Mosquito Dunks (Effective, Safe and Affordable!)

By: Peter
Last updated:
mosquito larvae eat mosquito dunks

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Do you have standing water in your garden and a problem with mosquitoes?

If so, mosquito dunks could be the perfect solution. They are effective, safe, and inexpensive.

Read on to find out how and where to use them.

What are mosquito dunks?

a mosquito dunk
a mosquito dunk

Mosquito dunks are donut-like objects that can be thrown into stagnant water to kill mosquito larvae.

They dissolve over time and release bacteria that are harmful to mosquito larvae, fungus gnats, and black fly larvae.

The bacteria they release is Bacillus thuringiensis serotype israelensis (Bti).

Bacillus thuringiensis (Bt) is a naturally occurring bacteria found in soils. When eaten by larvae, Bt produces proteins that are toxic to immature insects. There are many different types of Bt that target other larvae. To eliminate mosquitoes, it’s the israelensis serotype.

Although mosquito dunks are discussed in this article, Bti is available in other forms – including tablets, briquettes, pellets, granules, or liquid.

Bti has been used as a larvicide in mosquito control for more than 30 years.

How do you use dunks?

They’re very easy to use! You just add them to any standing water in your garden by dropping them in. The dunk will float while slowly dissolving and releasing the bacteria.

If you have a small quantity of water to treat, you can break the dunk into smaller pieces to use just what’s needed.

Another alternative to dunks for small areas of water, like a birdbath, rain barrel, water gardens, or clogged roof gutters, is Bti bits. Bits can also be used where water causes swamp conditions.

How do they work?

Females mosquitoes lay their eggs in the water, the larvae hatch.

The floating dunk slowly releases the Bti on the surface of the water. The bacteria gradually sink into the water. While it is sinking, it is eaten by the larvae.

In the water, the dunks will only kill the larvae, commonly known as wrigglers. They do not affect adult mosquitoes. So you will have to use other ways to kill these adults or wait for them to die off. Once this is done, you should start to see a difference in the adult mosquito population originating from the water on your property.

Where do you use them?

Dunks can be used in any areas where water may collect that can’t be drained or prevented. This could be in ponds, rain barrels, unused swimming pools, roadside ditches, or animal feeding troughs.

Prevention is always better! Eliminate standing water by physical means if possible. Empty or turn over any containers, not in use. Change water in birdbaths, flowerpots, and pet drinking bowls at least once a week. Make sure your roof gutters aren’t blocked.

Mosquito dunks can also be used on the soil in areas with poor drainage. This could be before heavy rain is forecast, anywhere where puddles may form.

I have seen puddles formed by poor drainage from a septic tank. The puddles were full of larvae. Breaking the dunks into small pieces and spreading over the soil would allow the Bti to release into the water, where the larvae would feed on it and die.

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summit mosquito dunks
Summit Mosquito Dunks

Dunks or Bits

Mosquito dunks release the Bti slowly, over 30 days, as they float on the water. When the dunk has disappeared, it’s time to replace it. They are designed to be used in larger areas of water, such as ponds, but can be used in any standing water.

The dunks can be broken into pieces for smaller water surfaces, such as rain barrels or birdbaths. If you need only a small quantity of dunk pieces or don’t want to break the dunks yourself, another product, mosquito dunk chunks, might be more practical. Each chunk treats a surface of up to 25 sq feet.

Dunks are available in packs of 2, 6, or 20.

mosquito bits
Mosquito Bits

Mosquito bits are designed to release the Bti rapidly to kill any mosquito larvae in 24 hours. They need to be re-applied every 7 to 14 days to give good results. They can be sprinkled over standing water, used on waterlogged, swampy ground, or tire tracks with water.

Another use of bits is treating fungus gnats in your plants. Add some bits to water (4 tablespoons for 1 gallon of water) and leave for 30 minutes. Then skim off and floating bits, stir thoroughly, and water your plant with the solution. Repeat weekly for three weeks, and your fungus gnats should have disappeared.

Mosquito bits are available in 8oz, 30oz, or 20lb bags.

What season are they most effective?

When the temperatures start to rise, it’s time to use mosquito dunks.

As they aim to kill mosquito larvae, it’s good to use at the start of the breeding cycle. This could be as early as February in the northern hemisphere, but more commonly in March/ April.

The dunk should last about 30 days. Once the initial dunk has dissolved, you should add another dunk and so on until the end of the mosquito season.

Are mosquito dunks safe for humans and animals?

Yes, dunks are safe to use around children, birds, fish, insects, or pets.

Bti has been registered by the United States Environmental Protection Agency (EPA). EPA registered insecticides have been studied both for their effectiveness and safety.

The Bti contained in mosquito dunks targets only mosquito, black fly, and fungus gnat larvae. All other organisms in the water are unharmed. The EPA has registered Dti for use in animal water troughs and habitats where there are fish.

Dunks can be safely used in standing water without harming food crops or the water supply.

If a child accidentally drinks water containing mosquito dunks or even eats a piece of a dunk, they should be fine. A word of caution – if it is only Bti in the water, then it’s probably fine. However, you will have no way of knowing what else is lurking in the water in your garden.

As with all chemical products, it’s best to keep them out of reach of children.

Although dunks are considered safe, avoid getting particles on your skin or in your eyes, and it’s advised not to inhale the dust. They can cause irritation. So handle with care and wash your hands after using.

Are they safe for plants?

Yes, the dunks are safe for plants, both ornamental and vegetable. They can be broken up and placed in pots that retain water or put in watering cans used to water plants.

The dunks aren’t detrimental to plant health. They won’t affect the taste or aspect of your fruit and vegetables.

