Everything you need to know about ‘Mosquito Dunks’: What is Bti? How does it work? Is it safe?

Mosquitoes complete their life cycle in about a week

Bti dunk used to kill mosquito larvae. (CDC)

Mosquitoes use standing water to breed, which is why you should make sure there isn’t any standing water on your property. But what if you can’t get rid of the standing water? That’s where Bti becomes useful.

If you can’t empty, scrub or cover items that hold water you can use Bti to kill off any mosquito larvae that could be hatching in there. So, what is Bti? Below is information from the EPA and CDC regarding Bti and its safety.

What is Bti?

Bti is a bacterium that occurs naturally in soil.

Bti is short for Bacillus thuringiensis subspecies israelensis. It has been used in mosquito control for more than 30 years.

According to the EPA, Bti contains spores that produce toxins that only affect the larvae of the mosquito, blackfly and fungus gnat.

Five different strains of Bti have been registered with the EPA and can be found in 48 pesticide products approved for residential, commercial and agricultural use.

How does Bti work?

Bti kills mosquito, black fly, and fungus gnat larvae.

After larvae eat the spores, it causes the larvae to stop eating and die. It only works against actively feeding larvae and does not affect mosquito pupae or adults.

By killing the larvae soon after they hatch from eggs, the Bti helps reduce mosquito populations overall.

Studies have shown that Bti is effective in reducing mosquito larval populations. It could be effective in controlling mosquitoes carrying Zika, dengue and chikungunya in places like Puerto Rico -- or other areas where the diseases have been identified.

Read: Let’s talk about Michigan mosquitoes: Are they eating you alive? Here’s what to know

Mosquito (Culex) larvae in standing water, Atlanta, Georgia, 2003. Image courtesy Centers for Disease Control (CDC) / James Gathany. Image courtesy CDC. (Photo by Smith Collection/Gado/Getty Images) (Photo by Smith Collection/Gado/Getty Images)

How do you use Bti?

Bti is available in several forms, including dunks, tablets, briquettes, pellets, granules, or liquid.

It can be added to standing water or containers that cannot be emptied out, covered, or turned over every week. Those containers could be rain barrels, fountains, ornamental ponds and pools that are not in use.

Bti can also be applied using trucks, airplanes, handheld sprayers or by tossing it by hand.

Read: Michigan’s first mosquito-borne virus of 2022 detected -- here’s what you need to know

Is Bti dangerous for humans or animals?

Bti is not toxic to people and has not been shown to make people sick, according to both the CDC and EPA.

It is not believed to harm people, pets, other animals, aquatic life or other insects.

Bti can be applied to a mosquito habitat without impacting food crops or water supplies. Bti can be used for pest control in organic farming.

The EPA said it is important to follow the label to make sure the Bti product is being used correctly. There are several products that can be used on certain drinking water while others are not intended for drinking water use.

According to the EPA, studies have indicated that “Bti has minimal toxicity to honey bees.” Bti produces toxins that specifically affect the larvae of only mosquitoes, black flies and fungus gnats. These toxins do not affect other types of insects, including honey bees.

Can insects become resistant to Bti?

No. There is no documented resistance to Bti.

A 2013 study confirmed previous research that showed a lack of Bti resistance in mosquito populations that had been treated for decades, according to the EPA.

Read: Mosquitoes are buzzing around Michigan: Here’s how to protect yourself from bites, diseases

What can I do to prevent mosquito bites?

Mosquitoes need standing water to reproduce. That’s why you should empty, scrub or cover any items that hold water.

Standing water is often found in old tires, buckets, planters, toys, pools, birdbaths, flower pot saucers or trash containers.

Mosquitoes can complete their life cycle in about a week. The CDC recommends using an outdoor insect spray made to kill adult mosquitoes. Mosquitoes are often found in dark, humid areas.

Michigan officials suggest taking the following steps:

  • Apply insect repellents that contain the active ingredient DEET, or other EPA-approved products to exposed skin or clothing. Always follow the manufacturer’s directions for use.
  • Wear light-colored, long-sleeved shirts and long pants when outdoors. Apply insect repellent to clothing to help prevent bites.
  • Maintain window and door screening to help keep mosquitoes outside.
  • Empty water from mosquito breeding sites around the home, such as buckets, unused kiddie pools, old tires or similar sites where mosquitoes lay eggs.

Read: Dress accordingly: Mosquitoes attracted to certain colors more than others, study finds

Sources: CDC, EPA

About the Author:

Kayla is a Web Producer for ClickOnDetroit. Before she joined the team in 2018 she worked at WILX in Lansing as a digital producer.