Mosquito misters: solace or toxic rip-off?

At Toxic Free NC we get a lot of questions about how to handle pest problems without resorting to poisons. One of the products that seems to generate the most calls and emails lately is the backyard mosquito misting system, marketed under various trade names such as MosquitoNix, Mister Mosquito and others.

With a price tag in the thousands and soothing advertisements that offer freedom from mosquitoes using "natural botanicals," the mosquito mister is quickly becoming this season's Gucci handbag for homeowners. The question we keep getting is:

• Do they work?

...and a close second, from some of our long-time supporters:

• How do I convince my neighbors not to buy this poison-mister?

Both good questions. Let's start with the 'do they work' question. A recent bulletin from NCSU entomologists Charles Apperson and Mike Waldvogel states: "We have not seen any scientific studies regarding the true efficacy of these systems in controlling mosquitoes." Here are a few reasons why the misters won't work well in North Carolina:

• The systems don't prevent mosquitoes. They could kill mosquitoes who happen to be flying by when the mist is released. However, once the mist disperses, mosquitoes can fly back into the area safely.
• Actively killing adult mosquitoes is most conducive to human comfort during the time and in the area where humans are present. Clearly, "when humans are present" is not the appropriate time and place to be applying a fine insecticide mist.
• The system is timed to release a cloud of insecticide in the morning and again in the evening. Our most active mosquito species, the Asian Tiger mosquito, is active all day long, so the system would miss the vast majority of our nastiest mosquito pest's activity.
• Futhermore, spraying the same insecticide over and over, day-in and day-out, is a good way to experiment with inducing insecticide resistance in your local mosquito population. A system that might have provided temporary relief in the beginning would lose effectiveness over time.

Now, on to the implied "are they safe?" part of question #2. The "natural botanical" you keep hearing about in the MosquitoNix commerical is pyrethrin. While pyrethrin is derived from chrysanthemums, that doesn't make it benign. Pyrethrin is also just one of the ingredients in the insecticide formulation, which also includes chemical synergists, propellants, and other "inert" ingredients. Pyrethrin is a broad-spectrum insecticide that will also kill any other flying insects that happen to be in the path of the mosquito mist -- including butterflies, bees, dragonflies... get the idea? It's not a mosquito seek-and-destroy weapon.

A few weeks ago at a backyard cookout, I witnessed an asthmatic child have a frightening wheezing episode after he inhaled the mosquito repellent mist that an adult was applying to herself nearby. Inhaling a fine mist - even one that contains "natural botanicals" - can be dangerous, especially for children.

If you ask an entomologist how to prevent mosquitoes in your backyard, they will undoubtedly give you the tried-and-true methods: remove standing water, wear long pants and sleeves when you can, choose a safe insect repellent if you're outdoors when mosquitoes are active, and for areas with standing water that can't be drained, use mosquito dunks made from Bt (Bacillus thuringiensis israelensis) to prevent larvae from becoming adults. More on mosquito prevention.

In summary: mosquito misters seem to be a really expensive way to kill a handful of random flying insects twice a day. If you want to avoid mosquito bites, you don't have to spend a lot of money or use a lot of chemicals - just some common sense.