They will eliminate the wrigglers and any fungus gnat larvae in the soil.

Bti is approved for use in organic agriculture.

How long do they work?

A mosquito dunk will last 30 days and can treat an area of about 100 square feet of water. For smaller areas of water, you can break the dunk into smaller pieces.

If there is a risk of the dunk being washed out of an area of water, it can be secured by string, wire, a stake, or any other way you can think of.

If there are fish in the water, they may eat the dunk. This won’t harm the fish, but the dunk will be used much faster. Another dunk will have to be added to the water sooner than expected, making it more expensive to use. You can protect the dunk with some fine netting or mesh to avoid this.

Are they cheap to use?

Considering their effectiveness, mosquito dunks are pretty cheap to use. Compared to other products aimed at repelling, protecting you, or killing adult mosquitoes, the dunks attack your mosquito problem at its source.

The Bti kills the mosquito larvae before they grow up to become biting and disease-spreading adults.

A budget of around $12 for six dunks will probably be enough to treat any standing water on your property for a year or more. Of course, this will depend on your particular conditions.

They can be purchased on cards with 2, 6, or 20 dunks.

If you have too many dunks for this year, no problem! They can be stored in a cool, well-ventilated environment. Temperatures of more than 100°f can affect their efficacy. If they become wet and then dry out, this should not affect the dunks’ effectiveness.

Government mosquito control programs tested mosquito dunks that were eight years old and found they were almost as effective as new dunks.

If your neighbor has standing water that he doesn’t treat, you could also suggest that he uses mosquito dunks. Or even give him one or two dunks to try. After all, it’s to everyone’s advantage!

Conclusion – Are mosquito dunks effective?

Dunks containing Bacillus thuringiensis serotype israelensis are a safe, natural way to kill mosquito larvae. This can avoid having a new infestation of female mosquitos looking for a blood meal.

Mosquito dunks can be used in any standing water and don’t create a danger for children, pets, plants, or wildlife. Effective and easy to utilize, they can work alongside any other anti-mosquito products.

If you have a problem with mosquitoes originating from standing water on your property, try them out, I’m sure you’ll be impressed.

Mosquito Control

Using a larvicide is one component of mosquito control. It is less permanent than eliminating the breeding grounds. So you should continue to remove any larval habitats wherever possible.

A mosquito trap might be another consideration to reduce the adult population. The mosquitoes might be coming from somewhere in the neighborhood that you can’t access, so a trap could help.

Repellents are another weapon in your arsenal. This could be mosquito coils, a repellent you apply to any bare skin, or lanterns that emit a repellent.

The other choice is to wear a long sleeve shirt and trousers. Don’t forget to cover your feet; some mosquitoes seem to love this part of your anatomy.

Frequently Asked Questions

Do mosquito dunks really work?

Yes, they are very effective against mosquito larvae. However, they don’t kill adult mosquitoes. When dunks are added to standing water, a female mosquito can lay her eggs, which will hatch as normal. Then the resulting larvae will eat the Bti contained in the dunks and die.

Do mosquito dunks have an expiration date?

No, they don’t have an expiration date. Tests have shown that dunks 8 years old still work well. Store in a cool, well-ventilated place, and they should be fine for several years.

How do mosquito dunks work?

When a dunk is added to water, it will start to dissolve, releasing a bacteria, Bacillus thuringiensis serotype israelensis (Bti). The bacteria gradually sink into the water. While it is sinking, it is eaten by the mosquito larvae. Bti produces proteins that are toxic to mosquito larvae and larvae only. Adult mosquitoes remain unharmed by the use of dunks.

Are mosquito dunks safe for chicken?

Yes, mosquito dunks can be used safely with chicken. They can be used in their water feeders. Even if the chicken peck a dunk, they won’t be affected, and their eggs will be safe for consumption.

Will mosquito dunks kill my fish?

No, they won’t kill your fish. Even if your fish eat a mosquito dunk, they will be fine. The toxins produced by Bti only affect mosquito larvae, fungus gnats, and black fly larvae.

Are mosquito dunks safe for pets?

Yes, they are safe for all pets. If your cat or dog eats a dunk, they will just have an extra dose of protein.

When can I use mosquito dunks?

They can be used in all forms of standing water around your property. It’s best to start using them in early springtime at the start of the mosquito season.

What is the active ingredient of mosquito dunks?

Bacillus thuringiensis serotype israelensis (Bti) is the active ingredient of mosquito dunks. It’s a bacteria that kills mosquito larvae but is safe for other animals and humans.

Are mosquito dunks safe for bees?

Yes, dunks are safe for bees. Bti produces toxins that affect the larvae of mosquitoes, black flies, and fungus gnats. These toxins do not affect other insects or honey bees.

Are mosquito dunks safe for bees?

Yes, dunks are safe for bees. Bti produces toxins that affect the larvae of mosquitoes, black flies, and fungus gnats. These toxins do not affect other insects or honey bees.

Are mosquito dunks safe for birds?

Yes, they are safe for birds. Dunks can be safely used in birdbaths.

Where can I buy mosquito dunks?

You can buy them in many garden centers or hardware stores. Or order online from retailers such as Amazon or Home Depot.

What kinds of mosquito larvae will a mosquito dunk kill?

According to the manufacturer, the Bti in mosquito dunks will kill the larvae of all species of mosquitoes.

How much water will one dunk treat?

You can treat 100 square feet of water with one dunk. For smaller areas, you can break the dunks into pieces. If you have more than 100 sq ft, you will need more than one dunk.

Photo of author


Peter spends most of his time outside in his large garden. He has been fighting mosquitoes for a few years trying different traps and repellents without using agressive chemicals.