paul. We really appreciate your help in answering these questions from residents. Thanks for keeping the skeeters in control!

For more information about when spraying will occur, and how to sign up for alerts from your village, contact the , , or the by clicking the name above for contact information.