Sterile mosquitoes vs fogging

How fogging works

Two very different things go by the same name: the city's truck and the fogger in your garage.

Truck and aerial spraying (ULV)

When local officials decide it's needed, mosquito control programs spray from trucks or aircraft. The EPA describes these ultra-low volume (ULV) sprays as "very fine aerosol droplets that stay aloft and kill flying mosquitoes on contact," typically at less than 3 ounces per acre.¹ Communities use them to respond to an outbreak of mosquito-borne disease or a very heavy nuisance infestation.¹

The CDC says spraying is done when mosquitoes are most active and pollinating insects are not, and that crews may treat an area again.³ Because the droplets work while they're in the air, a single pass doesn't keep killing mosquitoes for days afterward.

In Dallas, Code Compliance traps mosquitoes weekly, applies larvicide to known breeding sites and storm drains, and keeps a courtesy "do not spray" list for residents who opt out of ground spraying.⁴ Ground spraying there has been triggered by a positive trap plus high counts over several weeks.⁵

Backyard thermal foggers

A thermal fogger uses heat, usually from a propane flame, to make a thick white fog that drifts through leaves and kills the mosquitoes resting there. Texas A&M AgriLife Extension says foggers can suppress mosquitoes for several hours or more, sometimes into the next day, and are meant to be used just before an outdoor event.² The visible smoke can alarm neighbors, and AgriLife warns that foggers may harm bees, butterflies and predatory insects.²

Neither kind of fog leaves a lasting layer. AgriLife rates fast-knockdown ingredients such as pyrethrins and phenothrin as lasting minutes to hours, and says malathion applied as an ultra-low volume spray has a short residual life.² The mosquitoes that hatch tomorrow, in gutters, drains and the yard next door, meet no insecticide.

How sterile males work

Biological control that's precisely targeted: it affects only the two mosquito species we release, so it's safe for people, pets, pollinators and the environment.

Fog works for a night. Sterile males seek out wild females every day, with no one flipping a switch, including in places fog never settles. Their eggs don't hatch, so the local population collapses, generation by generation.

Side by side

Here's how city programs, a backyard fogger and sterile males compare.

When fogging is the right choice

Fogging does a job sterile males don't, and it's fair to say so.

Public health response. When trap data shows disease activity, cities and districts need to cut the number of infected adult mosquitoes quickly across a wide area. Fogging reaches night-biting mosquitoes, which sterile Aedes males don't affect. That decision belongs to your local health officials, and it's the right tool for it.

A party on Saturday, before any releases. If guests arrive in a few hours and you haven't started a program, AgriLife's advice holds: a fogger used just before the event is the fast option.² Sterile males work on the next generation, so the effect keeps building.

Using them together

City programs and sterile males do different jobs. Your city responds to trap results, often at night. Sterile males work on the daytime and dusk biters in yards, all season.

Some practical notes:

• An adulticide kills any mosquito it touches, including released males. Our rule: any fogging on your property should happen at least one week before your first release, and not after releases start. If your city announces spraying nearby, let us know and we'll plan the next release with you.
• In Dallas, residents who'd rather not be ground sprayed can join the city's "do not spray" list through 311. It must be renewed each season and covers ground spraying only.⁴
• Removing standing water helps every program. For water you can't dump, see larvicides and dunks.

For cities and districts weighing a sterile-male pilot alongside existing programs, see our municipal programs.